Thing-o-Matic Extruder A3949 IC Relay fix

After burning out 2 A3949 motor driver ICs for the Plastruder feeder, I replaced it one more time and built a relay interface. My motor is over 20ohms, so I don’t understand why it keeps nuking the chip, but no more!

This took about 45 minutes to build on a perfboard, with an ATX power jack stolen from a CPU fan pass-through cable.

Direction relay only kicks in when there is a “reverse feed” called (which is rare). Better not to exercise a relay when the default off condition does over 98% of the work. The power relay energizes regardless what polarity the power is.