IR transmitter and photodiode/reciever quetions - Page 1
Forum section: electronics / beginners

author: RobH
author_rank: Regular Contributor
timestamp: November 10, 2024, 04:28:45 pm
content: I have a few IR transmitter leds and 3 IR recievers / photodiodes, and built a simple circuit:https://www.instructables.com/Intro-to-IR-Circuits/The 1st circuit on that page.When I tried both IR transmitter and IR receiver none of them worked, in that the led D1 did not light up. I then tried again but in different order, and finally got a IR receiver and IR Transmitter to work.From that I assume that both transmitter and receiver must be paired, and the other transmitters etc were or would not pair.Now , after I removed the paired leds, I tried other transmitters with 2 other receivers. These did not seem to work, ie no led D1 light.I then replaced the 2 paired leds , but now the led D1 is on all the time, and that is the same with the 2 other receivers which would or didn't pair with the transmitter.So now I have 1 transmitter and 3 receivers which light up led D1 without and movement around them.I have replaced 1 IR transmitter which was paired with another and now what happens is that it seems to work in reverse. The led D is lit, but when I place my hand over the said leds , the led D1 goes dimmer.Any ideas as to why this is please.Thanks

author: PGPG
author_rank: Frequent Contributor
timestamp: November 10, 2024, 07:09:20 pm
content: Two info for you:- if D3 will be inserted reversed it won't shine,- if D2 will be inserted reversed it can make D1 on all the time, but if the 5V source is 'strong' the high current will go through D2 and Q1 b-e junction what can burn them (it could happened to your elements).

author: RobH
author_rank: Regular Contributor
timestamp: November 10, 2024, 08:51:22 pm
content: Thanks , but now I have found 1 IR transmitter , D3, which works or pairs?? with 3 IR receivers, D2, where the led D1 is now just on or lighting up, and when I move my hand over the top of both D3 and D2 , D1 lights up brighter.The problem? I have now is that the sensitivity range is next to nothing. I have to have my hand within about 5cms of D2 and D3 before any change in brightness is noticeable. I've added a 10k pot , but it doesn't make any difference

author: PGPG
author_rank: Frequent Contributor
timestamp: November 11, 2024, 01:43:09 am
content: Quote from: RobH on November 10, 2024, 08:51:22 pmSee this infrared detector:https://www.we-online.com/components/products/datasheet/1642730961200.pdfDistance is specified as 0.2 - 5mm.

author: RobH
author_rank: Regular Contributor
timestamp: November 11, 2024, 09:29:07 am
content: Blimey, 0.2 - 0.5mm is not much at all, but thanks anyway

author: PGPG
author_rank: Frequent Contributor
timestamp: November 11, 2024, 02:46:29 pm
content: Quote from: RobH on November 11, 2024, 09:29:07 amNot 0.5 but 5.It was to show you that 5cm you get is 'not so bad'.

author: RobH
author_rank: Regular Contributor
timestamp: November 11, 2024, 04:32:52 pm
content: Aah right then, 5cms. With what I have now is just about the same distance. I thought , wrongly maybe, that and IR transmitter had a range of more than 0.5 mtr

author: PGPG
author_rank: Frequent Contributor
timestamp: November 11, 2024, 06:32:21 pm
content: Quote from: RobH on November 11, 2024, 04:32:52 pmWhat do you have with this numbers?!You have written about 5cm.I have written about 0.2 - 5mmYou understood 5mm as 0.5mmSo I corrected that not 0.5 but 5.Now it looks that you think that 5mm is about the same as 5cm.Quote from: RobH on November 11, 2024, 04:32:52 pmI believe that using simple IR emitting diode and IR receiving diode I would be able to send signal for may be 20m. But doing it is not so simple as the circuit you use.

author: RobH
author_rank: Regular Contributor
timestamp: November 11, 2024, 10:57:06 pm
content: Ok, but is there any way that the range could be increased using a different circuit. I'm just curiousRegarding the distance figure you wrote this:Distance is specified as 0.2 - 5mm. but then corrected it to 5cm

author: PGPG
author_rank: Frequent Contributor
timestamp: November 11, 2024, 11:38:20 pm
content: Quote from: RobH on November 11, 2024, 10:57:06 pmNo I have written: 0.2 - 5mm.Then you have written:Quote from: RobH on November 11, 2024, 09:29:07 amI corrected your mistake writing that not 0.5 but 5.I didn't wrote anything about units as they didn't needed any correction - you have written mm what was correct.And suddenly you understand my 5mm as 5cm.Have you even looked into datasheet I linked. 0.2 - 5mm is from it so you could all the time just check it.Quote from: RobH on November 11, 2024, 10:57:06 pmIR detecting diode looks very wide so for it IRED diode is only a small point on the big area. It is like if you had totally frosted glass in the window and during day standing in the back of a room on the second floor trying to note if someone down on the street lights a cigarette.To detect small signal it have to have some specific feature you can use to filter it out from the background. Instead of lighting it with DC you can drive IRED with some frequency and then you have to build receiver with sharp filter of exactly that frequency. It is like radio receiver can receive only one radio station where there are lot of them reaching its antenna.