Introduction: Sim900 for PC

About: Brison

Here is my first instructable's post. Hope you like it :)

In this project i want to show you how to connect Sim900 or other series of simcom's to the PC via TTL module. A simple but useful project!

Here are some pice of important you need to build the project:

1.Sim900/900A module,
which I've purchased it form :

2.DC-DC LM2590 - Adjustable
InputVoltage : 1.23v ~ 30v 3A

3.Power Jack

4.TTL to USB module

5.Plastic Box

6.Adaptor 5V 1.5 ~ 2A

7. MA - Antenna

8.Some LEDs

9.A push button

10.USB-F socket

11.USB to USB Cable

12. Some pieces of wire

Step 1:

Desolder pin headers from sim900's module.

Step 2: Cut Out the Antenna Socket

Since we're not going to plug in the antenna directly, you can cut out the Antenna socket. And flatten it pins.
Or also you can desolder it, and solder the SMA to its pads. (not a good idea :/ )

There are 5 pads for this component on the board. The centered one is the antenna pin and all the others are just grounded.

Step 3: TTL Module

You need to desolder the USB-M socket and replace it with USB-F.

Step 4: Connect TTL to Sim900

4 wires are connected to the TTL module. According to its labels we have:

Red: 5V
White: RXD
Green: TXD
Black: GND

Since we must use 3.2~4.4v for sim900, DO NOT solder the Red Wire to it.

Connect the white wire to sim900s TXD by a 200ohm resister to sim900's RXD (which in my module its pin number 10, its also the chip's 10th pin, check your own modules datasheet) and the green one directly to TXD (pin number 9).
Also you need to connect the black wire to the modules GND.

Step 5: Power Source

Connect input voltage of power module to the adaptor's power jack. And also it's output to the modules.

VBAT or VCC -> +
GND -> -

Adjust the output voltage by spinning the potentiometer to 4.2v.

Make sure you have at least on high-capacity capacitor in your power circuit. Use one 1000uF for your modules out put. I had one on the board.

Do not connect TTL's Vcc or the red wire to any point of your circuit. Just leave that pin open.

You can use any adapter to power on the circuit.(5v-12v-20v) Just make sure it gives at last 1.5A .

Step 6: Put All in Box!

Put all the boards and modules in the box.

Step 7: Drills

Drill 3 holes for LEDs and 1 for the Push Button. And connect LEDs to the module.

Step 8: Finalize!

Use a simcard and put all in the box and connect the adaptor to the jack.
Use the usb cable, for connecting it to the Computer.
Be sure you're TTL module's driver is installed on the computer. Connecting it, computer will recognize it as a Com Port (like COM11).

Download the EASY900 software from:

From settings, chose a comport, set the boudrate on 9600, and click on connect.

Push the button on the box and hold it for a while (1s). Wait for the yellow LED to blink slower. If every things goes right, you'll get some texts on the terminal. You can use all other futures of the application, calling a number, sending sms, saving contacts, receiving sms and so on.

Help us improve the application by letting us know the bugs and your useful ideas :)

Sorry for grammatical and dictation mistakes :P

Hope it helps ;)