Is it possible to use SPI on Redbot Mainboard?

Question

My students use the Sparkfun RedBot Inventor's Kit for their final design projects. The documentation about this board isn't great. There are connectors to SPI pins (they are not soldered to headers, but they exist, see diagram below); however the bumpers and wheel encoders use pins 10 and 11, which are pins used in SPI communication.

My question is: is it possible to solder headers into that SPI socket and use SPI communication without interfering with the bumpers and wheel encoders (for example if my students want to hook up a 7-segment display to show the RedBot's speed)?

Redbot mainboard

Answer 1

From the silkscreen on the board you appear to be either mistaken or already re-purposing signals - pins 10 and 11 are labeled as used for Servo position command PWM, not for sensor input.

Therefore, as long as you don't use those signals for servos (or ignore the labeling and use them for something else) there should be no issue using pins 11, 12, and 13 in the ordinary manner for SPI, by finding them in any available place on the board, including the 6-pin ISP connector your identify.

If you did need to use pins 11 and 12 for another purpose you could still "bit-bang" "software SPI" on any other available set of four pins.

It is also vaguely possible that you could share functions by connecting bumper switches through resistors - when the software is driving those signals as SPI outputs, it will dominate the resistors, but at other times it can re-purpose the pins as inputs to read the bumper switch state. However this may require modification of Arduino library code to accomplish repeated mode switching.

• lemontwist: The silkscreen doesn't correspond with how the Redbot is actually used. They are not used for servos, but sensors. The motors are DC motors and are driven by the ICs on the bottom of the mainboard. Thanks for the suggestions though!
• Chris Stratton: You can still use software SPI on any other available pins.