Module SIM800L is simple GSM modem, which could be connected via serial line (even SW serial). It could send/receive SMS and calls. The calls require connected microphone and speaker. SMS sending works fine without additional HW. A nice article (in Czech) is here. The modem needs good quality power input at 4.2V and peak current is 3A.
After power is applied the modem LED is blinking quickly about 10 times. Then it will be off for a while (modem is connecting to GSM network) and after successful connection the speed of LED blinking is slower. SIM should be inserted with contacts pointing to printed board.
The modem worked fine if there was good power input. The only problem was with time synchronization to operator’s time. Each sync has ended up with following time:
04/01/01,00:01:55+32
Any parameter change did not help. After some failures I have tried to change CBAND (Get and Set Mobile Operation Band ) parameter. The original setting was:
+CBAND: EGSM_MODE,ALL_BAND
The modem reported following options for CBAND parameter:
+CBAND: (EGSM_MODE,DCS_MODE,GSM850_MODE,PCS_MODE,EGSM_DCS_MODE, GSM850_PCS_MODE,EGSM_PCS_MODE,ALL_BAND)
I have tried “DCS_MODE” and it did not work, but the second try “EGSM_MODE” or “ALL_BAND” worked fine.
Change to EGSM_MODE:
at+cband=EGSM_MODE
OK
*PSUTTZ: 2018,10,31,17,15,19,”+4″,0
DST: 0
+CIEV: 10,”23002″,”CEZ”,”CEZ”, 0, 0
Change check:
at+cband?
+CBAND: EGSM_MODE
OK
and operator time is?
at+cclk?
+CCLK: “18/10/31,18:15:32+04”
After storing new settings into modem config (AT&W) the modem picks up the operator time immediately after power connection and connecting to GSM network.