SIM908-C GSM MOdule- No voltage on SIM VDD

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engr.waqas

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Hi
I'm using sim908-C and have designed the hardware as described in its hardware design document. My issue is i'm not getting any voltage on SIM VDD and sim908-C is unable to find network i.e. relevant LED blink rate does not decrease.
When I power up the module I see some mV on SIM VDD for very short time then it reduces to 0V.

Please suggest what should I do?

Just for your information !
-I'm powering sim908-C directly from a lead acid 4V battery which can provide 2A burst
-I have tried 100nF and also 200nF capacitor on sim vdd
-100 uF capacitor is placed on sim908-C vdd (very close) as recommend by its hardware design guide
- I have tried another SIM908-C but still no success

Regards
Waqas Shafique
 

Hi,
I also meet the same issue. I try with SIMCARD insert and not insert. But the voltage show on SIM_VDD pin still very low.
Now, I haven't solution yet.
pls, help me
Thank,
 

diepvu1805 said:
Hi,
I also meet the same issue. I try with SIMCARD insert and not insert. But the voltage show on SIM_VDD pin still very low.
Now, I haven't solution yet.
pls, help me
Thank,
Click to expand...

Whats the status of Netlight LED?
 

I connected a LED to Netlight pin. After power on SIM908, this LEDs was blink.
 

hi all,
I found the problem. The problem is VCHG pin. In my design, I used 2 power supply: Main and battery (Lion:3.7V),Main power's used to charge this battery. When power on SIM908 modem auto enter the charge mode, so SIM908 modem don't connect the network.
Now, I can connect the network.
But, I have meet new the problem. I can't charge for battery when SIM908 run in normal mode.
Can you suggest me a solution?
Thank all,
 
Reactions: Rod_O

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    Rod_O

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Hi,
Pls check whether the pin can meet the diagram? It seems the module can work now.
 

Really, i got the same problem.
I ll try your solution next week wen i restart my (almost dead) project.
Please tell me if you solved the problem about charging your batt.
Thanks a lot... XD (I really hope is the same problem i have)
Rod

- - - Updated - - -

Really, i got the same problem.
I ll try your solution next week wen i restart my (almost dead) project.
Please tell me if you solved the problem about charging your batt.
Thanks a lot... XD (I really hope is the same problem i have)
Rod
 

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