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sim900 not providing SIMVdd

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Full Member level 5
Sep 24, 2010
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hi i have a problem with my sim900 module it is not providing SIMVdd, its accept all at commands but gives error on at+cmgs=" phone number". it response is +cms: error 310 which mean that sim not inserted. even though i have inserted sim to sim jacket.
kindly help me out
thanx me in advance

check whether the GSM is configured properly or not..........

i,e it requires around 2amp current initially to get configured.....

if it not configured then why its giving response of all commands except at+cmgs and its properly powered with supply

hi plz check this attachment for sim connection sim900.JPG

You need to add a capacitor to the SIM_VDD line (pin 30) - the voltage regulator in the SIM900 needs a capacitive load to function. I've found that a .22uF works best.

GSM_MAN i have added 100nf capacitor, u may see on schematics

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GSM_MAN i have added 100nf capacitor, u may see on schematics

Your schematic is small and fuzzy and hard to read. Do you have 2 SIM sockets? I've found that a 100nF cap is not always sufficient, try a .22uF instead.

Sorry, but your schematic is too fuzzy, and I'm not really sure how you have everything connected.

hi ,
connect sim presence pin directly to ground and you will surely get vdd supply around 2.8Volt on simvdd pin.

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Sorry, but your schematic is too fuzzy, and I'm not really sure how you have everything connected.

Hi I am new to electronics.
I am not getting voltage on sim_vdd.

Could you please help me with that.

Could you please share you schematic with us.Or can you please mail the schematic to

Thanks in advance.

Attaching the my schematic.


  • Gray_logix_sim900.png
    75.6 KB · Views: 67

set your digital multimeter on diode check mode & connect Red probe to sim holders GND(pin5)
touch black probe to other pins of simcard holder one by one it will have to show
reading 700 to 900 on meter
if reading is 0 or reading >1000 there is mistake in sim holders connection

also check shorting for simcard holders pins on module side

sim900A shows same reading with Modules other pins expect Gnd,Power,Ant.with this method
Use R1,R2,R3 100 Ohms R4 4K7,C1 100n.

Use 10to15 turn3-4mm spacing wire wound on pencil(remove pencil after winding) for antenna. antenna must have to connected &erected vertically

I have to see your PCB footprint for more Details
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I know that no one may ever see this but this message is meant to be a message of hope. I was having this same problem but never could figure out what was wrong. I checked the connections of my sim card 20+ times. I "knew" everything was right! Tonight I said "FINE!" and tore off all the caps and resistors and even the sim card holder and threw them all away and started over. I traced my connections and one again knew everything was routed as shown in the schematic. With that I re installed new resisters, caps, and a card holder. I powered it on and I get voltage and a connection to the network. I have no idea what was actually wrong but I really don't care. Keep on trying, the feeling of having working is worth it.

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