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
IR phototransistor reciever
Started by ●January 8, 2022
Reply by ●January 9, 20222022-01-09
Reply by ●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 ●January 9, 20222022-01-09
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 BellemanNo 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 ●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.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
Reply by ●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 ●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 ●January 10, 20222022-01-10
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.
