Sunday, March 1, 2015

Velleman KSR6 kit, error in silkscren

Last post I talked about the KSR6 Velleman kit and that the robot didn't turn when closing in on objects. After troubleshooting the robot for a while, I finally found the error. The voltage divided node at U4 +in and U3 -in lay at nearly 6 volts, instead of the expected 3 volts (which in retrospect is odd, this voltage should instead be closer to 2V, only explanation I can come up with is that that R8 had a bad connection, but who knows?). This made the integrator U3 integrate only voltages over the node, which was almost nothing... After inspecting the schematics and the layout, it was obvious that the silkscreen component markings had mixed up R8 and R10. Switching them made the robot work the expected way.
This might not be true for all PCB versions. This PCB was marked 21-885. If you are uncertain, measure the voltage of pin 3 or 13 of IC1. It should be  close to 3V. If resistors are placed wrong, voltage will be closer to 6V.

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