Saturday, 6 August 2016

Old friends

So, I was trying to find a microcontroller board with a ton of 5V I/Os and, as usual, finding nothing at a reasonable price. A Pi Zero is $5, so why is a dev board for an 16MHz 8-bit MCU $50? But then I realised, I don't necessarily need 5V I/O - I need 5V tolerant I/O.

I've spent quite some time (as you might know if you've seen other blog posts) working with the TI Stellaris Launchpad - now known as the Tiva-C Launchpad for reasons I never did understand. I thought I've had a look at the datasheet and low and behold - 5V tolerant I/O.

So, a plan is forming:
  • Create a base board for the Launchpad, like I did for the in-car dashboard
  • Drive the L298 inputs from a open-drain GPIO with a pull-up.
  • Read the quadrature encoder inputs directly (the GPIO will deal with it OK).
  • It can interrupt on any GPIO pin, so no problem there.
  • It's fast - A 67MHz Cortex-M4F won't have any problems running four seperate PID loops.
  • The Pi can connect via USB for both power, control (Serial) and flashing/debug.
  • I know I can get the programmer to work.
  • I know I can program it in Rust...

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