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

Hello Guys,

recently, I wired up my original DECKEL MPG-Wheel and conected the Encoder to the cards as described below:

Wired to TB4 / Encoder-Port of the 7i77 - in brackets you'll find the names on the Deckel encoder-board:
QA3  to A (S90)
GND  to 0V (0V)
QB3   to B (S0)
+5V   to +5V（UB)

I am able to read out the signal with my normal oscilloscope, the signal-peaks are at ca. 0.2V.

Sadly, I'm not able to read out the counts by halshow - neither the rawcounts nor a- and b- signal.
I tried to jumper it in both ways - single ended and differential but nothing works.

Maybe the difference  between the Signals is too small?

I'm sure, you have some ideas on how to solve this issue

Thanks and best regards,
Simon

You need at least TTL levels for the single ended 7I77 encoder inputs to work
that is > 2.4V for a high level and < 0.8V for a low level

0.2V sounds like there may be a wiring issue or you have the 7I77 jumpered
for differential inputs.

I think that is too low.  I usually use the dedicated MPG inputs on the 7i77 for 100 count 5v mpg. See page 18 in the 7i77 manual.

Hello PCW,

thank you for your reply!

I just meassured with the scope again:
Meassured between GND and A or B:
Quadrature signal is ca. 0.5V above / below base-level. Base-level between GND and A/B is 4.1V - leads to high peak at 4.6V and low peak at 3.6V
A and B are similar, just 90° shifted

will it help to bridge GND to /QA and /QB and use differential mode ?

P.S.
I did't recognize OT-CMCs message: I'll try this maybe, but first I need to change the allready wired inputs to another input. Also, I need to check, how to change to mode 3 - but I recognize some threads about that, where I can search for this toppic.
But prior to rewiring, the questions is: will the peak-level be enough to detect the signal ?

A and B low levels need to be below 0.8V and high
levels need to be above 2.4V

1. Is the 7I77 encoder input you are using jumpered for TTL (single ended) mode?
2. Have you checked your wiring? both A and B always high (>2.4V)
sounds like a missing ground connection

Hello PCW,

attached, you will find a picture of the encoder-pinout - the wiring there is the original one - I've got the wheel from an deckel-mechanic few years ago.

To 1): The Jumpers close to the connector are in left-handed position, so it must be single-ended mode, according to the manual.

To 2): I doubblechecked the above mentioned values by unplugging it from the 7i77 and powering up the encoder with an external power-source.
If I connect the scope to 0V and A or B and turn the crank, I can see a beautifull quadrature signal - with the above mentioned base-line at 4.1V and high-peak / low-peak ~0.5V above/below
I have no idea, where there should be a additional ground connection... The Encoder, encoder- housing, computer, etc. even share earth.

Maybe I wired the encoder in a wrong way ? But how I should wire it instead. The way I wired it up (reffer to post 1) is the only way, wich makes sense to me - and I think, I'm basically right, due to what I can see with the scope.
If it helps, I can make a picture of the scope's screen on friday.

Just for information:
The encoder itself is equipped with 2 IR-SMD LEDs and the corresponding photo-cells, together with a LM393P comparator and a slotted wheel to trigger the LEDs

Yeah, those are not valid levels, the LM393 should have outputs
very close to ground (< 0.5V) when low.

You might try cleaning the LEDs and sensors or adjusting
the threshold if there's a potentiometer on board.

Hello Together,

I tried to clean the LEDs and Sensor, but no real success. The peak levels are slightly higher now.
If I meassure with the scope between A and B (S0 and S90), I have pretty nice quaddrature peaks (with at least 5V peak-peak) - so its maybe a 2-wire differential encoder?
I tried to wire both to "A" and jumpered as differential encoder on 7i77, but still no success.

Now I rewired the other Inputs of the 7i77 and can use Input 16-19 for the MPG encoder. I rewired A and B (S0 and S90) to these connections allready.

Also, I changed the software- mode to mode 3 by [...] sserial_port_0=003xxx[...].

But I'm not sure, how to wire Input 16 and 17 in HAL.
I found another thread " How to wire MPG on 7i77 " but I'm not really sure, how to use the file there.
I use the PNCconfig- generated MPG-file right now and it seems to work well (according to HALshow) except the encoder.
So maybe you can help me to wire Input 16 and 17 to the PNCconfig  generated MPG section.

Thank you very much in advance and best regards,
Simon


 

Unfortunately if you don't have full A and B signal swings
the MPG inputs will not work either. There is something
wrong with your MPG dial if it does not output at least
TTL compatible signal levels (less than 0.8V for low and
greater than 2.4V for high)

... and I meassured again:

"normal position":
GND - S0: ca. 200mV
GND - S90: 4.06V

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

So S90 is 90° before/ after S0.

But then it should be a single ended encoder with S0=A and S90=B , isn't it ?
I don't know, what I meassured with my scope... maybe, I shouln't believe in its voltage-values
The above mentioned Voltages are meassured with an "normal" multimeter.