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Jasen Betts
Guest

Fri Jan 31, 2020 7:43 am   



On 2020-01-30, RobH <rob_at_despammer.com> wrote:
Quote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm


and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png


I have the led, ldr and the 100k pot part of the circuit working fine,
but the buzzer from the 555ic does not work or sound as it is supposed
to do. (the buzzer is new and and has worked on another project)

I am using a BC327 pnp transistor as I don't have a BC557 transistor

The author clearly has it working fine, but I cannot get it fully
working.

Hopefully as per the schematic, I have a wire from pin 2 on 555ic to
the
emitter of the BC327, and also a wire from pin 3 of the 555ic to the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from the BC327
emitter, the buzzer does work, albeit when the ldr has not been
covered.This seems to be due to the capacitor across pins 1 and 2 of
the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do add a
diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and have
not touched electronics in over 35 years. I mistakenly thought that
the circuit and design I saw on that said website was how it should
be, but have now found that it is not.

 Hey guys, he said that pin 2 is moving up and down by changing light
input to the ldr. The problem as I see it, he said the voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to switch
the 555.
                   Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v and went
down to 2.57v after changing the light input to the ldr. On pin 3 it was
0v as before.


that circuit won't work on 5V it needs 9v there's too much voltage
drop in the transistor and the 741 output can't go low enough.

this mostly due to the choice of transistor. there should be a NPN part
there not PNP - then it will probably work on 5V
(eg BC337. BC547) emitter at the bottom this time.

then you might need to change stuff on the left around to get the alarm to
sound in the dark. (swap the LDR and the variable resistor positions)

then with a diode rightwards from the collector to pin4 you should ge
the alarm when it's dark. else you can have the diode leftwards and
get the alarm when the LED is unlit.

--
Jasen.

RobH
Guest

Fri Jan 31, 2020 11:45 am   



On 30/01/2020 19:16, amdx wrote:
Quote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from the
BC327
emitter, the buzzer does work, albeit when the ldr has not been
covered.This seems to be due to the capacitor across pins 1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said website
was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v and
went down to 2.57v after changing the light input to the ldr. On
pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and trigger
pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on pin 2
to ground caused the led to stay on and the buzzer to beep all the
time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets low
enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is not
being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a set
time and then go back low and wait for the next pin 2 trigger event.
Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse out
when pin 2 is triggered. I have not compared it to yours. I could, but
you should read the page to understand the 555, the 3rd diagram is a
schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


 A quick once over, and I think? that removing R3 and putting a short
there and then removing the connection from pin2 to the 10 uf cap will
make it put out a single pulse. But again I think?, the time of the
single pulse will be about 11 seconds with a 1Megohm and 10uf. with a
1uf it would be 1 second.
                              Mikek


Yes, removing R3 from pins 6 and 7 and then shorting the said pins
caused a continuos beep. Also I removed the 10uf capacitor from pin2 at
the same time.

RobH
Guest

Fri Jan 31, 2020 11:45 am   



On 30/01/2020 21:26, amdx wrote:
Quote:
On 1/30/2020 2:02 PM, RobH wrote:
On 30/01/2020 19:01, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from the
BC327
emitter, the buzzer does work, albeit when the ldr has not been
covered.This seems to be due to the capacitor across pins 1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said website
was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v and
went down to 2.57v after changing the light input to the ldr. On
pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and trigger
pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on pin 2
to ground caused the led to stay on and the buzzer to beep all the
time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets low
enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is not
being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a set
time and then go back low and wait for the next pin 2 trigger event.
Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

Yes that is correct, well maybe 2 seconds or for the length of time
the ldr is shaded or detecting.

 Sorry, you can't do, "for the length of time the ldr is shaded or
detecting" once pin 2 triggers, the 555 take control and does what it is
setup to do, pin 2 can't have control again until the 555 had its cycle.
 Sofor know we'll just do 2 seconds. Possibly address the other part
later.
 OK, we will work on the 555 timer first and get that to put out a 2
second pulse, when pin 2 is triggered?
 Remember for NOW, you are triggering pin 2 with you 100 ohm resistor
to ground, since that worked. I would put a 200k resistor in place of
R5. and put a short where R3 is and remove the connection from pin 2 to
the 10uf capacitor.

 You want your circuit to be wired like the 3rd image on this page,
https://www.electronics-tutorials.ws/waveforms/555_timer.html
labelled Monostable 555 timer.
 Once you get that, you should be able to insert, then remove your
100 ohm resistor (the pin 2 trigger) and hear a 2 second run of your
buzzer.

I watch a dozen or more videos looking for a good monostable 555 timer
tutorial, so far this is the best I can find, no completely happy but it
does describe a monostable 555 operation. I could not find one with a
native English speaker.
This is 12 minutes but worth your time to learn.

                        Mikek


Is there a link for the 12 minute video.
Thanks

amdx
Guest

Fri Jan 31, 2020 2:45 pm   



On 1/31/2020 4:24 AM, RobH wrote:
Quote:
On 30/01/2020 19:16, amdx wrote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from
the
BC327
emitter, the buzzer does work, albeit when the ldr has not
been
covered.This seems to be due to the capacitor across pins 1
and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said
website was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v
and
went down to 2.57v after changing the light input to the ldr.
On pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and
trigger pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on pin 2
to ground caused the led to stay on and the buzzer to beep all
the time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using a
100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets low
enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is not
being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a set
time and then go back low and wait for the next pin 2 trigger event.
Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse out
when pin 2 is triggered. I have not compared it to yours. I could,
but you should read the page to understand the 555, the 3rd diagram
is a schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


  A quick once over, and I think? that removing R3 and putting a short
there and then removing the connection from pin2 to the 10 uf cap will
make it put out a single pulse. But again I think?, the time of the
single pulse will be about 11 seconds with a 1Megohm and 10uf. with a
1uf it would be 1 second.
                               Mikek

Yes, removing R3 from pins 6 and 7 and then shorting the said pins
caused a continuous beep. Also I removed the 10uf capacitor from pin2 at
the same time.


Something is not correct in the wiring. It should only beep for the
amount of time it takes for the cap to charge to 2/3 Vc.
Mikek

default
Guest

Fri Jan 31, 2020 3:45 pm   



On Fri, 31 Jan 2020 07:44:20 +0800, RheillyPhoull
<Rheilly_at_bigslong.com> wrote:

Quote:
On 30/01/2020 7:50 pm, RobH wrote:
On 30/01/2020 00:44, RheillyPhoull wrote:
On 30/01/2020 4:48 am, RobH wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm


and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png


I have the led, ldr and the 100k pot part of the circuit working
fine, but the buzzer from the 555ic does not work or sound as it is
supposed to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557 transistor

The author clearly has it working fine, but I cannot get it fully
working.

Hopefully as per the schematic, I have a wire from pin 2 on 555ic to
the emitter of the BC327, and also a wire from pin 3 of the 555ic to
the positive side of the buzzer.

Now, the strange thing is after removing the said wire from the BC327
emitter, the buzzer does work, albeit when the ldr has not been
covered.This seems to be due to the capacitor across pins 1 and 2 of
the 555ic.

Thanks

What type of buzzer? ie. Is it one that just requires a DC voltage
supply or one that needs an an oscillating supply to drive it. If the
former then put it across the LED, perhaps with a "back" connected
diode just in case it produces som back emf. If the former then check
the output of the 555.

The output of the 555 pin 2 across the 10uf capacitor is 6.3v with no
ldr detection, and 4.6v with detection. The output from pin 3 is 0v.

The buzzer requires between 3v and 5v to work, so needs a DC voltage
supply.
Would a piezo electric buzzer do what I want it to do, beep when
detection is present.
Thanks
Just leave the 555 out and put the buzzer across the LED........"KISS"
principle


Leave the op-amp, and transistor out and trigger the 555 as a
monostable directly from the photo detector. The input impedance to
the internal comparator is high, the data sheet gives the current as
point five microamps. The sensor would have to connect to VCC and the
pot be in the ground leg to sense darkness.

amdx
Guest

Fri Jan 31, 2020 3:45 pm   



On 1/30/2020 1:16 PM, amdx wrote:
Quote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from the
BC327
emitter, the buzzer does work, albeit when the ldr has not been
covered.This seems to be due to the capacitor across pins 1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said website
was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v and
went down to 2.57v after changing the light input to the ldr. On
pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and trigger
pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on pin 2
to ground caused the led to stay on and the buzzer to beep all the
time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets low
enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is not
being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a set
time and then go back low and wait for the next pin 2 trigger event.
Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse out
when pin 2 is triggered. I have not compared it to yours. I could, but
you should read the page to understand the 555, the 3rd diagram is a
schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


 A quick once over, and I think? that removing R3 and putting a short
there and then removing the connection from pin2 to the 10 uf cap will
make it put out a single pulse. But again I think?, the time of the
single pulse will be about 11 seconds with a 1Megohm and 10uf. with a
1uf it would be 1 second.
                              Mikek

https://www.youtube.com/watch?v=TBRagQbsqpo


Mikek

amdx
Guest

Fri Jan 31, 2020 3:45 pm   



On 1/31/2020 7:52 AM, amdx wrote:
Quote:
On 1/30/2020 1:16 PM, amdx wrote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire from
the
BC327
emitter, the buzzer does work, albeit when the ldr has not
been
covered.This seems to be due to the capacitor across pins 1
and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2, but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said
website was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was 4.01v
and
went down to 2.57v after changing the light input to the ldr.
On pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and
trigger pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on pin 2
to ground caused the led to stay on and the buzzer to beep all
the time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using a
100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets low
enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is not
being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a set
time and then go back low and wait for the next pin 2 trigger event.
Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse out
when pin 2 is triggered. I have not compared it to yours. I could,
but you should read the page to understand the 555, the 3rd diagram
is a schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


  A quick once over, and I think? that removing R3 and putting a short
there and then removing the connection from pin2 to the 10 uf cap will
make it put out a single pulse. But again I think?, the time of the
single pulse will be about 11 seconds with a 1Megohm and 10uf. with a
1uf it would be 1 second.
                               Mikek

https://www.youtube.com/watch?v=TBRagQbsqpo

                   Mikek
http://www.hobby-circuits.com/circuits/timer/195/ne555-basic-monostable


Mikek

amdx
Guest

Fri Jan 31, 2020 5:45 pm   



On 1/31/2020 7:57 AM, amdx wrote:
Quote:
On 1/31/2020 7:52 AM, amdx wrote:
On 1/30/2020 1:16 PM, amdx wrote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire
from the
BC327
emitter, the buzzer does work, albeit when the ldr has not
been
covered.This seems to be due to the capacitor across pins
1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2,
but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said
website was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by
changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was
4.01v and
went down to 2.57v after changing the light input to the ldr.
On pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply, that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor from
pin 2
to ground, that should bring pin 2 down to about 1.3V and
trigger pin
3 to sound your buzzer. OR you could just ground pin 2 to make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on
pin 2
to ground caused the led to stay on and the buzzer to beep all
the time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using
a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets
low enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is
not being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep
when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a
set time and then go back low and wait for the next pin 2 trigger
event. Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second after
it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse out
when pin 2 is triggered. I have not compared it to yours. I could,
but you should read the page to understand the 555, the 3rd diagram
is a schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they
connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


  A quick once over, and I think? that removing R3 and putting a
short there and then removing the connection from pin2 to the 10 uf
cap will make it put out a single pulse. But again I think?, the time
of the single pulse will be about 11 seconds with a 1Megohm and 10uf.
with a 1uf it would be 1 second.
                               Mikek

https://www.youtube.com/watch?v=TBRagQbsqpo

                    Mikek
http://www.hobby-circuits.com/circuits/timer/195/ne555-basic-monostable

                             Mikek


Hi ROBH, I see others commenting on the first part of the circuit
while I has concentrated on the 555 part. I don't care which part you
work on first, but decide and then go from there. Don't work on both at
the same time. Truly, if you get an understanding of how the 555 works
it should
be easy.
Mikek

RobH
Guest

Fri Jan 31, 2020 6:45 pm   



On 31/01/2020 16:43, amdx wrote:
Quote:
On 1/31/2020 7:57 AM, amdx wrote:
On 1/31/2020 7:52 AM, amdx wrote:
On 1/30/2020 1:16 PM, amdx wrote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as
it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire
from the
BC327
emitter, the buzzer does work, albeit when the ldr has
not been
covered.This seems to be due to the capacitor across pins
1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2,
but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a hobby
and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said
website was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by
changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below 3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was
4.01v and
went down to 2.57v after changing the light input to the ldr.
On pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply,
that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor
from pin 2
to ground, that should bring pin 2 down to about 1.3V and
trigger pin
3 to sound your buzzer. OR you could just ground pin 2 to make
the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on
pin 2
to ground caused the led to stay on and the buzzer to beep all
the time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when using
a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets
low enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is
not being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to beep
when
the ldr sensed detection?, or was shaded by anything or anyone, I
guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a
set time and then go back low and wait for the next pin 2 trigger
event. Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second
after it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse
out when pin 2 is triggered. I have not compared it to yours. I
could, but you should read the page to understand the 555, the 3rd
diagram is a schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they
connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


  A quick once over, and I think? that removing R3 and putting a
short there and then removing the connection from pin2 to the 10 uf
cap will make it put out a single pulse. But again I think?, the
time of the single pulse will be about 11 seconds with a 1Megohm and
10uf. with a 1uf it would be 1 second.
                               Mikek

https://www.youtube.com/watch?v=TBRagQbsqpo

                    Mikek
http://www.hobby-circuits.com/circuits/timer/195/ne555-basic-monostable

                              Mikek

 Hi ROBH, I see others commenting on the first part of the circuit
while I has concentrated on the 555 part. I don't care which part you
work on first, but decide and then go from there. Don't work on both at
the same time. Truly, if you get an understanding of how the 555 works
it should
be easy.
                          Mikek


I've watched a few videos on 555 Monostable on youtube, and have made up
a couple of simple circuits to see how they work. I've also looked at a
couple of 555 Astable videos.

The circuit I did from the said website works for me just now and I'll
live with it until I know I can improve it. The link you gave me for the
hobby-circuits site should help with that.

Thanks for your help.

amdx
Guest

Fri Jan 31, 2020 6:45 pm   



On 1/31/2020 11:05 AM, RobH wrote:
Quote:
On 31/01/2020 16:43, amdx wrote:
On 1/31/2020 7:57 AM, amdx wrote:
On 1/31/2020 7:52 AM, amdx wrote:
On 1/30/2020 1:16 PM, amdx wrote:
On 1/30/2020 1:09 PM, amdx wrote:
On 1/30/2020 1:01 PM, amdx62_at_gmail.com wrote:
On Thursday, January 30, 2020 at 12:42:55 PM UTC-6, RobH wrote:
On 30/01/2020 17:56, amdx wrote:
On 1/30/2020 11:48 AM, RobH wrote:
On 30/01/2020 16:58, amdx wrote:
On 1/30/2020 10:30 AM, RobH wrote:
On 30/01/2020 15:39, amdx wrote:
On 1/30/2020 9:28 AM, RobH wrote:
On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
On Wednesday, 29 January 2020 20:48:16 UTC, RobH  wrote:
I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm



and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png



I have the led, ldr and the 100k pot part of the circuit
working
fine,
but the buzzer from the 555ic does not work or sound as
it is
supposed
to do. (the buzzer is new and and has worked on another
project)

I am using a BC327 pnp transistor as I don't have a BC557
transistor

The author clearly has it working fine, but I cannot get it
fully working.

Hopefully as per the schematic, I have a wire from pin 2 on
555ic to the
emitter of the BC327, and also a wire from pin 3 of the
555ic to
the
positive side of the buzzer.

Now, the strange thing is after removing the said wire
from the
BC327
emitter, the buzzer does work, albeit when the ldr has
not been
covered.This seems to be due to the capacitor across
pins 1 and
2 of the
555ic.

Thanks

LED output is dc. Your 5v buzzer can go across LED & R2,
but do
add a diode across it. The 555 is not needed.


NT


Ok thanks.
I have some diodes which I could use.

Pardon my ignorance, but as I am only doing this as a
hobby and
have not touched electronics in over 35 years. I mistakenly
thought that the circuit and design I saw on that said
website was
how it should be, but have now found that it is not.

   Hey guys, he said that pin 2 is moving up and down by
changing
light input to the ldr. The problem as I see it, he said the
voltage went down
to 4.6V on pin 2, that's not low enough, it must go below
3V to
switch the 555.
                     Mikek

Using a 5v supply the voltage across pin 2 on the 555 was
4.01v and
went down to 2.57v after changing the light input to the
ldr. On pin
3 it was 0v as before.

Thanks


    Pin 2 needs to go below 1/3 VCC, so with a 9 volt supply,
that
would be 3V, with a 5V supply that would be 1.6V.
If you put the 9v supply back in and put a 47 ohm resistor
from pin 2
to ground, that should bring pin 2 down to about 1.3V and
trigger pin
3 to sound your buzzer. OR you could just ground pin 2 to
make the
buzzer buzz. All of this is not the fix for your circuit, but
this is
to help you understand how the 555 behaves. If this works
then we
will figure out how to make the transistor pull it lower.
    Let me know.
                        Mikek

Using the 9v supply and either shorting or using a resistor on
pin 2
to ground caused the led to stay on and the buzzer to beep all
the time.
The voltage on pin 2 was 6.58v when shorted and 1.9v when
using a 100
ohm resistor. (Smallest I had)

   OK, so now you know that the 555 will trigger when pin gets
low enough.
How long did you want the buzzer to buzz? Was it any time the ldr
signaled it to or just one beep when the LDR made the change.
I don't know the purpose of the circuit.
We either have one problem to fix or two problems to fix. But I
need to
know what the buzzed is supposed to do.
   JUst to give you a head start, I suspect your transistor is
not being
turned off hard enough, meaning you can't bring pin 2 low enough.
   Might increase the 210 ohm to 500 ohms or 1000 ohms to start.
But that's getting ahead.
                                                Mikek


The idea of the buzzer , from the circuit I followed, was to
beep when
the ldr sensed detection?, or was shaded by anything or anyone,
I guess.
So yes , it was for when the ldr signaled it to.

The 555 can be setup two ways, for pin 3 to either go high for a
set time and then go back low and wait for the next pin 2 trigger
event. Or it will go high and stay high until it is manually reset.
  So it sounds like you only want it to beep for say 1 second
after it gets triggered. Is that correct?
                           Mikek

  Sorry, I could not see your last post (my problem), had to go to
google groups to read and post.
This website has the correct 555 schematic to get a single pulse
out when pin 2 is triggered. I have not compared it to yours. I
could, but you should read the page to understand the 555, the 3rd
diagram is a schematic of a one shot circuit.

https://www.electronics-tutorials.ws/waveforms/555_timer.html

It's just going to be a change of the resistors, and how they
connect to
the 555.
  Let me know where you are at on this.
                                               Mikek


  A quick once over, and I think? that removing R3 and putting a
short there and then removing the connection from pin2 to the 10 uf
cap will make it put out a single pulse. But again I think?, the
time of the single pulse will be about 11 seconds with a 1Megohm
and 10uf. with a 1uf it would be 1 second.
                               Mikek

https://www.youtube.com/watch?v=TBRagQbsqpo

                    Mikek
http://www.hobby-circuits.com/circuits/timer/195/ne555-basic-monostable

                              Mikek

  Hi ROBH, I see others commenting on the first part of the circuit
while I has concentrated on the 555 part. I don't care which part you
work on first, but decide and then go from there. Don't work on both
at the same time. Truly, if you get an understanding of how the 555
works it should
be easy.
                           Mikek

I've watched a few videos on 555 Monostable on youtube, and have made up
a couple of simple circuits to see how they work. I've also looked at a
couple of 555 Astable videos.

The circuit I did from the said website works for me just now and I'll
live with it until I know I can improve it. The link you gave me for the
hobby-circuits site should help with that.

Thanks for your help.


If I understand, you can now pull pin 2 low and the output make your
buzzer buzz for a second of two. Is that what happens?
Note: I'm not sure if pin 2 is required to have a momentary pull down
to zero or if you can just hold it at zero and the circuit will still do
it's timing event. Must situations just give pin 2 a short pull down.
It might be you just need to connect the 100 ohm resistor for just a
very short period and then remove it.
Mikek

Jasen Betts
Guest

Fri Jan 31, 2020 11:45 pm   



On 2020-01-30, default <default_at_defaulter.net> wrote:
Quote:
On Thu, 30 Jan 2020 11:56:55 -0600, amdx <nojunk_at_knology.net> wrote:


Look at the schematic
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png

That is the classic 555 astable multivibrator circuit, with the
addition of another external trigger. That is NOT what should be
there. He would want it as a retriggerable monostable multivibrator.
Stays on while light is blocked then times out when light is resumed.

That circuit will not work properly. The better idea is to use the
transistor to short the timing cap (threshold pin) to ground and
ignore the pin 2 trigger input entirely.


so, connect trigger to where?

Quote:
The author of the article, Pankaj Khatri, has no clue as to what he's
doing. If he did manage to get it to work (as planned) it isn't
because it was designed to work as planned.


--
Jasen.


Guest

Sat Feb 01, 2020 5:45 am   



On Friday, 31 January 2020 05:32:38 UTC, Jasen Betts wrote:
Quote:
On 2020-01-29, RobH <rob_at_despammer.com> wrote:

I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm

and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png


I have the led, ldr and the 100k pot part of the circuit working fine,

That's a surprise... there should be a resistor below R1.


I have a very vague memory of an opamp being treated like that and yet working. Looking at opamp input circuits reveals there are voltage swing limits and so-called phase inversion that complicate the picture. At this late hour I can't work out if it could actually work, but can't dismiss it out of hand.


NT

Andy Bennet
Guest

Sat Feb 01, 2020 9:45 am   



On 01/02/2020 04:03, tabbypurr_at_gmail.com wrote:
Quote:
On Friday, 31 January 2020 05:32:38 UTC, Jasen Betts wrote:
On 2020-01-29, RobH <rob_at_despammer.com> wrote:

I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm

and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png


I have the led, ldr and the 100k pot part of the circuit working fine,

That's a surprise... there should be a resistor below R1.

I have a very vague memory of an opamp being treated like that and yet working. Looking at opamp input circuits reveals there are voltage swing limits and so-called phase inversion that complicate the picture. At this late hour I can't work out if it could actually work, but can't dismiss it out of hand.


NT


General opamp theory says it does not work and never could.

If it does work then that is due to parameters way off the datasheet,
therefore not guaranteed to work for any or all devices.

The circuit "designer" does not have a clue, and seems to be playing
with all combinations of all pins of random devices until something
appears to work - and then publishing it.


Guest

Sat Feb 01, 2020 11:45 am   



On Saturday, 1 February 2020 08:33:53 UTC, Andy Bennet wrote:
Quote:
On 01/02/2020 04:03, tabbypurr wrote:
On Friday, 31 January 2020 05:32:38 UTC, Jasen Betts wrote:
On 2020-01-29, RobH <rob_at_despammer.com> wrote:

I have put together a circuit from here:
https://circuitdigest.com/electronic-circuits/light-fence-circuit-diagram-with-alarm

and this is the schematic:
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png


I have the led, ldr and the 100k pot part of the circuit working fine,

That's a surprise... there should be a resistor below R1.

I have a very vague memory of an opamp being treated like that and yet working. Looking at opamp input circuits reveals there are voltage swing limits and so-called phase inversion that complicate the picture. At this late hour I can't work out if it could actually work, but can't dismiss it out of hand.

General opamp theory says it does not work and never could.


General opamp theory doesn't come into it. General opamp theory only applies when 2 Rs are used on the input to set a known voltage.


Quote:
If it does work then that is due to parameters way off the datasheet,
therefore not guaranteed to work for any or all devices.


if it works, and the op at least says it does, it'll be due to the input circuit issues of the opamp, which should be sufficiently consistent for any one type of opamp.

Quote:
The circuit "designer" does not have a clue, and seems to be playing
with all combinations of all pins of random devices until something
appears to work - and then publishing it.


I really ought to lash one together & test it, but am way too occupied with other stuff atm.


NT

default
Guest

Sat Feb 01, 2020 3:45 pm   



On Fri, 31 Jan 2020 22:21:56 -0000 (UTC), Jasen Betts
<jasen_at_xnet.co.nz> wrote:

Quote:
On 2020-01-30, default <default_at_defaulter.net> wrote:
On Thu, 30 Jan 2020 11:56:55 -0600, amdx <nojunk_at_knology.net> wrote:


Look at the schematic
https://circuitdigest.com/fullimage?i=circuitdiagram/Automatic-Light-Fence-Circuit-Diagram-with-Alarm.png

That is the classic 555 astable multivibrator circuit, with the
addition of another external trigger. That is NOT what should be
there. He would want it as a retriggerable monostable multivibrator.
Stays on while light is blocked then times out when light is resumed.

That circuit will not work properly. The better idea is to use the
transistor to short the timing cap (threshold pin) to ground and
ignore the pin 2 trigger input entirely.

so, connect trigger to where?
ignore the trigger pin, no connection.


If you did wire a monostable (not the astable as shown) and use the
trigger, and hold it low longer than the time constant, it will glitch
periodically as it times out then resume timing. (assuming it is DC
coupled as this schematic shows)

Shorting the timing cap to ground insures the output changes state and
stays that way (no glitch) until the short is removed then times
normally until it times out.

The glitch is very fast, but can be noticeable in the load.
Quote:

The author of the article, Pankaj Khatri, has no clue as to what he's
doing. If he did manage to get it to work (as planned) it isn't
because it was designed to work as planned.


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