Fix ESP32-SIM800L AT Response

My ESP32 Dev Module refuses to return anything when I send AT commands to a SIM800L red board. The wiring follows the usual guides: GPIO27 to the SIM’s RX, GPIO26 to its TX, grounds tied together, the SIM powered directly from a single 18650 cell. I’ve triple-checked every jumper and even dropped a 1 kΩ resistor on GPIO27 and a 2200 µF capacitor across the SIM’s Vcc–GND rails—still silence.

I’m compiling the sketch for the standard “ESP32 Dev Module” target in the Arduino IDE and the board is on a direct USB cable to my laptop. Serial monitor shows the commands leaving but not a single character coming back.

If you know this pairing well, I’m looking for hands-on guidance that quickly pinpoints what I have overlooked—whether that’s level-shifting, power conditioning, firmware quirks or a cleaner software approach. A concise set of working code plus a corrected wiring/power diagram that reliably echoes “AT” with “OK” will be the proof it’s fixed. Remote debugging via chat or video is fine; I can test changes in real time and report scope/logic-analyser captures if needed.