▲ 3 r/IOT
GSM SIM800L EVB + ESP32S3mini can make calls but SMS sending hangs at AT+CMGS
Need help with SIM800L + ESP32-S3 SMS issue
The team i'm mentoring using:
- ESP32-S3 Mini
- GSM SIM800L EVB
- 3.7V / 7.4V battery setups tested
- common GND connected
- TX/RX connected correctly
- 1000uF capacitor tested also
Current status:
- AT commands work
- AT+CPIN? works
- AT+CSQ works
- AT+CREG? gives 0,1
- Calls work perfectly
- SIM card works normally in phone
- SMS center number exists (AT+CSCA? returns valid number)
Problem:
SMS sending is unreliable.
Earlier SMS worked 2–3 times successfully, but now AT+CMGS often hangs before getting the “>” prompt.
After increasing delays, now I sometimes get:
>
Prompt received
and the message text prints, but final +CMGS / OK response does not always come and SMS may not arrive.
Also sometimes ESP32 resets during SMS transmission with:
rst:0x7 (TG0WDT_SYS_RST)
Things already tried:
- longer delays
- separate power
- different baud rates
- capacitor across VCC/GND
- manual AT testing
- checking SMSC
- checking network registration
Could this still be a power issue during GSM burst current, or something carrier/SIM related?
Any suggestions appreciated.
u/Late_Curve1983 — 2 days ago