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Sim900 auto-Power down after network registration

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tlogic

tlogic

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Hello i have developed a board which sends data over gsm using a PIC and SIM900 gsm module. When i power it up with sim card plugged in, the SIM900 status led starts blinking 64/800ms and after a few seconds it stops blinking. What i get at the uart are the following


----------------- SIM INSERTED -----------------
RDY

+CFUN: 1

+CPIN: READY

+CREG: 0

+CREG: 2

Call Ready

+CREG: 1,"001F","1174"

then powers off with no msg

----------------- No SIM -----------------

RDY

+CPIN: NOT INSERTED

+CFUN: 1

+CREG: 2

+CREG: 0

then stays on
 

You may have some problems with the power supply. Make sure that it can provide 2 Amps necessary for transmission bursts (network registration, gprs transmit, etc). See chapter "3.3 Power Supply" in the Hardware Design documentation. A quick and dirty fix is to use a very large capacitor (1000uF-2200uF) on the power supply to see if it solves the problem.
 

Well i don't think that is the power supply i power it with lab power supply DC 4volt 3Amper i also tried to connect a 3300uF capacitor as you said above but the problem still exists
 

have you checked the voltage on the STATUS pin? does it become LOW with the sim card connected?
how about the POWERKEY pin? btw, after network registration the status led should blink 64/3000ms (NETLIGHT pin).
 

zoranx said:
have you checked the voltage on the STATUS pin? does it become LOW with the sim card connected?
how about the POWERKEY pin? btw, after network registration the status led should blink 64/3000ms (NETLIGHT pin).
Click to expand...

Power supply: 4Volt 3Amper DC
(Also tried to connect a 3300uF capacitor parallel to the power supply with no result)

Well the status pin is 0Volt when the module is off. When it is powered on it goes about 2.9volt after the NETLIGHT starts blinking. Then it goes to 0Volt again when the NETLIGHT stops blinking and turns off.

Until it registers to the network it powers off so it doesn't have time to change blinking to 64/3000ms.
 

The memorycapacity is 32k
 
could you try with a higher voltage? 4.1V 4.2V .. ?
 

Yes i tried with no result
 

please try this..... when it comes up.. just do a AT&F.... and try again.........

also check if the SIM pins have any short circuit which forces modem to sleep mode......
 

No result egain...

Uart output
RDY

+CFUN: 1

+CPIN: READY

Call Ready
Click to expand...
After it outputs call ready it shutdown and the led stops blinking.

I also measured the SIM_VDD pin and it is 2.8~2.9 Volt as it supposed to be.
Also without a sim card plugged in it doesn't power down.
 

Well before i designed the board i made the circuit on breadboard with sim300D and all worked fine. Then i designed it to PCB as it was on the breadboard and i sent it for manufacturing. When i received the PCBs i soldered two of them (with sim900D) and both of them have the same problem as i described above.

---------- Post added at 18:02 ---------- Previous post was at 17:57 ----------

I have also checked the sim card holder pins for short-circuit but everything is ok.
 

Here is the Scheme of the PCB.
TX RX and DTR normally goes to PIC16f877A. To testing i have removed the PIC and i have connected RX TX to PC rs-232(converter) and DTR floating.

**broken link removed**
 

you don't need R12, there is already a 15k pull-up resistor in the module.
i'm using a similar interface between sim and pic, but without C5,C6,C7.
could you try removing them and see if the problem is still there?
 

Well i replaced c7 with a smaller one about 1nF and i increased the supply voltage from 4.1 volt to 4.3 and it seem it works now.
At what voltage are you running it?
If i drop the voltage under 4.2 and i try to power it on it stops after "call ready" message sent.
If it is powered on and locked at a network and then i drop the voltage under 4 volt it stays on.
 
i still suspect a power supply issue. could you check the voltage drop at the power supply with an oscilloscope
and see what happens when the module turns off after "call ready"? i'm using 4.0V.

just another idea: could you use a Lithium-Ion/Polymer battery instead of the power supply? something from a
mobile phone for example. make sure it's not empty ;) this would definitely tell us if the problem is with the power supply.
 

Well i connected an oscilloscope i gave 4.2 Volt DC from power supply. When the module powers on voltage drops to 4Volt and after call ready it goes again to 4.2 (module powers off).
I also tried 4.4volt. When it powers up again voltage drops about 200mv from 4.4 to 4.2 and after call ready i can see on the oscilloscope some noise (mV picks) about a second and then noise stops (module works fine with voltage more than 4.2V).

I'll give it a try if i find a li-on charged battery.
 

do you have the gprs antenna connected? can you try with and without antenna, and see the voltage drop?
 

Yes i have it connected.

Well i tried without the antenna at 4Volt and it staid powered on after call ready.
With the antenna it stops after call ready msg.

???
 

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