4G SIM Module 4G LTE testing SIM7670C




1. Power- 3.7v battery and Circuit- Arduino boards or USB to TTL (CH340, CP210x)
Module TXD → USB-UART RX  
Module RXD → USB-UART TX  
Module GND → USB-UART GND  
Module VCC → External 3.8–4.2V supply 

  • Port: your adapter’s COM port
  • Baud: 115200, 8-N-1, No flow control
  • Line ending: try CR+LF, and also try No line ending
  • Type: AT then Enter (or send \r\n)


2. Commands
AT reply OK
AT+CGREG?
AT+CEREG?
    • +CEREG: 0,1 → Registered on LTE network.

    • +CEREG: 0,5 → Registered, roaming on LTE.
      If you see only +CGREG valid but not +CEREG, you’re on 2G/3G.

AT+CSQ

+CSQ: 18,99 >18 is Signal strength out of 31 so good 99 means No service
+CSQ: <rssi>,<ber>
OK
<rssi> = signal strength
 <ber> = bit error rate (ignore, usually 99)
 📡 RSSI value meaning (for LTE)
rssi Signal (dBm) Quality
0 –113 dBm or less Very poor / no signal
1 –111 dBm Poor
2–9 –109 to –91 dBm Weak
10–14 –89 to –81 dBm Fair
15–19 –79 to –71 dBm Good
20–30 –69 to –51 dBm Very good
31 –51 dBm or greater Excellent
99 Not detectable No service

 

 AT+CNMP=? 
+CNMP: (2,13,38)

Meaning
2 → Automatic (let the module choose)
13 → GSM only
38 → LTE only
So unlike SIM7600 (which has GSM + LTE hybrid modes like 51), your A7670C only supports these 3.
✅ What this means for you
If you want to force LTE only→AT+CNMP=38
AT+CEREG?
If it registers successfully → you are on LTE.
If it fails, it means your SIM or tower is falling back to 2G/3G.

 

If you want to force GSM only (fallback test) →AT+CNMP=13 

If you want to let module decide (default) →AT+CNMP=2 


 

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