Reading an encoder with a USB 6008

[e-Cash-Money]

Hello DAQmx users,

I have a USB 6008 and it doesn't work the way I want it to.  I have done no troubleshooting or research and I refuse to give you any more information.  You have 30 seconds to answer my question.   i kid, i kid...

So here is my real question:

I have a USB 6008 that we use to do simple analog output.  I'm looking for a way to use the USB 6008 to also get encoder information.  I know that the USB 6008 cannot read an encoder directly, but I was wondering if anyone knew of or had any ideas of external hardware that could be used inbetween the 6008 and the encoder.  I think it would be something like 1) the encoder generates pulses 2) external hardware takes encoder pulses, translates them into a digital value representing the angle and outputs this digital value 3) use the digital lines on the 6008 to read in the digital angle value from the external hardware 4) I don't lose my job.

I realize that this isn't an easy, optimal, or preferred solution, but I want to look into it before being forced to replace the USB 6008 with another piece of hardware.

(I accidentally posted this in the Motion Control forums)

[prithvi]

Hi,

You can use a "schmitt trigger circuit" as the hardware that sits between your encoder and your USB 6008. The schmitt trigger can give output 5 or 0 Volts as required by the DAQ.

[e-Cash-Money]

Hey prithvi,

Thanks for the info, but I've got some questions about the schmitt trigger :womanvery-happy:

It looks like a schmitt trigger is used to condition the signal (provide thresholds to filter out the noise) as well as bring the voltage into an acceptable range (0 to 5V for the DAQ).  However, it seems like I will still need some circuitry (something with counters in it, I'm guessing) that will convert  the encoder pulses into an angle.  I want to be able to sample N digital lines with the 6008 to get a digital value that represents the current angle.  I don't think that I will be able to read the encoder waveform directly with the 6008.

Perhaps I'm misunderstanding how I'm supposed to be using the schmitt trigger?

[Chris_Megdanoff]

Two approaches come to mind.

1) Without any custom circuitry, you can use a panel meter to count encoder pulses and convert to an analog output.  Daytronic has one that we just used on a project.  It worked well and allowed us to scale the output to the expected workable range of the encoder.  It directly takes in quadrature encoders.  Either differential or single ended types are supported.

2) You can use some counter chips, schmidt trigger, and other circuitry to put together a device of your own.  If you are under a time crunch, I would be careful doing this unless you are already experienced putting circuitry together.

Good Luck

[Ryan_V[DE]]

Eric,

Is there a reason that you can't use the counter on your 6008? Do you need absolute position? Will you be rotating in both directions? Have you already selected your encoder? Absolute rotary encoders have multiple tracks and detectors, providing digital outputs representing the absolute position of the encoder. This sounds exactly like what you want. There are also devices which convert quadrature signals to binary, such as this device.

DE for life,
Ryan

[e-Cash-Money]

Hello Chris ,

Thanks for the tips!  I was look into qudrature decoder chips but your reccomendations seem like a more viable solutions for us.

Ryan,
I'm pretty sure the counter on the 6008 only supports simple event counting (too lazy to check the specs right now ).  We will be rotating in both directions and I think I need absolute position (which I'm guessing is knowing the exact angle as opposed to relative position which just tells you which direction you are moving???)  We already have an encoder that we ripped out of something else, but I'm assuming that I can just get a different encoder if we need one.
Thanks for the link, it's exactly along the lines of what I'm looking for.

Hope things are going well in, what are the kids calling it nowadays, the "A-T-X"?

Message Edited by e-Cash-Money on 03-22-2006 12:56 PM

[Ryan_V[DE]]

Yo Eric,

600x only supports simple event counting on PFI0... didn't know if you needed direction. Let us know if you need anything else - you have my email. And as always, the "A-T-X" is superb.

Peace,