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Digital calipers

Digital calipers have an SPI like data signal that reports the current position. It's pretty easy to tap, with the caveat that the voltages are too low to trigger a +5V Teensy. Instead I enabled pull-ups on the data lines, which seem to back drive the MCU in the calipers and it seems to work without a battery installed.

On the scope Blue is the falling edge clock, yellow is 24-bits of MSB, twos-complement measurement data at 200 counts/mm. There appear to be spurious data transitions when the clock is high; it might mean something.

This could easily be cleaned up and turned into a nice Bluetooth or wired USB device.

USB Devices Hacks Teensy 2012

Last update: November 8, 2020