Basic distance emitor and receiver circuits

bertus

Joined Apr 5, 2008
22,270
Hello,

The little bag of PD638C photo diodes do not match IR:
PD638C_spectral sensitivity.png
The sensor would be good for the lower part of IR-A:
AbbreviationWavelengthFrequency
IR-A700 nm – 1,400 nm
(0.7 μm – 1.4 μm)
215 THz – 430 THz
IR-B1,400 nm – 3,000 nm
(1.4 μm – 3 μm)
100 THz – 215 THz
IR-C3,000 nm – 1 mm
(3 μm – 1,000 μm)
300 GHz – 100 THz
https://en.wikipedia.org/wiki/Infrared

Bertus
 

Thread Starter

q12x

Joined Sep 25, 2015
1,658
The little bag of PD638C photo diodes do not match IR:
The sensor would be good for the lower part of IR-A:
AbbreviationWavelengthFrequency
IR-A700 nm – 1,400 nm
(0.7 μm – 1.4 μm)
215 THz – 430 THz
IR-B1,400 nm – 3,000 nm
(1.4 μm – 3 μm)
100 THz – 215 THz
IR-C3,000 nm – 1 mm
(3 μm – 1,000 μm)
300 GHz – 100 THz
https://en.wikipedia.org/wiki/Infrared

Bertus
Thank you mister @bertus !!! for checking this out. While in the night, in my room, while the windows are covered, in complete darkness and that sensor (PD638C) is fully open (when it should stay closed) . I don't like it because it stays open all the time, even in the most dark room. All the tests I did on it was with visible light !!! (and it turned out to be IR and polarized ) That's why I thought it must be for other types of light wave lenght like IR perhaps. I did try with a remote control on him just now, and it was a little catch to it, it's polirized, meaning its having a + and a - pins. But they are inversed, the short one is + and the longer one is -. I took a telecomand for TV, test it first with my phone camera, and it showed the light from it. Then I tested these PD638C and they worked. I did test a bunch of other ordinary foto sensors i have, foto - diodes(a couple) and transistors (i have 1), and they all switched (It even show the interrupted signal) from the IR light signal of telecomand. Only the foto-resistors did not respond to the IR light. Very illuminating experiment , for me. Thank you for your help so far. The problem is that all the sensors I have, I must put the IR led directly on them or super close (5mm) to them to see the telecomand signal. They work somehow from a reasonable distance as well, like 10cm, but the signal is very faint. Probably is my receiver test circuit not that sensitive and not that calibrated. I built it to test normal LDR's and the grade of sensibility of each i have. That must be it for certain. I also test this PD638C in direct super bright light from a lamp i have on my desk, very close to the bright leds, and in the same time I expose it to the IR and it is working only for IR and not for the normal super bright light. That is very good to know. Thank you all for your help !
Probably before, when i made the first tests on these new PD638C, I didnt thought they have inversed pin polarity, and all my tests failed so I did not know whats with them for sure.
 
Last edited:

AlbertHall

Joined Jun 4, 2014
12,345
They work somehow from a reasonable distance as well, like 10cm, but the signal is very faint. Probably is my receiver test circuit not that sensitive and not that calibrated. I built it to test normal LDR's and the grade of sensibility of each i have.
What circuit did you use?
 

BobTPH

Joined Jun 5, 2013
8,813
IMHO, you are wasting your time trying to do this with a photodiode. The IR detectors used in TV remotes have serious electronics as well as the IR filter built in. Surely you can find a junk TV and remote somewhere and get the sender and receiver you need.

Bob
 

Thread Starter

q12x

Joined Sep 25, 2015
1,658
The circuit is not capable to support the photo diode PD638C that is used.
Yes, it supports it very well. The problem is the sensitivity, which mister @AlbertHall give me a solution already with his link.
It even supports all sorts of photo-diodes,-transistors,-resistors. And is a formidable tester. I even test the "almost" complete burned, but slightly working ones as well. That good it is. :]
But is a tester and is only telling me if the component is good or bad. It is not made for performance, like long distance or other special characteristics.

Yes, the phototransistor will not get to a very low resistance like an LDR will so you need more gain between the phototransistor and the relay, perhaps like the link below.
https://electronics.stackexchange.com/questions/37805/phototransistor-dark-detector-circuit
...
Aha, it's a pin diode not a phototransistor. However, the principle point is the same - more gain required for more range.
I will try this circuit you are suggesting for this PIN foto-diode PD638C and check its range. Very nice to mention about the gain thing, that I am still learning/experiment it, from my previous temporary goal with opamp that i stopped and concentrated on current one, but I will get back to opamp after finishing this first. The problem right now is that I dont have a IR led whatsoever. So I am waiting for the package to arrive (IF it will arrive).
 
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