Bourns incremental encoders not really quadrature

[Dave]

Here I am, programming a microcontroller to read an incremental encoder for a circuit that I'm working on and wondering, why the state machine, that I coded for the encoder, isn't working as it should.

I coded the state machine to follow along as the signals A and B go high or low and added in a safety that throws an error if the state machine tries to skip a step in the quadrature. I flashed the code into the chip, expecting it to work as planned, but to my demise, it seemed to throw an error every time I turned the knob.

So I went ahead and looked at A and B signals on the encoder. Here's the interesting part:
As I ever so slowly turned the axle clockwise, both A and B were pulled to ground in the exact same moment and only jumped up one after the other.

So instead of this (taken from the datasheet),


what I really have is this.


Now I know that it still outputs a signal which can be used for detecting rotation and direction, but this isn't the point. The datasheet says the signal is quadrature, but there are only three different states which can be found on the output.
Just to make sure that I'm not crazy (and because I happened to have a spare), I decided to check the other one as well. Same story.
Does anyone have an idea what might be going on? I bought these encoders directly from Mouser, so I don't think they are counterfeits (they look and feel pretty solid).

The exact part number is PEC16-4120F-N0012.

[rs20]

I think you've got your wiring wrong. If you have the wrong pin on your encoder wired as the "common" pin, it'll end up outputting A and (AB), not A and B. Which is consistent with what you're seeing.

[Dave]

I think you've got your wiring wrong. If you have the wrong pin on your encoder wired as the "common" pin, it'll end up outputting A and (AB), not A and B. Which is consistent with what you're seeing.

I'm an idiot.

But you can see how this confused me.


Welp, time to pull out a knife and make my PCB look like shit.

There, mystery solved. Nothing to see here.

[T3sl4co1l]

1. Because
3. Sense.
2. this makes

Tim

[Fungus]

So I went ahead and looked at A and B signals on the encoder. Here's the interesting part:
As I ever so slowly turned the axle clockwise, both A and B were pulled to ground in the exact same moment and only jumped up one after the other.

Not possible. Nothing would work with them.

Check results again.

I'm an idiot.

We've all been there! 

Difference: Idiots don't learn from mistakes.

mystery solved. Nothing to see here.

 

[Refrigerator]

1. Because
3. Sense.
2. this makes

Tim

I guess they hired Yoda to make that PDF.

[Dave]

I feel like I owe you guys some post-bodge pics.

She does work as expected now. The state machine works like clockwork.