SIM900A - am I being stupid?

Thread Starter

liamcrayden

Joined Dec 3, 2012
2
I'm making a project that involves interfacing with a SIM900A to send SMS messages.

I have purchased the following item:
http://www.ebay.co.uk/itm/SIM900A-5V-V4-0-Kit-Wireless-Extension-Module-GSM-GPRS-Board-Antenna-Tested-/331854225639?hash=item4d440da0e7:g:FnAAAOSwubRXNFiB

The seller is not technical, and is probably just a reseller or distributor - he couldn't answer my question.

To keep things simple, I've connected the SIM900A directly to the serial port of my PC (using on-board MAX232), but the actual project will be on an AVR. The SIM900A is provider locked to Asian countries, so I have flashed original SIM900 firmware (worldwide unlocked) to the board, which works fine. I can communicate with it no problem, all responses respond "OK", except the SIM card is never recognised. It's worth noting however that I had the same problem before I changed from the original SIM900A firmware, so this is unlikely the problem.

On power up I receive the following message in the console:

Code:
:+CPIN: NOT INSERTED
... which indicates that the SIM card is not detected (regardless of provider lock). I have the circuit powered by 5V 2A supply, more than adequate. I have been reading that the SIM card expects 3V3 to power up.

Pin 30 of the SIM900 (SIM_VDD) measures 0v. I have looked up the pinout of the SIM connections themselves and directly soldered 3V3 power to the SIM, but this doesn't seem to make a difference.

Am I being stupid? Should I be providing the 3V some other way? On the eBay listing it says:

  • Two power supply interface: VCC5, 5V DC above 1A. Computer 5V power supply can be early computer USB. DC long data circuit over larger recommended 5V1A. VCC4, 3.5--4.5V power supply, ibid., suitable for lithium battery.
But the board itself only seems to have VCC5. Please help! :(

Datasheets here:
http://www.amuroboclub.in/downloads/ebooks/GSM_MANUAL_SIM900_Hardware Design_V2.00.pdf
http://www.espruino.com/datasheets/SIM900_AT.pdf
 

Thread Starter

liamcrayden

Joined Dec 3, 2012
2
Worked it out. Three UK (Hutchison Telecom) is a 3G/4G only network, there is no 2G capability. As soon as I tried a Vodafone or O2/Telefonica SIM card it connected up straight away.

How annoying! Hope this helps somebody else.
 
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