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General Tech Bugs & Fixes 2 years ago
Posted on 16 Aug 2022, this text provides information on Bugs & Fixes related to General Tech. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.
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I am using a SIMCOM SIM900 GSM/GPRS module in an embedded hardware application. Rather than sending device data to a server by SMS (what I've been doing so far) I want to switch and start using GPRS to post data to a server with a PHP script I've written.
The SIM900 literature (pdf) is abysmal. Section 13 gives an example sequence for connecting GPRS, which I've pieced together with a few other bits, but I can't get it working:
*COMMAND* *RESPONSE* *COMMENT* ATD*99# CONNECT Establish connection AT+CGATT? +CGATT:1 Check connection AT+CGDCONT=1,"IP" OK Set context AT+HTTPINIT OK Enable HTTP mode AT+HTTPPARA="URL","www.google.com" OK Set the address AT+HTTPDATA="data" OK Send some data
I am getting the expected responses, but nothing happens after the last step.
After much googling and mashing together various answers, I got it working.
Here's the AT command sequence. You can test this from start to finish, you'll just need to confirm the APN of the carrier you're using.
// My comments are here Command to send is here Expected responses are here // See if the SIM900 is ready AT OK // SIM card inserted and unlocked? AT+CPIN? +CPIN: READY OK // Is the SIM card registered? AT+CREG? +CREG: 0,1 OK // Is GPRS attached? AT+CGATT? +CGATT: 1 OK // Check signal strength - should be 9 or higher AT+CSQ +CSQ: 14,0 OK // Set connection type to GPRS AT+SAPBR=3,1,"Contype","GPRS" OK // Set the APN - this will depend on your network/service provider AT+SAPBR=3,1,"APN","wholesale" OK // Enable GPRS - this will take a moment or two AT+SAPBR=1,1 OK // Check to see if connection is correct and get your IP address // (I hid mine here, but you'll get a real IP back) AT+SAPBR=2,1 +SAPBR: 1,3,"0.0.0.0" OK // Enable HTTP mode AT+HTTPINIT OK // Set HTTP profile identifier AT+HTTPPARA="CID",1 OK // Put in the URL of the PHP webpage where you will post - // the URL below is a test server so you can use it in testing AT+HTTPPARA="URL","http://posttestserver.com/post.php" OK // Tell the SIM900 how much data you'll send (18 bytes here) // and how long to wait for a time-out (10,000 ms here) AT+HTTPDATA=18,10000 DOWNLOAD // Key in the data you want to send after you get the "DOWNLOAD" prompt. vdc=12&adc=3&rel=8 OK // Post the data - wait a second for the response AT+HTTPACTION=1 OK +HTTPACTION:1,200,142 // Read the response - www.posttestserver.com will give you a // URL where you can confirm that it's working AT+HTTPREAD +HTTPREAD:142 "Successfully dumped 0 post variables. View it at http://www.posttestserver.com/data/2016/04/28/14.19.041655610622 Post body was 18 chars long." OK // Close the HTTP connection AT+HTTPTERM OK // Disconnect the GPRS AT+SAPBR=0,1 OK
Edit to add: Here are the sources I used to put all of this together, along with help from some folks I asked in my lab.
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