Been hacking old mechanical mice and they have optical rotary encoders. The typical phototransistor is a 3-pin device which is a dual common collector phototransistor. Based on some ap notes and specs I figure that power is applied to the middle pin and the two legs are connected to gnd through 10K resistors. When I power up the IR emitter diode, I get about a .3V drop (no IR is about a .003V).
I've tried changing the resistor, increasing the current of the IR emitter, adding the resistor to the collector and I cannot make the phototransistors go into saturation (should get ~VCC with IR on).
Anyone has experience using these phototransistors? ... Thanks...
WHat voltage can you get when the phototransistor is illuminated? Have you tried visible light or infra-red? I think most mouse-type phototransistors are IR-sensitive and possibly block visible light. Are they in transparent packages or in dark packages?
I read about .3V when the phototransistor is illuminated with the IR emitter in the opposite side. If I power the IR emitter, I read 3 mV. If I shine the halogen bulb (my desklamp) really close, i get 1V. In theory I expect ~5V as the phototransistor is supposed to be fully on in saturation mode. The phototransistor are in dark packages. I was reading this application note: Intelligent Power and Sensing Technologies | onsemi
They're probably only sensitive to infra-red, then. Your halogen desk light must put out a lot of IR! To get closer to 5V, you could try increasing the pull-down resistor to 22k Ohms, 47k Ohms or even 100k Ohms. Try a few different values and see what happens.
I figure that power is applied to the middle pin and the two legs are connected to gnd through 10K resistors.
If that were correct then you should see no (or a low) voltage when there is no IR light and a high voltage with IR light. The swing is right but there is not enough of it. Therefore you do not seem to be pulling enough current through the photo transistor to get a voltage change.
Therefore I would change those 10K resistors to at least 100K or maybe even 470K. In that way a smaller current swing gives a larger voltage swing.
I came a cross mouse with 3-pin photo detector, 1 pin go to ground, middle pin to +5V and the other pin connected to input of device without resistor. You may try it out.
I once checked mouses, and I think optosensor went directly to a chip. I was 0---5V levels.
Your mouse may be different but you may light leaking, like others have said. But are you sure your voltages are right way. It could be low voltage when there is light and high when there is no light. But check leaked light.
I came a cross mouse with 3-pin photo detector, 1 pin go to ground, middle pin to +5V and the other pin connected to input of device without resistor
I think this is how it was wired in the mouse. But if one side is grounded then how would it sense direction? In other words, I was hopping to get quadrature coding out of these devices.