help needed with analyzing a salvaged photo-interruptor.

Thread Starter

Isaac Crockett

Joined Mar 22, 2018
2
I salvaged this photo-interruptor out of an HP photocopier. I want to use it to measure distance traveled on a small robot by detecting breaks in wheel passing through it, but I am having diffculty identifying the positive, negative, and output leads. Any help with this would be most appreciated.IMG_20180322_213755679.jpg IMG_20180322_213825137.jpg IMG_20180322_213755679.jpg IMG_20180322_213825137.jpg
 

theodoravain

Joined Mar 21, 2018
34
I salvaged this photo-interruptor out of an HP photocopier. I want to use it to measure distance traveled on a small robot by detecting breaks in wheel passing through it, but I am having diffculty identifying the positive, negative, and
output leads. Any help with this would be most appreciated.
If there's no onboard encoder chip (I don't see one) you only need to know that the emitter and detector are an IR LED and a PD respectively with corresponding voltage drops. Sometimes the detector is a base-floated PT. You can ID them with a DMM on junction-check.
 
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Thread Starter

Isaac Crockett

Joined Mar 22, 2018
2
When I noticed the diode symbol on the left side (more accurately realized what that symbol means) I figured that out. Unfortunately, I have no DMM. just ordered one from Amazon but I'm very impatient.
I'm figuring that the leads off of the photo-interruptor which are combined are the negative leads, the other on the side with the diode symbol would be the positive lead for the ir LED, and the remaining the positive lead for the PD.

(I am brand new to electronics, jumped into this project about three weeks ago.)

IMG_20180316_222435956.jpg
 
It's fun, economical and educational to salvage parts. Do you want to remove the slotted optocoupler or try to draw out the circuit?

A couple of suggestions. Take a look at a sample of the number of varieties of slotted optocouplers here https://www.digikey.com/products/en/sensors-transducers/optical-sensors-photointerrupters-slot-type-logic-output/547

The manufacturer thoughtfully put the diode symbol on one side, so you have a pretty good idea of half of the connections figured out - but you will need to do a little investigating to figure out the other side - that's where looking up the resistors and capacitor values and trying to draw out the circuit might help a lot.

What do you think is on the connector - +V in, GND and pulse out?

It was probably used as an endstop - see here for some help https://capolight.wordpress.com/2010/11/24/making-endstops-from-printer-photo-interrupters/

For your uses (getting distance from speed measurement) - take a look at this project https://create.arduino.cc/projecthub/mitov/measure-motor-speed-rpm-with-optocoupler-and-encoder-disk-c3a0e4

Have fun and let us know how things progress.
 

theodoravain

Joined Mar 21, 2018
34
the other on the side with the diode symbol would be the positive lead for the ir LED, and the remaining the positive lead for the PD.
About the symbol, the back of the arrowhead is the anode, the line is the cathode. The junction is forward biased when the anode is >= one forward drop more positive than the cathode. The Forward drop can be 3 volts or more with some LEDs. Be sure to limit the current to a safe level with a ballast resistance.
In my opinion the diode symbol indicates the emitter LED. Photodiodes are fast but deaf. Shaft encoders aren't speed intensive so the detector is probably an npn phototransistor C-positive, E-negative, B-floating (light activated).
 

theodoravain

Joined Mar 21, 2018
34
It's fun, economical and educational to salvage parts. Do you want to remove the slotted optocoupler or try to draw out the circuit?

A couple of suggestions. Take a look at a sample of the number of varieties of slotted optocouplers here https://www.digikey.com/products/en/sensors-transducers/optical-sensors-photointerrupters-slot-type-logic-output/547

The manufacturer thoughtfully put the diode symbol on one side, so you have a pretty good idea of half of the connections figured out - but you will need to do a little investigating to figure out the other side - that's where looking up the resistors and capacitor values and trying to draw out the circuit might help a lot.

What do you think is on the connector - +V in, GND and pulse out?

It was probably used as an endstop - see here for some help https://capolight.wordpress.com/2010/11/24/making-endstops-from-printer-photo-interrupters/

For your uses (getting distance from speed measurement) - take a look at this project https://create.arduino.cc/projecthub/mitov/measure-motor-speed-rpm-with-optocoupler-and-encoder-disk-c3a0e4

Have fun and let us know how things progress.
Dude! I wish there'd been teachers like you where I grew up!:cool:
 
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