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I'm not sure whether this questions fits here or at electrical engineering stack exchange. Nevertheless...

I have an SIM800L modem controlled through serial port. Inserted SIM belongs to an O2 Czech Republic operator (230 02). When I make a call from the device to my phone and then I reject it, the modem does not detect it. It just thinks that the other side still rings. It takes ca. 20s after the hang-up when the modem terminates the call. And that's a problem for my implementation. I need to know this (almost) immediately.

I tried everyting from the SMI800 commands docs. Namely:

  • CDRIND=0 (+CDRIND arrives after ca. 20s after hanging)
  • ATX4 (Or ATX(0..4) does not shorten the interval)
  • ATS7 does not have any effect
  • ATS10 does not have any effect
  • COLP? returns 0,2. After setting COLP=1, the lag is the same and the result is BUSY (or NO CARRIER, depending on ATX, of course)
  • MORING=1 (does nothing worth mentioning)

Do you have any idea?

rudolfdobias
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  • Unfortunately it might depend on your operator. Do you have an alternative SIM to perform a simple test? – Roberto Caboni Feb 19 '21 at 08:04
  • Do you get a different behavior using `+CLCC` like I explained in [this answer](https://stackoverflow.com/a/63267569/11336762) some time ago? – Roberto Caboni Feb 19 '21 at 09:01
  • @RobertoCaboni I'm going to test another operator soon, so no info yet. +CLCC reply is unfortunately unaffected after rejection. I realized (because I don't hear it) that other side does not hang up but the operator plays an audio "We're sorry, but the target number..blah blah". So maybe the question is if there are any tools for ringtone detection? – rudolfdobias Feb 19 '21 at 13:25
  • Well, if the remote device doesn't hang up the behavior you described is correct. – Roberto Caboni Feb 19 '21 at 13:56
  • I see. But there should be some way to achive this, or shouldn't? – rudolfdobias Feb 19 '21 at 18:40
  • You say detecting that on the other side there's a recorded voice? Not with AT commands. All you can do is maybe detecting the busy signal (but I'm not sure about the command to be sent on SIM800) – Roberto Caboni Feb 19 '21 at 19:11

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