18v7 Powers on with only GND and RESET pin connected

So I have what I believe to be is a weird problem… With just the reset pin connected to 5v and the gnd connection made (on the logic side of the board), the motor controller powers on. Is this normal?

There is no other voltage present in the circuit… No connections are made to Vin and ground on the motor side, and no connection is made to Vin on the logic side. I think it may be due to the fact that I possibly fried the board. I accidentally connected a 12v dc power supply to the motor end and connected, on the logic side, Vin and gnd to an ardunio’s respective Vdd and gnd ports which in turn, fried the ardunio…



In general, it’s possible to partially power unpowered microcontrollers through their I/O lines. The internal structure of an I/O pin typically includes diodes that keep the pin voltage within the allowed range by clamping voltages above VCC to VCC and voltages below zero to ground. This means that current can flow from the pin to VCC if the pin voltage is higher than VCC, which in turn can power the MCU. Note that this is not a reliable or recommended way to power the board!

This is probably what you’re seeing on your Simple Motor Controller 18v7. It should be somewhat easy to tell if you fried the board: does it still function if you connect power properly? From what you described, the main potential for damage to the motor controller would be to the trace carrying VIN to the logic side of the board, and this connection is not crucial for operation.

- Ben