How I Burned My First STM32 (And What I Learned About Flyback Diodes)

Shortly after completing an Udemy crash course on baremetal programming, I decided it was time to finally take to the projects. Tired of just blinking LEDs and referring to microchip documents to figure out where the registers are located, I was ready to create something REAL.

Since I have much too many plants that I can care for, I figured I can create a self watering planter. By using an Air Purifier shell (which originally had a burnt fan), a 12V submersible water pump, and a STM32 Nucleo M0 development board; the base was set. The goal was to program the board to release water at set intervals biweekly so I do not have to. I was now feeling like a REAL embedded systems developer, or so I thought.

Let's flash forwards to the setup, I was utilizing a MOSFET with all wires placed properly. The microchip headers were fully designed and functioning with definitions from the Flash storage to GPIO initialization. The air purifier shell was adjusted to fit a water tank in the bottom along with all wires being routed upwards to a safe zone away from the water.

My only drawback was missing a “Flyback Diode” which would effectively prevent any sudden voltage from returning to the STM32 board, but I decided that the wait was too long and nothing would definitely go wrong. I only had one development board and began to connect all the wires.

Here comes the day of the disaster; my resistors were placed and I had connected my shared grounds. The GPIO Pin was set to output and was routed to the MOSFET Gate. I can hear buzzing coming from the motor as the circuit was powered on. The pump’s motor, being an inductive load. generated a voltage spike the moment the current was cut. With no flyback diode to absorb it, that spike had nowhere to go but back through the circuit into the STM32.

My attempts at trying to resolve this was ultimately a failure as a portion of the board gets hot to the touch. Overall if you are a beginner and are ready to work with voltage/power, please ensure that you have the proper equipment, such as a flyback diode, to ensure your board is safe.

Follow along as I try and complete this project, hopefully with a flyback diode and a new board on GitHub — and find me on LinkedIn and my portfolio.