Quad Encoder Problem

[RossWaddell]

But if the interrupts are meant to fire on either a rising or falling edge, then going from '00' to '10' has only one edge (A rises from 0 to 1; B stays the same). The 00 to 10 state change represents one detent, right?

I got this ISR code from another post (http://www.picbasic.co.uk/forum/show...5396#post25396) and it seemed to work back then (incrementing MotorRPM by 1)

[HenrikOlsson]

Hi,

But if the interrupts are meant to fire on either a rising or falling edge, then going from '00' to '10' has only one edge (A rises from 0 to 1; B stays the same).

Yes of course, one edge.

The 00 to 10 state change represents one detent, right?

It depends on the encoder used but most mechanical type encoders I've come across has a full quadrature cycle per detent. Here's cutout from the datasheet for a EN12-series encoder from TT Electronics:



As you can see, going from one detent to the next results in a full quadrature cycle or four edges. So if the IOC is setup to trig the on the rising and falling edge of both the A and the B input then you'll have four interrupts per detent so the MotorRPM variable will increase by 4.

When it "seemed to work back then" was that with this very same encoder or have you changed it? Do you have a modelnumber or datasheet for the encoder you're using?

/Henrik.

[RossWaddell]

Quite possibly it was using an earlier rotary encoder. I switched to a CUI ACZ11 (datasheet) one because I needed the button. Perhaps the Grayhill one I was using before (datasheet) showed the single-increment-per-detent. The CUI datasheet doesn't explicitly state it goes through a full quadrature cycle but one of the diagrams seems to infer that.

Again, thanks for your patience, Henrik. Your explanation makes sense to me now (I hadn't realized that different mechanical encoders behave differently. Should have checked that, of course).

EDIT: I just replaced the CUI encoder with the Grayhill one on my breadboard and guess what - it increments by 1. Mystery solved. Sadly, there doesn't seem to be a cheap Grayhill encoder with a push button so I'll just have to add comments in case I ever switch encoders again to do this test (or read the data sheet more carefully).

[HenrikOlsson]

Hi,
The CUI datasheet shows that for models 12C and 20C it's full a cycle (4 counts) per detent while for the 15P30 it's half a cycle (2 counts) per detent. It's a bit misleading that they state for example, 12ppr, 12 detents when it's actually 12cpr, 12 detents.

The Grayhill datasheet explicitly says 1/4 cycles (1 count) per detent.

So, yes, "problem" explained/verified.

/Henrik.