# [SOLVED] Determine which pins are output/ground/Vcc on 3pin ir detector



## geosman (Sep 15, 2007)

I have some IR detectors in my junk drawer and need one to use to trip a relay via a 555.
I have spent time reading from my searching to find how to do this but am tired of reading the snide snarky remarks like just go buy a new one or where did u find that in a supermarket. 
Anyway, my need is: how does one use a multimeter (Ohms scale or Diode test) to determine which is the collector (power), base (signal) and emitter (ground) of 3 pin IR detectors? 
The explanations I have read all end up leaving me unsatisfied as the tests seem to contradict themselves or do not find the base(signal) initially.


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## Mijoker (Oct 8, 2013)

*Re: Determine which pins are output/ground/Vcc on 3pin ir detector*



geosman said:


> I have some IR detectors in my junk drawer and need one to use to trip a relay via a 555.
> I have spent time reading from my searching to find how to do this but am tired of reading the snide snarky remarks like just go buy a new one or where did u find that in a supermarket.
> Anyway, my need is: how does one use a multimeter (Ohms scale or Diode test) to determine which is the collector (power), base (signal) and emitter (ground) of 3 pin IR detectors?
> The explanations I have read all end up leaving me unsatisfied as the tests seem to contradict themselves or do not find the base(signal) initially.


 
I did a quick search based on your verbage and found this: 
VISHAY-Infrared-Receiver-Modulecopy.jpg Photo by audioslayve | Photobucket

this picture shows the "IR+", "Common -" and "5v DC" 
I hope that helps!


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## Fjandr (Sep 26, 2012)

*Re: Determine which pins are output/ground/Vcc on 3pin ir detector*

From circuit - How do I know if which leg is the emitter or the collector? (Transistor) - Electrical Engineering Stack Exchange

```
Set meter to lowish ohms range so a diode conduction can be seen - trial and error OR diode test if available.

With an NPN transistor the base will have two diodes facing away from it. ie with most positive meter lead on the base the other two leads will show a conducting diode when the negative lead is placed on them

With a PNP transistor the base will have two diodes facing towards it. ie with most positive negative (usually black) meter lead on the base the other two leads wil show a conducting diode when the positive lead is placed on them

OK - now you know NPN from PNP and which is base. Now

Connect positive to guessed collector for NPN and negative to guessed emitter. Set meter to 1 megohm plus range.

-Connect base to guessed collector via a high value resistor - probably 100k to 1M. A wet finger works well. Note reading.

Now swap guessed emitter and collector and repeat. Again resistor is added from base to guessed collector. Note reading
One of the two above will have a much lower R_CE reading when base is forward biased. That's the correct guess.

Once you get used to this you can pick up a leaded transistor, juggle it with meter leads till you find the two diodes giving base and NPN or PNP then lick your finger and do a forward bias base test - and then declare pinout. Looks like magic to many. Works.

You can or course formalize that on a breadboard and even add (gasp) switches to swap polarity etc.

Note that you can get some idea of Beta (current gain _ from this once you learn to calibrate your wet finger.
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## geosman (Sep 15, 2007)

*Re: Determine which pins are output/ground/Vcc on 3pin ir detector*

@Fjandr: U have the beginning of what I was looking for.
Would it then be correct to say that for a PNP transistor in the second phase of the test using a high resistance that the probes are reverse of what you described for the NPN?


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## Fjandr (Sep 26, 2012)

*Re: Determine which pins are output/ground/Vcc on 3pin ir detector*

If you place the negative lead onto the base, it should register voltage flow through both other pins if it's PNP.

An NPN will register voltage flow when the positive lead is placed on the base and the negative on either of the other leads.


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