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.
Reply by bitrex●January 10, 20222022-01-10
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.
Reply by bitrex●January 10, 20222022-01-10
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.
Reply by Spehro Pefhany●January 9, 20222022-01-09
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.
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
Reply by Jeroen Belleman●January 9, 20222022-01-09
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
Reply by piglet●January 9, 20222022-01-09
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
Reply by bitrex●January 9, 20222022-01-09
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
>
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
Reply by piglet●January 9, 20222022-01-09
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