I'm working on phone-controlled car park gate. Trusted employees numbers are saved on SIM card/hard coded in program. So the idea is, if a trusted person calls the "gate number" ; Nodemcu will trigger a relay. The key issue is the "CLIP:" line which is supposed to appear each time on the serial connection during incoming call. When it appears I can parse it in order to determine if the "source" number is "trusted". CLIP: line is the only one where the "source number" is visible. I've got the impression that the line sometimes appears and sometimes not. There is no rule , but usually it appears right after rebooting the controller . So now, I'm rebooting my Nodemcu every 10 minutes but even that doesn't guarantee success. Furthermore, the "RING line" appears on the serial connection always during the incoming call (but in RING line there is no number) I've already tested 2 GSM modules, based on SIM800L & A6 GSM/GPRS chips. The same problem. I got stuck with and have no more ideas. Maybe someone here had the same problem? Thanks for any help.

PS of course I send AT+CLIP=1 to the GSM module in setup function, and later in the main loop (just in case)

--------------- the most important piece of code below ----------

void loop() {

  while(mySerial.available()) {
    incomingByte = mySerial.read();
    inputString += incomingByte;

  if (inputString.indexOf("MYNUMBER") > 0){
    trustedisCalling();//this function does the rest and it's OK

when I uncomment:


Sometimes I can see the CLIP line on serial console but sometimes not. RING notification, which is subsequent to CLIP appears always during incoming call.

  • Can you show us the sketch you're using?
    – VE7JRO
    Commented Oct 27, 2019 at 18:55
  • I put the most important part of code to the first post.
    – MarkusPL
    Commented Oct 27, 2019 at 19:57


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