Assignment 8: Output Devices

   This week, I knew I wanted to do some motor control -- a necessary component of my future thoughts of making modular machines.    Steppers work open loop, and in the design stages of the week, I was looking at controller chips, creating Eagle footprints, and experimenting with laying out some boards.    Many devices are now in a HSSOP package, and it looks like boards should be rapid-prototypable.   

   Some things came up, and my implementation/debug/test time was short this week, so I scaled back to stuffing what should be the simplest board... an 8 channel MOSFET board using a bunch of IRF640's.     I then attached a unipolar (six wire stepper).

eagle fet board

   After layout and etch, I tacked some diodes on, since the loads would be inductive.    The interface was designed to work with my board from assignment 5.
fet board stuffed
   I had high hopes for USB and a couple of steppers without a controller.    Unfortunately, I would be short pins, and time.   Maybe next week?  

How to debug?

   What was cool, was that I could add a connector to the ribbon cable, and then plug in my blinkey light board also from the assignment 5 week.    This meant I could watch the bits twiddle as stuff ran!    Great fun, and a big help.    Here is the assembled layout.
everything fet


   Lights blink!   Motor Spins!   Torque sucks.    I suspect that I may not be driving the mosfets hard enough to turn them on for higher currents.     I should also double check my drive algorithm.    It will be a handy board, but it might need to go to a second rev.


   Compressing video:
         ffmpeg -i 11212011040.mp4 -ar 22050 -ab 32 -f flv -s 400x300 video.flv

   Is the A3977 and the DRV8811 pin for pin compatible?