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RobH
Guest

Wed Jan 29, 2020 10:45 pm   



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

RheillyPhoull
Guest

Thu Jan 30, 2020 1:45 am   



On 30/01/2020 4:48 am, RobH wrote:
Quote:
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.

RobH
Guest

Thu Jan 30, 2020 1:45 pm   



On 30/01/2020 00:44, RheillyPhoull wrote:
Quote:
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

Andy Bennet
Guest

Thu Jan 30, 2020 1:45 pm   



On 29/01/2020 20:48, RobH wrote:
Quote:
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


I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?

Andy Bennet
Guest

Thu Jan 30, 2020 1:45 pm   



On 29/01/2020 20:48, RobH wrote:
Quote:
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


I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?

RobH
Guest

Thu Jan 30, 2020 3:45 pm   



On 30/01/2020 12:16, Andy Bennet wrote:
Quote:
On 29/01/2020 20:48, 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

I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?


Yes, the led does light up when the ldr is shaded. Now I have connected
the 5v buzzer across the led , and it beeps when the ldr is shaded .

The author shows it working fine, but he did not state what type of
buzzer he used. I just bought an Adafruit 3v to 5v buzzer, and expected
it to work, but it didn't in the way it was connected.
Had I realised or even checked that there was no output from pin 3 on
555 initially, I would have eventually found a way round it.

default
Guest

Thu Jan 30, 2020 4:45 pm   



On Thu, 30 Jan 2020 12:16:31 +0000, Andy Bennet <andyb_at_andy.com>
wrote:

Quote:
On 29/01/2020 20:48, 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

I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?


Ditto that. An op amp running from a single supply should be
referenced to a voltage divider setting the input at 1/2VCC or some
voltage less than VCC to work properly.

Another glaring mistake is the 100K pot wired to go to zero ohms. Zero
ohms or close-to with full light on the photocell may well burn out
the pot.

AND isn't the logic all backwards? Looks to me like the photocell
seeing light will drop the voltage at the inverting input which should
send the output of the op amp high, turning on the transistor/LED, and
sending the input to the 555 low, triggering it on. (output at pin 3
high, piezo buzzer sounding)

Typically you'd want to detect the absence of light as the beam is
broken. Or did I miss something here?

AND I'd use a photo transistor those CDS cells are often
moisture/humidity sensitive and degrade over time in wet environments
unless hermetically sealed.


Guest

Thu Jan 30, 2020 4:45 pm   



On Wednesday, 29 January 2020 20:48:16 UTC, RobH wrote:
Quote:
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

default
Guest

Thu Jan 30, 2020 4:45 pm   



On Thu, 30 Jan 2020 14:09:19 +0000, RobH <rob_at_despammer.com> wrote:

Quote:
On 30/01/2020 12:16, Andy Bennet wrote:
On 29/01/2020 20:48, 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

I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?


Yes, the led does light up when the ldr is shaded. Now I have connected
the 5v buzzer across the led , and it beeps when the ldr is shaded .

The author shows it working fine, but he did not state what type of
buzzer he used. I just bought an Adafruit 3v to 5v buzzer, and expected
it to work, but it didn't in the way it was connected.
Had I realised or even checked that there was no output from pin 3 on
555 initially, I would have eventually found a way round it.

There are several design errors in the schematic IMO. If he managed
to get it working, it is doing so in spite of the design, not because
of it.

In addition to my earlier comment, another WTF idea hit me, why in
hell does he find it necessary to use a op amp at all? A small signal
transistor has more than enough gain to operate directly from a CDS
cell, a mosfet would have more than enough to operate directly from a
photo transistor. I'll bet that explains how the reversed logic works
too. (the op amp isn't doing a damn thing necessary to the circuit)

Piezo buzzers use very little current and can operate directly from a
555 output without a driver transistor. If you are new to electronics
get a piezo buzzer that works at the voltage you have there, and don't
get a piezo transducer - they require driver circuitry to emit sound.

default
Guest

Thu Jan 30, 2020 4:45 pm   



On Thu, 30 Jan 2020 06:56:10 -0800 (PST), tabbypurr_at_gmail.com wrote:

Quote:
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


The 555 is desirable IMO. You'd want the thing to sound for a time to
raise an alarm. A person might run through the beam and break it for
a ~100 milliseconds or so.

That could be accomplished with a capacitor and RC network too, but a
555 is easily controlled and more predictable IMO.

amdx
Guest

Thu Jan 30, 2020 4:45 pm   



On 1/30/2020 9:28 AM, RobH wrote:
Quote:
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

RobH
Guest

Thu Jan 30, 2020 4:45 pm   



On 30/01/2020 14:56, tabbypurr_at_gmail.com wrote:
Quote:
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.

RobH
Guest

Thu Jan 30, 2020 4:45 pm   



On 30/01/2020 15:08, default wrote:
Quote:
On Thu, 30 Jan 2020 14:09:19 +0000, RobH <rob_at_despammer.com> wrote:

On 30/01/2020 12:16, Andy Bennet wrote:
On 29/01/2020 20:48, 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

I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?


Yes, the led does light up when the ldr is shaded. Now I have connected
the 5v buzzer across the led , and it beeps when the ldr is shaded .

The author shows it working fine, but he did not state what type of
buzzer he used. I just bought an Adafruit 3v to 5v buzzer, and expected
it to work, but it didn't in the way it was connected.
Had I realised or even checked that there was no output from pin 3 on
555 initially, I would have eventually found a way round it.

There are several design errors in the schematic IMO. If he managed
to get it working, it is doing so in spite of the design, not because
of it.

In addition to my earlier comment, another WTF idea hit me, why in
hell does he find it necessary to use a op amp at all? A small signal
transistor has more than enough gain to operate directly from a CDS
cell, a mosfet would have more than enough to operate directly from a
photo transistor. I'll bet that explains how the reversed logic works
too. (the op amp isn't doing a damn thing necessary to the circuit)

Piezo buzzers use very little current and can operate directly from a
555 output without a driver transistor. If you are new to electronics
get a piezo buzzer that works at the voltage you have there, and don't
get a piezo transducer - they require driver circuitry to emit sound.


Thanks, and yes I might as well be new to electronics as the last time I
did anything in this work was over 35 years ago, and have forgotten most
of what I knew then.

i should say that I am doing this as a hobby and not as anything serious
or professional.

default
Guest

Thu Jan 30, 2020 5:45 pm   



On Thu, 30 Jan 2020 15:22:49 +0000, RobH <rob_at_despammer.com> wrote:

Quote:
On 30/01/2020 15:08, default wrote:
On Thu, 30 Jan 2020 14:09:19 +0000, RobH <rob_at_despammer.com> wrote:

On 30/01/2020 12:16, Andy Bennet wrote:
On 29/01/2020 20:48, 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

I don't see how this ever worked. The op amp + input is effectively
connected to the + rail. The op amp output will never change state. Does
the LED change?


Yes, the led does light up when the ldr is shaded. Now I have connected
the 5v buzzer across the led , and it beeps when the ldr is shaded .

The author shows it working fine, but he did not state what type of
buzzer he used. I just bought an Adafruit 3v to 5v buzzer, and expected
it to work, but it didn't in the way it was connected.
Had I realised or even checked that there was no output from pin 3 on
555 initially, I would have eventually found a way round it.

There are several design errors in the schematic IMO. If he managed
to get it working, it is doing so in spite of the design, not because
of it.

In addition to my earlier comment, another WTF idea hit me, why in
hell does he find it necessary to use a op amp at all? A small signal
transistor has more than enough gain to operate directly from a CDS
cell, a mosfet would have more than enough to operate directly from a
photo transistor. I'll bet that explains how the reversed logic works
too. (the op amp isn't doing a damn thing necessary to the circuit)

Piezo buzzers use very little current and can operate directly from a
555 output without a driver transistor. If you are new to electronics
get a piezo buzzer that works at the voltage you have there, and don't
get a piezo transducer - they require driver circuitry to emit sound.


Thanks, and yes I might as well be new to electronics as the last time I
did anything in this work was over 35 years ago, and have forgotten most
of what I knew then.

i should say that I am doing this as a hobby and not as anything serious
or professional.


everything you need in one book

TimerOpAmpOptoelectronicCircuitsProjects

https://archive.org/download/TimerOpAmpOptoelectronicCircuitsProjects/Timer%2C%20Op%20Amp%20%26%20Optoelectronic%20Circuits%20%26%20Projects.pdf

or

https://tinyurl.com/rad7ate

I'd still go with the individual books - less daunting that way...

RobH
Guest

Thu Jan 30, 2020 5:45 pm   



On 30/01/2020 15:39, amdx wrote:
Quote:
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

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