SIM900A mini breakout board

Veröffentlicht von philipp am

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  • Working frequency: 900MHz / 1800MHz
  • Working voltage: 4.4 ~ 5.3VDC
  • Working Current: maximum of 2A, an average of 50mA
  • Sleep Current: 4mA
  • Communication Interface: TTL serial port
  • Baud rate: It can be set to be auto-bauding and it can also be set by AT command
  • Interface logic voltage: 3.3V
  • Make and answer phone calls using a headset or an external 8Ω speaker and electret microphone
  • Send and receive SMS messages
  • Send and receive GPRS data (TCP/IP, HTTP, etc.)
  • This is mini GSM / GPRS core board based on SIM900A. It supports dual-band GSM/GPRS network, available for GPRS and SMS message data remote transmission.
  • The board features compact size and low current consumption. With power saving technique, the current consumption is as low as 4mA in sleep mode.
  • It communicates with microcontroller via UART port, supports command including GSM 07.07, GSM 07.05 and SIMCOM enhanced AT Commands.

All documents regarding SIM900/SIM900A on the manufacturer’s website


Flashtool got from here

Firmware upgrade instructions

First of all connect module to VCC, GND, RX and TX and check if communication is possible by sending: „AT\r\n“

If it is possible you receive:



Next check firmware version by sending: „AT+CGMR“

I received:





Now go to, search for SIM900A and check for a newer firmware. If there is no newer firmware I recommend downloading and flashing one anyway, as you never know where the modules has been before and who flashed which firmware…

So I downloaded a firmware for Europe (Version: 1137B03SIM900M64_ST_ENHANCE) and the Simcom – sim900 Custom flash loader V1.01 and extracted both files. This firmware is actually a version for the SIM900 module, not the SIM900A. As I read here and here, SIM900A is made for the Asian market, not the European. So to use SIM900A in Europe, a SIM900 firmware can be flashed. The only important part is the megabyte-number in the firmware name shown here:


There exist 64MB and 32MB versions. So when you read out your firmware version above, note the MB-version you have and flash the according new firmware file.

Start up the flash loader, browse to the firmware folder and select the *.cla file, select the right COM port and hit the START button. Turn the module on and wait about 4 minutes until the firmware flash process is complete. If the firmware flashing was successful the flash loader window looks like this:

Afterwards reboot the module.


If your module is stuck in a reboot loop after flashing (because the module connects to the network):

  • make sure you have a power supply that can handle the required current
  • use short power lines (not too thin)
  • add low-ESR capacitors on your power lines directly on the module
  • maybe turn up the voltage by a few hundred millivolts (ONLY if voltage is in spec!! Never go above absolute maximum ratings!)


New SIM card:

  • Insert new SIM card into phone
  • Enter SIM pin
  • Wait until your phone says the SIM card is now activated
  • Disable SIM pin in options of phone
  • Done

Server side:

  • Don’t forget to add port forwarding to router
  • add new proxy to nginx
  • add port to iptables: iptables –list-rules to show all and then iptables -A TCP -p tcp -m tcp –dport 86 -j ACCEPT
  • to save the temporarily added iptables rule edit /etc/iptables/rules.v4

Kategorien: Allgemein

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