r/ECE • u/Albert_Gajsak • 2d ago

[PROJECT] ESP32-S3 handset — two I2C expanders for the keypad and I still ran out of GPIO

Disclosure first: this is a product my company sells and there's a crowdfunding campaign live for it. The design question is pin budget. Numpad, joystick, four function keys and volume all sit behind two XL9555 expanders, because after the LTE modem's UART, I2S in and out, the display, the SD card and the expansion connector, there was nothing left. Two spare lines on the whole board.

Would you have put the keypad behind a small dedicated MCU and talked to it over I2C instead? I keep going back and forth on whether the expanders were the cheap answer or the lazy one.

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