HEDS-5500:: weird index?

[0db]

so a collegue gave me yesterday an ARM board (probably derived from Odrive?) which has the HEDS-5500 incremental encoder, and asked me to give an eye to it because apparently the firmware doesn't work correctly.

The first thing I did this mornign was attaching the incremental encoder to a LA, to have a look.

The HEDS-5500 has three signals
- channel A
- channel B
- index

The index output is a 90 electrical degree, high true index pulse which is generated once for each full rotation of the codewheel.



But ... look at the screenshot: the index signal is always equal to channel B ... I wonder why?!?

I have already tried two of these encoders. Always the same result.

[dmendesf]

From the datasheet:

For the HEDS-5500 and HEDM-5500, Pin #2 is a No Connect.
For the HEDS-5540 and HEDM-5540, Pin #2 is CH. I, the index output

[0db]

No connect, but there is a signal on that pin #2. A copy of the channel B.
I think someone must have shipped the wrong couple of encoders with the kit.

[dmendesf]

Seems so. "No connect" isn't the same as "not connected"...

[H.O]

And you are sure the signal is actually there, it's not crosstalk between channels on the LA due to the index channel actually floating?

[0db]

And you are sure the signal is actually there

Yes, it's really there, on the 4th channel of the LA. I see it even if I remove both the ChA and ChB of the encoder.

And since it's really there, this was the reason why the Odrive controller didn't work: because in autocalibration mode it assumed the encoder had an index, since the firmware actually saw some signal on the Pin#2.