# 7i77 and single ended MPG-Wheel encod er - read-out problem

22 Oct 2021 19:07 - 22 Oct 2021 19:08 #223944 by PCW
OK those are good values on S0 ( A )
the next question is does S90 ( B ) go low
at some position?
( This would be expected to happen about
1/2 way between the "normal" and "between normal"
positions )
Last edit: 22 Oct 2021 19:08 by PCW.

22 Oct 2021 19:42 - 22 Oct 2021 19:45 #223946
hm... you mean B (S90) shoud behave like: 200mV - 0V - 4.06V while turning ?
I'll try to figure it out tomorrow. Right now, it seems to me, that it just "jumps" from200mV to 4.06V - the same for A (S0) just in opposite way

Edit: I just saw my stupid typo in my last post!
It should be:

"Between normal" (between slots):
GND - S0: 4.06V
GND - S90: ca. 200 mV

I'll try to edit my last post...
Last edit: 22 Oct 2021 19:45 by Baderbahn.

22 Oct 2021 19:45 - 22 Oct 2021 19:51 #223947 by PCW
If A and B swings from ~4V to ~0V then the 7I77 encoder should count
if the phase difference between them is 90 degrees:
```----____----____----____
--____----____----____----```
Last edit: 22 Oct 2021 19:51 by PCW.

22 Oct 2021 19:47 - 22 Oct 2021 19:49 #223948
Hm...
Before I left my workshop half hour ago, I tried again, with the encoder wired as single ended one to the 7i77s encoder input - did't count according to halshow (rawcounts)
Is there a possibility to see the values, which the card is meassuring on the individual input-chanels of the encoder input-plug?
Last edit: 22 Oct 2021 19:49 by Baderbahn.

22 Oct 2021 19:53 - 22 Oct 2021 20:00 #223949 by PCW
You can read (and plot with halscope)  the digital values on the encoder input-a and input-b pins
Last edit: 22 Oct 2021 20:00 by PCW.

22 Oct 2021 19:59 - 22 Oct 2021 20:01 #223951
Ok, I'll try again tomorrow.
I also had them on halshow but never was able to see them flickering :/

Thank you very much for your help so far!

P.S. I everytime put all encoders on halshow to ensure, that I don't check the wrong chanel
Last edit: 22 Oct 2021 20:01 by Baderbahn.

23 Oct 2021 12:53 - 23 Oct 2021 12:55 #223985
Now it's getting weird...

The yesterday meassured values where meassured with A / B unplugged from the 7i77 and just powered up by the card's encoder output.

Now I plugged A / B into the card and can see a/b - Signal in halshow - they are constantly there.
I meassured again while connected: Constantly 4V from GND to A/B (S0/S90)! As soon as I unplug A / B from the card, I have the same quadrature signal as described yesterday.

I think, It can't be an card issue as I tried the Encoder-Input with an (differential) linear encoder to ensure a working encoder-chanel

And yes, I change the jumpers between differnential / single-ended.
Last edit: 23 Oct 2021 12:55 by Baderbahn.

23 Oct 2021 15:01 - 23 Oct 2021 15:02 #223993 by PCW
Is the 5V from the 7I77 OK? Low 5V would make the LEDs dimmer

The MPG A,B outputs are probably just the LM393 comparator outputs
with pullup resistors to +5V, so I would expect a full 5V signal swing

When plugged into the 7I77, the 7I77 adds an additional 2K pullup
resistor to 5V on each signal which should be OK since the LM393
can sink 6mA minimum and about 20 mA typical
Last edit: 23 Oct 2021 15:02 by PCW.

23 Oct 2021 15:30 - 23 Oct 2021 15:34 #223995
I have 4.75V 7i77 output voltage and 4.1V between GND and A/B when A/B are connected to the card.
Basically, the output voltage seems to  be enough, as i have a swinging signal, when not connected to the card:
As soon as I unplug A/B, I have the same meassuring results from yesterday evening.

There are some BC327 transistors, prior to the output.

I already dismounted the transistors and checked them, they are fine.

P.S. maybe, I need "real sinking" inputs without the pullup resitors ? - just a thought...
Last edit: 23 Oct 2021 15:34 by Baderbahn.

23 Oct 2021 15:34 - 23 Oct 2021 15:36 #223997 by PCW
Ahh if they have PNP transistor outputs, the MPG has sourcing
outputs so would need a stiff pulldown resistor to work with the
7I77 encoder inputs (say 330 Ohm)

They should work directly with the 7I77s MPG inputs
(since those are sinking inputs)
Last edit: 23 Oct 2021 15:36 by PCW.