Newbie needs help: quadrature and digital IO

Oct 25, 2003 3 Replies
E

Hi All,



I am working on a mobile robot project at home. I need to read two or three quadrature (single-ended) encoders for accurate angle measurementa in real-time (~100 Sample/s). Can one of national instruments PCMCIA card do this? I also need to output a PWM signal to a motor controller. Can both of the tasks be done on the digital IOs from a PCMCIA card? A laptop will do actual computation based on the measurements. How difficult is to lean to write these drivers? I have a fairly complex (~5000 lines) of c code for the computation and want to interface it with the measurement. Please help.



Thanks.



Everett


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R

Only if it is specifically designed to read quadrature encoder pulses. A general-purpose counter/time board usually does not have the needed circuitry to convert A and B phase pulses into up-counts and down-counts, although some do. Check with your supplier.

Not really. General-purpose digital IOs cannot be controlled with enough timing precision, especially under Windows, to do a good job at PWM. There are timer/counter boards that will do this, though.

-Robert Scott Ypsilanti, Michigan (Reply through newsgroups, not by direct e-mail, as automatic reply address is fake.)

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This low cost unit will work if you use absolute instead of quadrature encoders and feed into the A/D inputs (4). You then don't have the problem of powerup synchronization that quadrature encoders have until they pass the home position.

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