Test LinuxCNC without motors and encoders connected

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03 Jul 2019 12:24 #138518 by Peterdeleu
With 5V I measure 3.5 V. While turning the encoder, I'm not able to read the output. It changes constantly.
But after I turned the encoder to the left or to the right, I see -3.7 or +3.7. But it is unpredictable. I mean.. after turning left, it could be + or -.
In de description of the encoder i could read that it is a incremental encoder. But I don't know what the difference is between incremental and differential....

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03 Jul 2019 13:18 - 03 Jul 2019 13:19 #138524 by andypugh

Peterdeleu wrote: But I don't know what the difference is between incremental and differential....


It seems likely that your encoder is both incremental _and_ differential.

An incremental encoder outputs a quadrature signal
AB
aB
ab
Ab
AB
and so on.

A differential encoder sends the signals as +ve and -ve differential voltages on two wires per phase

A+ B+
A- B+
A- B-
A+ B-

A single ended encoder sends the signal as 0V or 5V relative to ground on just one wire per phase

A5V B5V
A0V B5V
A0V B0V
A5V B0V

Depending on exactly where you stop turning the encoder you can see any of these states. So you would expect to not be able to predict the output when turning by hand.
Last edit: 03 Jul 2019 13:19 by andypugh.

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03 Jul 2019 13:33 #138527 by PCW
It looks like the outputs don't have much output current (< 7 ma) so have a hard time
driving the termination resistors on the 7I77, I would try single ended mode.

(Jumper the 7I77 for single ended mode and disconnect the /A,/B,/Z signals)

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03 Jul 2019 17:56 #138553 by Peterdeleu
I've tried single ended... but it didn't work.
I've applied 7V tot the encoder, (from the field power) Now it looks like it is working. :)
In "Show Hal Configuration" the hm2_5i25.0.encoder.00.count pin shows +-2000 counts/turn. This is probably the encoders 500 pulses multiplied by 4. (I bought I read that somewhere.. the count is pulsesx4)

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