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?
IR phototransistor reciever
Started by ●January 8, 2022
Reply by ●January 8, 20222022-01-08
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
Reply by ●January 8, 20222022-01-08
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
Reply by ●January 8, 20222022-01-08
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.
Reply by ●January 8, 20222022-01-08
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
Reply by ●January 9, 20222022-01-09
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
Reply by ●January 9, 20222022-01-09
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.
Reply by ●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
Reply by ●January 9, 20222022-01-09
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 ●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 >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/>