GSM Phone Prototype

A phone assembled from parts: an ESP32 driving a SIM800L GSM module, a 2.8 inch touchscreen, a speaker, a microphone and a battery, wired on a breadboard until it could place a real call on a live SIM.

A phone is four systems that all have to work at once: radio, display, audio and power. I wanted to see whether I could get them working together well enough to make an actual call, not just power on.

An ESP32 drives the SIM800L, which handles the cellular connection and takes a live SIM. The keypad is drawn on the touchscreen, so there are no physical buttons.

The test was simple: dial a number and see whether the other phone rings. It did.

Signal was the weak point. The SIM800L had no antenna fitted and I did not have one to add, so the module worked with whatever reception it could get on its own. It connected and made the call, but reception was the limit of the build rather than the wiring or the code.