Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] SIM900 Help - Garbage and ERROR response

Not open for further replies.


Newbie level 5
Nov 27, 2009
Reaction score
Trophy points
Spain CNY
Activity points
Hi to everyone!,

I'm also working with a SIM900 module...I turn it on via powerkey and it appear that is ok, but I get those errors:

1) If I put AT command it responds OK, also when for example I put ATE0 command. All appears to go OK!

2) I have configured the baudrate to 9600bps, so when I start the system and try to read the RDY indication I get that plus an ammount of garbage!...
I turn on the module using powerkey, and i get this frame:
Hexadecimal bytes: [0d 0a 52 44 59 0d 0a 0d 0a 2b 63 2b 0c 0c 63 57 3a 20 00 2c 30 0d 0a 0d 0a 4f 4b 0d 0a 05 c4 9f 9b 70 83 73 96 f3 b7 78 1d e8 5e 11 be 0e c9 cd 23 0d 0d 0a 4f 4b 0d 0a 4d 8f 54 b6 15 78 96 b1 e4 73 59 c2 50 49 4e 3a 20 4e 4f 54 20 49 4e 53 45 52 54 45 44 0d 0a 0d 0a 2b 43 46 55 4e 3a 20 31 0d 0a ]

Char bytes:

aW: ,0


+CFUN: 1

It's a lot of garbage!....anyone know the reason of that?...

3) Other command like AT+CPIN? returns directly "ERROR"

...the module responds the same whe I use the simcard and when i don't use it...
...I didn't view with the oscilloscope any voltage drop on vdd...I use 4.4 vdd voltage thought a BQ24070 from texas instruments...
...I view with the oscilloscope 64ms on and 800ms off signal...
... The module responds okto the commands A, AT adothers after the reception of the garbage....

Any idea?...Thanks a lot in advance

PS. I bought the module on ebay bid from China. i'm thinking that is an faulty SIM900 module!...

...thanks a lot in advance

did you put SIM card before powering ON the modem... seems to be power supply problem when it initialise at power ON.. what is the power supply you are using??the selection is hex format, change it to ascii format.. If you dont put sim at the begining of power ON you get CPIN error..........

Hi ckshivaram,

...first of all, thanks a lot for your soon reply!

...I have resolved the garbage problem!...It was a mistake with my reception buffer pointers, and the long response commnands got garbage...

Now when I power on, i get the following message!:


+CFUN: 1

I think that now is initializating ok!...

However it appears that the SIM900 can't access to the sim card...even if I put the card or don't it...
I have made the design that the HD recommends:
- On clk, data and reset I have put 22 ohm resistors.
- On data pin of SIM900 I have put 20pf capacitor.
- I have realised that I forgot the 100nF capacitor on VDD pin of the sim card.

Could be that the reason why the SIM900 don't identify any SIM card even if it is inserted?...

Thanks a lot in advance!...

The power suply I designed is based on BQ24070 Li-Ion Charguer, power suply from Texas Instruments. I get the same result using a 800maH battery or using a 5V 2A wall charguer.

In the theory, powering the system with a fully chargued mobile battery, and with a pcb with good vcc and gnd planes, and some tantalum and eletrolythic capacitors near the VBAT pins should start up ok!...



Hi ckshivaram,
- I have realised that I forgot the 100nF capacitor on VDD pin of the sim card.

Could be that the reason why the SIM900 don't identify any SIM card even if it is inserted?...
Yes, you need that capacitor for the internal regulator to function - you may find that operation is more reliable with a 220nF cap. Measure the voltage on the VDD pin with the SIM card inserted. If it is Zero volts the regulator is shut down.

Not open for further replies.

Part and Inventory Search

Welcome to