SIM800L & Arduino UNO

I have the SIM800L module connected the Arduino UNO. I have the SIM800L supplied with 5 volts separated from the Arduino, from a power source. The power source is reading at 83%, which is more than enough power.

---> AT+CBC
<--- +CBC: 0,83,4065

VBat = 4065 mV
<— +CBC: 0,83,4065
VPct = 83%

The SIM800L is blinking at about 2 blinks a second.
I have the Hologram SIM card inserted the right way and I can detect it as well as read a message.

---> AT+CMGF=1
<--- OK
---> AT+CPMS?
<--- +CPMS: "SM",1,10,"SM",1,10,"SM",1,10

Reading SMS #1
—> AT+CMGF=1
<— OK
—> AT+CSDH=1
<— OK
+CMGR: “REC READ”,"+447937XXXXXX","",“18/05/24,14:16:47+04”,145,4,0,0,"+447797XXXXXX",145,1
***** SMS #1 (1) bytes *****

However, I keep getting this message when I try to send an SMS:


SMS Ready
Send to #+353894179097
Type out one-line message (140 char): hello world
—> AT+CMGF=1
<— OK
—> AT+CMGS="+353894XXXXXX"
<— >

hello world

The module keeps telling me: not registered, but I’m not sure how.

---> AT+CREG?
<--- +CREG: 0,0

Network status 0: Not registered

I’m Using the Fona test example from the Fona library, for simplicity and testing reasons.

I’ll appreciate any help on this? Has anyone ever come across this, and what worked for you?

1 Like

Similar problem.

Unable to resolve it either :frowning:

I would try to resolve the registration issue first, if you aren’t registered, you wont be able to reliably send and receive data.

If you are registered the light should blink once every ~3s. (every 800ms means not registered, every 300ms = connected to GPRS and tx/rx data).

Did you set the apn correctly? For reference the series of AT commands I used to initialize the SIM800H/SIM800L are:

"ATE 0\r\n" //disable echo
"AT+IPR=115200\r\n" //hardcode serial baud rate
"AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"\r\n" //use GPRS for IP based bearer
"AT+SAPBR=3,1,\"APN\",\"hologram\"\r\n" //set APN for IP based bearer
"AT+CSTT=\"hologram\",\"\",\"\"\r\n" //may also want to run this to set APN
"AT+CFUN=1\r\n" //set modem to full functionality

//then periodically run:
"AT+CREG?\r\n" //check if registered
"AT+CSQ\r\n" //check signal quality  first number in response should be > 5 for "ok" signal

This may not fix the SMS but is all I can offer as I don’t send SMS from my device but you definitely need to fix the registration problem before tackling SMS.

Also make sure you have the antenna properly connected and use a decent antenna, the tiny ones that come with most SIM800L kits are complete crap. I’d spend like 10-15 bucks on a GSM dipole antenna from amazon or ebay, don’t get one with an integral long RF cable, these RF cables are also crap and the cable loss will attenuate too much signal. Or, if you re ok with shipping being more than the part itself, I use a Laird EPR8221A1-15UFL and have good results.

1 Like

@AndrewGifft – thanks very much for the guidance. I’ll try it tonight.

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