Encoder Output Problems

[Mike]

I have a Grayhill 63R128 encoder, an Atmel STK500 development board and a LeCroy 9354M oscilloscope. I have it hooked up like so:

Encoder Positive In -> 5vdc pin of Atmel Development Board
Encoder Ground -> Ground pin of dev. board
Probe 1 -> Encoder Output A
Probe 2 -> Encoder Output B
Probe 1 Gnd -> Board ground
Probe 2 Gnd -> Board ground

However, it's not returning a square wave back. Here's the o-scope screen dump http://img.photobucket.com/albums/v71/mikeperson/screendump.jpg

Thanks,
Mike

[sciguy125]

I'm not sure if I'm reading that scope printout properly, but I think you're on AC coupling. Also that waveform is what I'd expect from a square wave on AC coupling. Put it on DC coupling and see what happens.

[Mike]

I'm not sure if I'm reading that scope printout properly, but I think you're on AC coupling. Also that waveform is what I'd expect from a square wave on AC coupling. Put it on DC coupling and see what happens.
I just set the coupling to "DC50Ω" and it's still doing the same thing :(

EDIT: Same thing, but Output A isn't showing anything.

[Manoel]

If changing to DC coupling didn't help, you may have attenuated probes. Look for a small slider with 1X 10X 100X or something like that on the probe, and play around to see if you get a prettier signal.

[billbo911]

I just set the coupling to "DC50Ω" and it's still doing the same thing :(

EDIT: Same thing, but Output A isn't showing anything.
The wave form output you gave, (and by the way, that goes a long way in helping us understand what you are dealing with, good work! :D ) displays a classic waveform display of a square wave read through an AC coupled channel. I am not familiar with that particular scope, so when you say you set it to "DC50Ω", I am not completely sure what that means for your scope. I can only assume that it is not correctly "DC" coupling probes 1 and 2 which, according to the picture, are connected to channels 2 and 3 respectively. The part I don't follow is the "50Ω" after the "DC". That is not a setting that I am familiar with for any scope. Also, as Manoel stated, for correct calibration purposes, make sure the probes are set to the same attenuation value that the scope is looking for. Some scopes do this automatically, some do not, so just double check it.

If possible, can you put up another picture of what your screen looks like with the new "DC50Ω" setting?

[Mike]

I emailed my electronics mentor and he said that I may need a pull-up resistor. I've never used an oscilloscope before, my dad bought this (industry grade) one home from his work, so it's really complicated...

I also posted on another forum, and they said DC50 is wrong

that requires substantial DC drive. Basically in 50Ω mode the scope places a 50Ω resistor to across the probes tip and gnd.


I put it in DCM1Ω and I am now getting back correct square waves.

Thanks for the help =)