IR phototransistor reciever...

[sonnic...@gmail.com]

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there is only 0.07V on the resistor side (the 10K). In my room, with very little light I get only a 0.02 difference whether my IR LED is on or off.
On google I find example of a photo transistor feeding a normal LED directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a sensor/optokobler (I cut it in half and used them with a bigger distance)
Try my TV remote etc I get the same result, only a very week change.

The receiver is supposed to work on 3V or to batteries when ready.

Regardless of what I do I only get a weak change of 20-30mV. I can move LED and phototransistor and clearly see a difference in angles by a few mV.

Given that I work in a dark space, I could simple use a comparator or opamp to boost the signal, simply look at say signal > 0.04mV.

How are other peoples experiences with IR receiving?
I work at a low voltage, so recivers for Ardoino is not really an option. I and want the joy of working with this development

PS: I recall a friend many years ago using a 555 to send 2 frequencies for 0/1 and receiving it in the other end. Has anyone done anything similar?

 

[Phil Hobbs]

sonnic...@gmail.com wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the
signal. I just want to know whether my beam is broken. The system
will at the end work in a dark space. If blocked it will block almost
completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and
receiver.

Phototransistors are the wrong answer for almost anything in free space.

What are you using for a transmitter?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sat, 8 Jan 2022 11:51:11 -0800 (PST), \"sonnic...@gmail.com\"
<sonnichjensen@gmail.com> wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground.

Schematic?



--

I yam what I yam - Popeye

 

[whit3rd]

On Saturday, January 8, 2022 at 11:51:15 AM UTC-8, sonnic...@gmail.com wrote:

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

There has to be a range, and some idea of pointing, to be sure, but... the easy way is to use remote-control
receivers and modulated (alternately on/off) transmitters. Those are immune to things like sunlight
and sources that aren\'t modulated.

> I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

If you put a black hood over the receiver, and/or use a lens to collimate a point-source into a narrow beam,
and AIM the transmitter at the receiver, that can work at such distance. The signal from a photodiode will be
weaker than a logic ON/OFF unless you can perform that aim function (try viewing a white paper with
your cellphone as you aim the IR at it; cellphone cameras, some of \'em, can see the IR light).

Phototransistors have small collection area, that can hurt the signal; a lens focused at the transistor
might help, but will be tricky to adjust with infrared light. Since both ends will require (battery?) power,
a one-sided send/receive box and a retroreflective tape patch might be convenient. So would
an IR (or even just deep red) filter.

A phototransistor can read its illumination by grounding the emitter, leaving the base OPEN (unconnected)
and reading current into the collector from a +v source (battery) with a resistor and milliammeter;
the battery, resistor, phototransistor, and current meter are all in one series circuit.

 

[Spehro Pefhany]

On Sat, 8 Jan 2022 16:32:29 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

On Saturday, January 8, 2022 at 11:51:15 AM UTC-8, sonnic...@gmail.com wrote:

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

There has to be a range, and some idea of pointing, to be sure, but... the easy way is to use remote-control
receivers and modulated (alternately on/off) transmitters. Those are immune to things like sunlight
and sources that aren\'t modulated.

They are designed to receive *bursts* though and won\'t maintain the
output in the same state (low) if the modulated light signal persists.
So you\'d need to modulate the 38kHz (which needs to be fairly
accurate- maybe a few percent, so an untrimmed 555 is probably not
good enough) and then stretch the pulse with a retriggerable
multivibrator at the other end if you need to transmit levels that
persist for very long.

I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

If you put a black hood over the receiver, and/or use a lens to collimate a point-source into a narrow beam,
and AIM the transmitter at the receiver, that can work at such distance. The signal from a photodiode will be
weaker than a logic ON/OFF unless you can perform that aim function (try viewing a white paper with
your cellphone as you aim the IR at it; cellphone cameras, some of \'em, can see the IR light).

Phototransistors have small collection area, that can hurt the signal; a lens focused at the transistor
might help, but will be tricky to adjust with infrared light. Since both ends will require (battery?) power,
a one-sided send/receive box and a retroreflective tape patch might be convenient. So would
an IR (or even just deep red) filter.

A phototransistor can read its illumination by grounding the emitter, leaving the base OPEN (unconnected)
and reading current into the collector from a +v source (battery) with a resistor and milliammeter;
the battery, resistor, phototransistor, and current meter are all in one series circuit.

--
Best regards,
Spehro Pefhany

 

[Martin Brown]

On 08/01/2022 19:51, sonnic...@gmail.com wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

What optics do you have at either end?

Small lenses will make a big difference as will using visible light to
get started so you can see how big the beam sweet spot actually is. A
couple of 1cm lenses (clear marbles at a pinch would improve things).

Collimated beams should go a long way. We have done adjacent hill tops
optical links with a similar setup and modest 8\" SCT\'s. There was at one
time a plan to use a similar optical comms system in some US cities.

It is still a contender for long range high bandwidth satellite comms.

https://kiss.caltech.edu/workshops/optcomm/presentations/Sburlan.pdf


--
Regards,
Martin Brown

 

[Jasen Betts]

On 2022-01-08, sonnic...@gmail.com <sonnichjensen@gmail.com> wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and
receiver.

My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there is only 0.07V on the resistor side (the 10K). In my room, with very little light I get only a 0.02 difference whether my IR LED is on or off.
On google I find example of a photo transistor feeding a normal LED directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a sensor/optokobler (I cut it in half and used them with a bigger distance)

Remote control receivers don\'t use a (bare) phototransistor, but instead
special tuned infrared receiver IC, the IC looks for a signal modulated
at about 38kHz and returns a solid logic level signal when it sees one.

TSSP4038 is the same sort of thing but optimised for light barrier
applications - available for a couple of bucks if you don\'t look too hard.

As the frequiency filter is on-chip it\'s not very tight so a
good RC oscillator (like a 555) should be able to get close
enough to the sensing frequency for reliable operation if
you use a reasonably good timing capacitor. (main consideration:
use a temperature stable capacitor)

> The receiver is supposed to work on 3V or to batteries when ready.

TSSP4038 will operate from 2.5V to 5.5V so is suitable for 3.7V lithium or
4.5V carbon-zinc, carbon-zinc batteries drop to 1V per cell at nominal full
discharge so you\'ll need three to keep this receiver happy. unless you
want tho throw them out half-used.

Given that I work in a dark space, I could simple use a comparator
or opamp to boost the signal, simply look at say signal > 0.04mV.

You could build a frequency-pass circuit like the receiver ICs have
inside if you really want to. it should be possible to get even better
performance as its perfomance will not be contsrained by low precicion
on-chip resistors and capacitors.

--
Jasen.

 

[piglet]

On 08/01/2022 7:51 pm, sonnic...@gmail.com wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.

My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there is only 0.07V on the resistor side (the 10K). In my room, with very little light I get only a 0.02 difference whether my IR LED is on or off.
On google I find example of a photo transistor feeding a normal LED directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a sensor/optokobler (I cut it in half and used them with a bigger distance)
Try my TV remote etc I get the same result, only a very week change.

The receiver is supposed to work on 3V or to batteries when ready.

Regardless of what I do I only get a weak change of 20-30mV. I can move LED and phototransistor and clearly see a difference in angles by a few mV.

Given that I work in a dark space, I could simple use a comparator or opamp to boost the signal, simply look at say signal > 0.04mV.

How are other peoples experiences with IR receiving?
I work at a low voltage, so recivers for Ardoino is not really an option. I and want the joy of working with this development

PS: I recall a friend many years ago using a 555 to send 2 frequencies for 0/1 and receiving it in the other end. Has anyone done anything similar?

Are you doing this at DC with a the IRED continously on? You will need a
lot a gain at the receiver end and drift free DC gain is hard. This is
why almost all schemes use pulsed sources and AC amplification at the
detector. As a bonus the setup then ignores slowly varying ambient light
sources.

piglet

 

[server]

On Sun, 9 Jan 2022 09:29:39 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

On 2022-01-08, sonnic...@gmail.com <sonnichjensen@gmail.com> wrote:

Hi all

I have played around with IR beams, and I wonder how to receive the signal.
I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and
receiver.

My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there is only 0.07V on the resistor side (the 10K). In my room, with very little light I get only a 0.02 difference whether my IR LED is on or off.
On google I find example of a photo transistor feeding a normal LED directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a sensor/optokobler (I cut it in half and used them with a bigger distance)

Remote control receivers don\'t use a (bare) phototransistor, but instead
special tuned infrared receiver IC, the IC looks for a signal modulated
at about 38kHz and returns a solid logic level signal when it sees one.

TSSP4038 is the same sort of thing but optimised for light barrier
applications - available for a couple of bucks if you don\'t look too hard.

As the frequiency filter is on-chip it\'s not very tight so a
good RC oscillator (like a 555) should be able to get close
enough to the sensing frequency for reliable operation if
you use a reasonably good timing capacitor. (main consideration:
use a temperature stable capacitor)

The receiver is supposed to work on 3V or to batteries when ready.

TSSP4038 will operate from 2.5V to 5.5V so is suitable for 3.7V lithium or
4.5V carbon-zinc, carbon-zinc batteries drop to 1V per cell at nominal full
discharge so you\'ll need three to keep this receiver happy. unless you
want tho throw them out half-used.

Given that I work in a dark space, I could simple use a comparator
or opamp to boost the signal, simply look at say signal > 0.04mV.

You could build a frequency-pass circuit like the receiver ICs have
inside if you really want to. it should be possible to get even better
performance as its perfomance will not be contsrained by low precicion
on-chip resistors and capacitors.

Any AC processing, even untuned, will be a huge advantage over DC. As
will a modest optical bandpass filter on the receiver.

But maybe the op is making basic circuit mistakes. We don\'t know.



--

I yam what I yam - Popeye

 

[bitrex]

On 1/9/22 7:33 AM, piglet wrote:

On 08/01/2022 7:51 pm, sonnic...@gmail.com wrote:
Hi all

I have played around with IR beams, and I wonder how to receive the
signal.
I just want to know whether my beam is broken. The system will at the
end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and receiver.

My question is on the receiver. I have tried to feed base or gate of a
transistor, with my phototransistor on the plus side, 10K to the
base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there
is only 0.07V on the resistor side (the 10K). In my room, with very
little light I get only a 0.02 difference whether my IR LED is on or off.
On google I find example of a photo transistor feeding a normal LED
directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a
sensor/optokobler (I cut it in half and used them with a bigger distance)
Try my TV remote etc I get the same result, only a very week change.

The receiver is supposed to work on 3V or to batteries when ready.

Regardless of what I do I only get a weak change of 20-30mV. I can
move LED and phototransistor and clearly see a difference in angles by
a few mV.

Given that I work in a dark space, I could simple use a comparator or
opamp to boost the signal, simply look at say signal > 0.04mV.

How are other peoples experiences with IR receiving?
I work at a low voltage, so recivers for Ardoino is not really an
option. I and want the joy of working with this development

PS: I recall a friend many years ago using a 555 to send 2 frequencies
for 0/1 and receiving it in the other end. Has anyone done anything
similar?


Are you doing this at DC with a the IRED continously on? You will need a
lot a gain at the receiver end and drift free DC gain is hard. This is
why almost all schemes use pulsed sources and AC amplification at the
detector. As a bonus the setup then ignores slowly varying ambient light
sources.

piglet

Not sure it\'s directly applicable to OP\'s problem but there was this
kinda cool circuit for increasing phototransistor tolerance to ambient
light:

<https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/>

 

[piglet]

On 09/01/2022 7:32 pm, bitrex wrote:

On 1/9/22 7:33 AM, piglet wrote:
On 08/01/2022 7:51 pm, sonnic...@gmail.com wrote:
Hi all

I have played around with IR beams, and I wonder how to receive the
signal.
I just want to know whether my beam is broken. The system will at the
end work in a dark space. If blocked it will block almost completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and
receiver.

My question is on the receiver. I have tried to feed base or gate of
a transistor, with my phototransistor on the plus side, 10K to the
base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there
is only 0.07V on the resistor side (the 10K). In my room, with very
little light I get only a 0.02 difference whether my IR LED is on or
off.
On google I find example of a photo transistor feeding a normal LED
directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a
sensor/optokobler (I cut it in half and used them with a bigger
distance)
Try my TV remote etc I get the same result, only a very week change.

The receiver is supposed to work on 3V or to batteries when ready.

Regardless of what I do I only get a weak change of 20-30mV. I can
move LED and phototransistor and clearly see a difference in angles
by a few mV.

Given that I work in a dark space, I could simple use a comparator or
opamp to boost the signal, simply look at say signal > 0.04mV.

How are other peoples experiences with IR receiving?
I work at a low voltage, so recivers for Ardoino is not really an
option. I and want the joy of working with this development

PS: I recall a friend many years ago using a 555 to send 2
frequencies for 0/1 and receiving it in the other end. Has anyone
done anything similar?


Are you doing this at DC with a the IRED continously on? You will need
a lot a gain at the receiver end and drift free DC gain is hard. This
is why almost all schemes use pulsed sources and AC amplification at
the detector. As a bonus the setup then ignores slowly varying ambient
light sources.

piglet


Not sure it\'s directly applicable to OP\'s problem but there was this
kinda cool circuit for increasing phototransistor tolerance to ambient
light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/

Interesting find! One old-school solution to that problem was to operate
the phototransistor into an inductor.

piglet

 

[Jeroen Belleman]

On 2022-01-09 20:40, piglet wrote:
[...]

Not sure it\'s directly applicable to OP\'s problem but there was
this kinda cool circuit for increasing phototransistor tolerance to
ambient light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/


Interesting find! One old-school solution to that problem was to
operate the phototransistor into an inductor.

piglet

They want me to switch off my adblocker. Sorry, but no.

Jeroen Belleman

 

[server]

On Sun, 09 Jan 2022 22:32:46 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 2022-01-09 20:40, piglet wrote:
[...]

Not sure it\'s directly applicable to OP\'s problem but there was
this kinda cool circuit for increasing phototransistor tolerance to
ambient light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/


Interesting find! One old-school solution to that problem was to
operate the phototransistor into an inductor.

piglet


They want me to switch off my adblocker. Sorry, but no.

Jeroen Belleman

No loss. It\'s truly lame.

I wonder why some people design elaborate lowpass filtered negative
feedback loops to accomplish AC coupling. There are easier ways.



--

I yam what I yam - Popeye

 

[Spehro Pefhany]

On Sat, 08 Jan 2022 20:05:46 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

They are designed to receive *bursts* though and won\'t maintain the
output in the same state (low) if the modulated light signal persists.
So you\'d need to modulate the 38kHz (which needs to be fairly
accurate- maybe a few percent, so an untrimmed 555 is probably not
good enough) and then stretch the pulse with a retriggerable
multivibrator at the other end if you need to transmit levels that
persist for very long.

Here\'s a way to use the commercial recievers:

https://spectrum.ieee.org/media-library/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNzIwNDE1OS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0MDMzODgzNX0._MPpSf8d-ldlNYWqvtD0hYtUcnjQTPio_Pw0MroGazY/image.jpg

U2-B output (with a pullup) should be what you want.

This is a really nice circuit for garage door safety beam, minimum
wires and designed so that DIY and numb-skulled installers can\'t
easily break anything or easily compromise the safety. Well, they
*can* do something like this:

https://i.imgur.com/p8QvQyk.png


--
Best regards,
Spehro Pefhany

 

[bitrex]

On 1/9/22 4:44 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 09 Jan 2022 22:32:46 +0100, Jeroen Belleman
jeroen@nospam.please> wrote:

On 2022-01-09 20:40, piglet wrote:
[...]

Not sure it\'s directly applicable to OP\'s problem but there was
this kinda cool circuit for increasing phototransistor tolerance to
ambient light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/


Interesting find! One old-school solution to that problem was to
operate the phototransistor into an inductor.

piglet


They want me to switch off my adblocker. Sorry, but no.

Jeroen Belleman

No loss. It\'s truly lame.

I wonder why some people design elaborate lowpass filtered negative
feedback loops to accomplish AC coupling. There are easier ways.

He wants to build a beam-break detector using a phototransistor for
whatever reason. I think there could be reasons to want to modulate the
transmitter with a linear signal vs. pulses but then you have to have a
way such that the phototransistor when connected as shown doesn\'t
respond to low frequency; how do you \"AC couple\" it when it has a
collector load as shown so that it don\'t pull down into saturation when
you turn on the room lights.

I don\'t think a photodiode has quite the same problem you can just bung
it into a TIA that doesn\'t have low-frequency gain, but that wasn\'t what
OP say he wanted to use.

For a beam-break across 2 feet IDK why you want a separate detector and
receiver anyway, why not put them in the same box and use a lil
parabolic mirror on the other side. FM a pilot tone and bounce it across
and back closing the PLL loop around that, when the phase detector goes
out of lock the beam is broken.

I think a missing-pulse detector could work also just driving with
pulses but then you gotta worry about how many missing pulses is an
actual break vs. maybe a glitch.

 

[bitrex]

On 1/9/22 2:40 PM, piglet wrote:

On 09/01/2022 7:32 pm, bitrex wrote:
On 1/9/22 7:33 AM, piglet wrote:
On 08/01/2022 7:51 pm, sonnic...@gmail.com wrote:
Hi all

I have played around with IR beams, and I wonder how to receive the
signal.
I just want to know whether my beam is broken. The system will at
the end work in a dark space. If blocked it will block almost
completely.

I tried with a phototransistor and a photodiode. I am using 890nm.
There is app 50 cm / 2 feet between transmitter (always on) and
receiver.

My question is on the receiver. I have tried to feed base or gate of
a transistor, with my phototransistor on the plus side, 10K to the
base/gate and 1M to ground.
The system works only within 5 cm or so. At 40 cm of distance, there
is only 0.07V on the resistor side (the 10K). In my room, with very
little light I get only a 0.02 difference whether my IR LED is on or
off.
On google I find example of a photo transistor feeding a normal LED
directly. Trying that at 12V still does not turn on my LED.
I have tried some phototransistors and one taken from a
sensor/optokobler (I cut it in half and used them with a bigger
distance)
Try my TV remote etc I get the same result, only a very week change.

The receiver is supposed to work on 3V or to batteries when ready.

Regardless of what I do I only get a weak change of 20-30mV. I can
move LED and phototransistor and clearly see a difference in angles
by a few mV.

Given that I work in a dark space, I could simple use a comparator
or opamp to boost the signal, simply look at say signal > 0.04mV.

How are other peoples experiences with IR receiving?
I work at a low voltage, so recivers for Ardoino is not really an
option. I and want the joy of working with this development

PS: I recall a friend many years ago using a 555 to send 2
frequencies for 0/1 and receiving it in the other end. Has anyone
done anything similar?


Are you doing this at DC with a the IRED continously on? You will
need a lot a gain at the receiver end and drift free DC gain is hard.
This is why almost all schemes use pulsed sources and AC
amplification at the detector. As a bonus the setup then ignores
slowly varying ambient light sources.

piglet


Not sure it\'s directly applicable to OP\'s problem but there was this
kinda cool circuit for increasing phototransistor tolerance to ambient
light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/


Interesting find! One old-school solution to that problem was to operate
the phototransistor into an inductor.

piglet

Digital seems like the right way to transmit data using an IR LED and
detector but I\'m not enamored of it for this one; it\'s a beam-break
detector not a garage door opener. I think a missing-pulse detector will
be fiddly..but a \"DC\" beam is also not the right answer.

With an FM loop so long as your detector doesn\'t saturate due to ambient
light/low frequency you can just amplify the crap out of your carrier on
receive and do a PLL-kind of thing, if your loop goes out of lock the
beam is broken.

 

[whit3rd]

On Sunday, January 9, 2022 at 11:40:37 AM UTC-8, erichp...@hotmail.com wrote:

On 09/01/2022 7:32 pm, bitrex wrote:

...circuit for increasing phototransistor tolerance to ambient
light:

https://www.edn.com/feedback-circuit-enhances-phototransistors-linear-operation/

Interesting find! One old-school solution to that problem was to operate
the phototransistor into an inductor.

There\'s also integrated cookbook solutions to the detect-only-modulation function.
Consider the venerable NE567 or LM567... discussed here
<https://www.homemade-circuits.com/lm567-tone-decoder-ic-features-and/>

I\'ve seen it used successfully, to make a sensor blind to ambient light, but
electronic ballasts and LED illumination and backlit monitors... we\'re in an
age where our ambient illumination comes with a lot of baggage.