Identifying and Using a Salvaged Optical Encoder

Thread Starter

kitare102

Joined May 26, 2020
1
Hi all,

I recently took apart a non-functional inkjet printer (Canon Maxify MB2320) and was left with some cool components. One of them was this integrated motor/encoder assembly:
The motor seems like a simple brushed DC, but the encoder has given me some trouble. I talked with an electrical engineer friend and this is what we've figured out so far:
  1. The I/O for the assembly goes over a 7-conductor ribbon cable
  2. Two of these conductors should be for motor power
  3. The surface-mount sensor unit has six pins and is broken up into two sections. Most likely: a 2-pin row for the LED and a 4-pin row for the detector(s)
  4. While the sensor unit does not have a common ground between LED and detector(s), their common ground is established by the PCB so that the 7-conductor ribbon cable is sufficient
  5. This leaves 3 other detector pins. We think the most likely configuration is for there to be two detectors to allow direction sensing (if this is obvious I apologize).
  6. That would mean the last three pins are common high voltage and signal 1 and 2.

I have all the wires to connect this assembly to the main control board, the PSU, and wall power. However, I have not been able to power on the main control board to allow me to probe the connections for useful information. My questions for you are:
  1. Is there something about the above reasoning that is flawed?
  2. Would you expect to have an easy way to jump power on with a control board like this?
  3. How do I identify what voltage to supply the LED?
  4. How do I identify which detector pins are which and what their outputs will look like?
  5. Are there other things you think I should know about trying to use this sort of assembly for my own purposes?

Thanks so much,
Eric
 

LesJones

Joined Jan 8, 2017
2,639
I think you are right that the two sensors are to give direction information. The two detectors will be positioned so they see light through the encoder wheel at slightly different positions of the wheel. This will produce signals with 90 degrees phase difference. The LED will be fed via a resistor from a power rail via a resistor. Start by finding this resistor and tracing back the circuit so you van find the voltage of this power rail. (I would guess this is probably +5 volts but you MUST confirm this.) The common of the two sensors could be connected to ground or to a power rail. Start by doing a resistance test to logic ground. Tracing the circuit from the other sensor connections should take you to the inputs of logic ICs or a microcontroller. There will probably be resistors biasing these inputs to a power rail but if they go to a microcontroller the inputs may be configured to use internal pull up resistors. If you are really lucky the opto device may have a part number and you can look for a data sheet for it.

Les.
 
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