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PWMPAL and QTI sensors — Parallax Forums

PWMPAL and QTI sensors

JED1JED1 Posts: 17
edited 2006-04-10 19:55 in Robotics
I just wanted to share an item I just learned about the PWMPAL and the QTI sensors.· I recently built a MiniSumo robot using a stamp II and the PWMPAL so I could use a DC motor to provide higher torque.· I had the PWMPAL drive the motors with an H-bridge.· The PWMPAL uses pin 0, and can use 8-15.· I didn't need to use the functionality of the pin 8 - pin 11, in which the application sheet tells you can then use as normal I/O prints from the stamp.· While this is true, I found a combination to watch out for.· I was also using the QTI's as my Tawara line sensors.· They are used in the RC time method.· I had one sensors I/O pin in the pin 1 - 7 range and the other one in the 8-11 pin range.· The two sensors always came back with vary different responses to the same input.· This presented a problem when trying to use a common (averaged) threshold for both. I wondered if the PWMPAL wasn't affecting the RC circuit for the one sensor, so I re-wired all the I/O and made sure that both QTI's were in the pin 1 to 7 range.· Now they both work and respond with comparable outputs.· Bottom line is that the PWMPAL does affect the impedance on those shared pins so be for warned and hopefully you won't have to spend all that time I spent troubleshooting.·

Hopes this help someone save some valuable time.
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