Has anyone ever seen one of these? Three channel "Rotary Encoder" from a VCR's PCB.

rwgast_logicdesign · 2012-12-18 11:07

So last night I was just scrapping parts, specifically input devices for a controller. Walked away with a few joysticks and rotary encoders. I ended up desoldering something I thought was a rotary encoder but im not so sure what it actually is. It came out of a VCR I think, and the pins were labled ground, Channel A, Channel B, and Channel C. I thought it was strange there was no power pin labeled. I brought it in hooked it up to a logic analyzer and couldn't get it to work, It seems as though anywhere I connect power to it causes it to short out the supply when I turn the knob! I then looked at the back and saw the crazy design on each of the three channels, realizing it wasnt just a quadrature encoder with a weird pin label I thought Id ask if anyone has seen one before, and if so why would it be on the PCB of a VCR?! It wasn't mounted in a way where the user could turn it, im not sure maybe the motor use to turn this device or something.. Hope I can someone can tell me how it works and maybe I can come up with a use for it sense I took time out of my night to de-solder it, lol.

I also pulled a mechanical quadrature encoder from a mouse wheel and some joysticks off an x-box controller, should all this stuff be mostly compatible with the parallax code for there joystick and rotary encoder?

Circuitsoft · 2012-12-18 11:16

Hook pull-ups to the three channels, watch three channels on the o-scope, and turn it to see what it does.

Don M · 2012-12-18 11:27

Having been one who has worked on VCR's for quite a number of years for a living, what you have there is called a "mode" switch. What you'll notice is that it has contacts of differing lengths. It is made to interact with a rack and pinion or linear gear to make contact at various strategic points in a "cycle" of operation.

Many manufacturers went to this when they started using a single "mode" motor to operate the loading, unloading, FF, REW & Play functions. It would indicate when the mechanical parts are in their correct position.

John Abshier · 2012-12-18 12:14

Possibly a quadrature encoder (A & B channels) with the C channel being an index channel, 1 pulse per revolution.

John Abshier

rwgast_logicdesign · 2012-12-18 13:43

Well thank you don. So this thing is pretty useless? Its a custom patteren which is probablly not to usefull correct?

Don M · 2012-12-18 13:57

Most likely it would be useless to use as a rotary encoder.

rwgast_logicdesign · 2012-12-18 14:27

how exactly could i power this thing and read it with a logic ananlyzer? as i mentioned theres only a groung and three channels, if i apply voltage to any of the channels it causes shorts. Someone earlier mentioned a scope which i dont have. I just wanna play with it maybe find a use for it, its just intresting. im thinking you ground it and pull up the three channels as mentioned earlier.

Don M · 2012-12-18 14:50

If you wanted to read it with a logic analyzer I would connect the common to +5V and then connect each of the other 3 pins each through a 1K resistor to ground. Connect your 3 logic analyzer channels to the junction of each switch lead and resistor. Connect the common of the logic analyzer to ground. You should then be able to spin the switch and see what it"s "signature pattern" looks like. You'll need to spin it in one complete revolution at as constant speed as you can. You might even chuck it in a cordless drill to get a nice constant spin motion at a slow speed.

Just my .02...

Edit: The only potentially bad thing might be any dirt or poor connection of the switch contacts you'll get some glitches in your traces.

Has anyone ever seen one of these? Three channel "Rotary Encoder" from a VCR's PCB.

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