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Topic: SIM800L pinouts / network problem (Read 17781 times) previous topic - next topic


I've bought a cheap Chinese SIM800L breakout module as below

I can power it up and get responces to AT commands but it doesn't seem to want to connect to a network (I'm in the UK and have tried the T-mobile sim from my phone and just bought a Vodafone sim but no joy). 

I've hooked it up as follows

module / arduino
5V / 5V
VDO / not conencted as I don't know what it is
TX sim / RX
RX sim / TX
RST / not connected as I'm assuming I don't need it and don't know where to pull it low or high anyway

Should these things automatically connect to a mobile network or do I have to do some configuration via AT commands?

Does anyone have any idea what the VDO pin is?


SIM card was in upside down.  Now connected to the Vodafone network without me having to do anything.  Just trying to work out how to send a text message now!

"VDO" turned out to be "VDD" and I assume it is for connecting 3.3v lipo to, bypassing the 5v regulator?


Hello MrCanBus,

I have the same and I'll run it soon
I'm used to SIM900 and I do everything with AYES command, no library
have you progress to use this GSM SIM800L
Have you any advice / tips to manage it ?



I bougth a SIM800L from aliexpress

It works perfectly. I don't use libraries. I connect the sim800L with my server (MySQL) through a Java service I made (ip and port)

Some error I got at the first try:
- Put the micro sim correctly.
- Check the voltage (3.5 - 4.4 v). I use an voltage regulator in 3.7v.
- Test the sim800L with a simple code. I test the AT command by keyboard.



I have same board described in first post, not connecting to network.
changed sim cards, no effect, NET led is blinking almost twice in a second, RING led is blinking every 10 seconds or ON all the time, No response on AT commands, SIM card number unreachable when i call from phone.



You should try to connect both GND pins to ground. I have the same behavior and after I connect the second GND to ground, the module starts working.

Also I have problems with the reset pin. My Arduino cycle restart if I connect the reset from Sim800 to reset on Arduino. I think it's because the voltage. So i bought a level converter to connect them.


Check the power supply. The SIM800 sometimes draw more than 1 amp, like when you start a call.

I test 2 diferent modules, put a common use diode, it draws about 0.7 volts, and atach to a 5 volts with 2 amps min. I test it with a computer power supply. Dont conect to 5v directly unless the board have voltage regulator!! it fries the module.

I have a lot of problems when i start to test it, but with that conections and the diode i can make calls and send sms.

With the module conected to a 5v like the Arduino power supply, it power up, but NEVER connect to a network, maybe you can comunicate with it with AT commands, but it will reply only symbols or ERROR messages.


Sorry, my answer is for the second pic module.

For the first pic module, atach it directly to 5v with more than 2 amp power supply. Maybe the current draw is your problem.

I dont think VDD is for a LiPO, that board doesnt have a step up power supply.


Did anyone make this module work? I'm having troubles to register in my op networl


Apr 28, 2017, 08:48 pm Last Edit: Apr 28, 2017, 09:36 pm by geoFun
From someone who has this working I'd be interested to know what the normal LED sequence is from power on?

In my case D2RING comes on, NET flashes quickly 7-9 times, then both LEDs go off, then that sequence repeats.

I have managed to send a text (in fact a few Flash Texts :-p), but I'm having less success as time goes on... The board is marked "5VIN", so that's what I've given it, though from what I read that might be a mistake...

Edit: My bad, I had fallen into relying on the FTDI programmer for power, which din't give the power the SIM800L needed via an 'Adjustable XL6009 Step Up Boost Voltage Power Supply Module Converter Regulator'. So now D2RING stays on and NET flashes every 3 seconds. Back making progress...

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