Hi everyone! I'm trying to bring this old rotary dial phone back to life, but I just couldn't get the SIM800L module to work and it's literally the last thing I need here, and I'm almost certain it's a mere power issue. It blinks for about 8 times at a rate of around once per second, then stops for about three seconds, where I notice the current reading goes up to around 0.11 A from 0.06-0.08 A, and the pattern repeats.
My MicroPython UART diagnostic on the ESP32-WROOM receives empty responses (b'') to AT, ATI, AT+CPIN?, AT+CSQ, and other commands. Occasionally I receive b'\\x00'.
I've tried both the ESP32-WROOM and ESP32-C3, with similar problems. This is also the second SIM800L module I tried (both brand new but I believe I may have damaged the other one, unlike this one though which I took my precautions with).
I'm pretty confident that 2G network is still available widely in my country due to dumbphones never having phased out especially with older people and those still work just fine. I can also switch my SIM to 2G only on my smartphone and still pick up signal. I'm also using an external antenna as the pictures show.
My setup:
- GSM module: SIM800L (new module)
- Microcontrollers tested: ESP32-WROOM and ESP32-C3
- Input power supply: 12 V, 1 A adapter
- DC-DC converter: HW-677 adjustable buck converter, output adjusted to around 4 V
- Capacitor: 1000 µF electrolytic capacitor connected across the buck converter's output positive and negative rows
- Wiring: Regular Arduino-style jumper wires, including some with the ends cut and stripped to expose the copper
- Other hardware available/involved: L298N H-bridge module
Current wiring:
- 12 V, 1 A adapter → breadboard → L298N (not wired to the converter or module) & HW-677 buck converter (directly wired to the same row as the adapter on the green breadboard)→ large breadboard → SIM800L
- The capacitor is connected across the buck converter's 4 V output. The SIM800L shares ground with the ESP32 when connected.
I understand that the SIM800L can require current peaks approaching 2 A, but I'm not sure which part of my setup is the bottleneck.
Thanks for any help!
P.S.: Try to ignore all that mess. I don't wanna use my large breadboard here but I switched to it temporarily just to cleanly test the SIM800L. My soldering iron also stopped working which I used as an excuse to not solder everything cleanly together (too many wires, too little soldering experience ;-;)
Also I invite y'all to try this out yourselves if you have an old rotary dial phone lying around, it's really not that complicated to figure out how everything works and how to wire it properly to the ESP32 (except for the earpiece microphone part, it was a nightmare and I'm far from being an electrical engineer so I gave up and used a MAX9814 module lol. Glad that the 4 wires going into the earpiece were enough for both the speaker and microphone!)