Background
This project started with a commercially available automatic wet pet feeder. The enclosure, bowl and mechanical opening mechanism were useful, but the original electronics were designed for scheduled feeding rather than dog training. I therefore removed the electronics and developed a custom controller based on an STM32 microcontroller.
The purpose of the project is to let a trainer reward a dog with wet food from a distance. Most remote dog-training feeders dispense dry treats or kibble, which limits their usefulness for dogs that prefer wet food or need a specific diet. With this design, the trainer carries a small 433 MHz transmitter and can open the feeder at the correct moment without approaching it.
Technical description
The 433 MHz receiver uses a simple ASK/OOK radio link. Its digital output is decoded by the STM32 by measuring the incoming pulse lengths with a hardware timer. The firmware reconstructs the transmitted frame and checks that it has been received repeatedly before accepting the command. This is important because inexpensive 433 MHz receivers can produce a considerable amount of noise when no valid transmitter is active. Frame validation and a lockout period also prevent a single button press from triggering the mechanism several times.
Once a valid command has been received, the STM32 controls the feeder’s existing actuator through the new circuit board. This makes it possible to reuse the original mechanical design while replacing the timer-based operation with direct remote control.
Radio reception also influenced the PCB design. The receiver requires a clean supply, local decoupling and some separation from the actuator drive circuitry, which can generate electrical noise when it switches. The antenna is kept away from large copper areas and other parts that could reduce its effective range.
From a firmware perspective, the feeder is implemented as a small state machine. It waits for a valid radio command, activates the opening mechanism for a controlled period and then returns to an idle state. Additional commands are ignored while an opening cycle is in progress, preventing unexpected actuator movement if the transmitter button is held down.
The result is a fairly simple embedded system, but it solves a problem that is not well covered by existing dog-training equipment. By combining the mechanical parts from an inexpensive wet-food feeder with a custom STM32 controller and 433 MHz radio link, the feeder can deliver a reward remotely at the exact moment it is needed.