I am using a SIM800L module with a Texas Instrument Launchpad, with a MSP430G2553 microcontroller, not using an external library for SIM800L.
Problem Statement: A Simple text message (SMS with Text Mode) is sent, received as a blank message on cellphone.
SIM details:
1. SIM 1 : Location: India. Operator: AirTel, 4G compatible SIM Card.
2. SIM 2 : Location: India. Operator: Tata Docomo, 3G compatible SIM card.
What I know already:
- UART Drivers in firmware are tested and working, non-polling, interrupt driven.
- No blocking time delays added as a substitute to read responses of AT commands. I read the response and proceed only if positive acknowledgement is received,
<CR><LF>OK<CR><LF>for most of the commands. - I have confirmed the data bits transmitted and received on Tx-Rx pins by means of an oscilloscope. Everything seems as expected, including voltage levels.
What I have read:
Some speculation through unofficial sources (Of course forums) that SIM800L is only 2G compatible.
(Shallow reading from wikipedia) I have read through GSM 3.38 and GSM 3.40, and the Data Coding Scheme section for understanding how the encoding of text is handled in suited/relevant AT command (AT+CSMP).
Various forums including the ones for arduino with which SIM800L modules are very popularly used.
Related posts on Stackoverflow:
- Recieving Blank SMS SIM800 using AT Commands and Python on Raspberry Pi 2
- How to send SMS with GSM module SIM800 and Arduino Uno?
- Sending GSM Character Set in SMS with SIM800L Module
The answer in the first one seemed to have worked for him, it didn't work for me.
What have I tried:
I have used the same module with an instance of Docklight serial terminal. SMS sent from Docklight are received on my cellphone and appear as expected, not blank.
On day 0, before integrating module with Launchpad hardware, I have tested the overall firmware state machine with exact copy of expected responses from SIM800L.
The results for both the SIM cards are same, except for some of the initial configurations, but I load a typical set of configuration in both of them before I initiate any SMS related task.
Typical values that I use are:
- Echo Off
- CSMP: 17, 167, 0, 0 (I have tried 17, 167, 0, 0, but no luck). Default from SIM 1 is 17,11,0,246, and that from SIM 2 is 17, 255, 0, 0.
- CSCS: "IRA"
Failed combinations on serial port: (SIM 1 and SIM 2)
- CSMP: 17, 11, 0, 246 | CSCS: "IRA" - Sends a blank SMS
- CSMP: 17, 11, 0, 246 | CSCS: "GSM" - Sends a blank SMS
- CSMP: 17, 11, 0, 246 | CSCS: "HEX" - Sends a blank SMS
Successful combinations on serial port: (SIM 1 and SIM 2)
- CSMP: 17, 167, 0, 0 | CSCS: "IRA"
- CSMP: 17, 167, 0, 8 | CSCS: "IRA"
- CSMP: 17, 11, 0, 0 | CSCS: "GSM"
- CSMP: 17, 167, 0, 0 | CSCS: "GSM"
- CSMP: 17, 167, 0, 8 | CSCS: "GSM"
To be honest, I played hunch with these combinations before I studied what field reflects what change these combinations (which are poorly documented in the SIM800L User guide).
Any idea what I might be missing here? I am open to thinking that it is more of a RTFM (Read The Fat Manual) issue.