This is the deal i found the part don't no where but it had a IR diode and phototransistor
I'm trying to figure how they was using it.
Here is how its made p1 is VDD i didn't have led or phototransistor npn is p3 the base.
led is d1 and p2 is ground.

They seem to be reading the base voltage.

 

Here the board you can see the output is coming from the base.

 

Are you sure that the transistor is just a transistor and not an integrated circuit which amplifies/processes the photo-transistor signal?

 

Is it a slotted opto-switch?
What does the other side look like?

 

could be an IR receiver for remote control. try a square wave carrier - 36 khz to 56 khz.

 

could be an IR receiver for remote control. try a square wave carrier - 36 khz to 56 khz.

But then why would it have the LED?

 

Could be a IR receiver and IR TX?

When the circuit works as IR TX:

• Drive P1 and P2 with 38KHz etc to send stuff.
• Ignore P3

And when the circuit works as IR RX:

• P1 = VCC, P2=GND, P3=OUTPUT

 

It has 3 wires Vdd and ground for the led I didn't have the parts to show that so I used a diode for the led
and npn for the phototransistor.
The phototransistor is hooked to the power that feeds the lR Led.
I powered it up the IR led is on when I block the base changes.
But it's giving crazy readings.

 

It certainly looks like it is designed to be a slot opto switch but it is very wide.
I guess one of the problems is that you don't know what supply voltage it expects.
Is there any identification on the three legged device?

 

I took the cover off for the picture
But it's powers the it led I can see it with my phone.
But what I can figure out is why they are using the middle pin of the phototransistor which is the base to read ticks on the disk I'm thinking 5 volts not what it was using

 

Guess I'll forget getting that to work I got 100 of these laying around but that one was the first 3 pin I seen i just burnt out the IR led with 10 volts

 

If they run the base to the input of a transimpedance amplifier they probably got more sensitivity and bandwidth using the transistor as a photodiode than as a phototransistor.

 

Thanks I'll read up on that transimpedance amplifier I tested it with a arduino adc pin It was giving reading's
stepped the voltage up on the Ir led cause 5 volts seemed low with the 360 resistor I killed the Ir led It only came on and went off end of that one I got a bunch Of these not marked out of old stuff.

 

I suspect your phototransistor is something more complicated than just a transistor.
Something like this: https://uk.rs-online.com/web/p/slotted-optical-switches/4550868/

 

Dont think this is like that one but I have some that are.
It's clear case you can see there's nothing in it but the end of the pins it maybe still good tho just killed the or diode