Cheap GSM module (SIM800) not connecting to the network

[OleW]

Hi,

I have been working some years with the SIM900 which is similar to SIM800 (got one of
these too but haven't tested) and the problem with not registering to the network depends on the network operator.

The SIM modems (800 /900) does NOT support 3G/4G only 2G. So if the network operator request to use the 3G network for startup (this is determid by the operator when programming the SIM card) it will not be possible to register.

I have tested with many different SIM cards around the world and this seems to be the logical explanation (I have also contacted SIMCorp to see if any commands could be use to change the startup and force the modem to regsiter). If you select a network operator the use 2G for start up (I have seen
af patterne that pre-paid SIM card often work - guess they are setup to be used for any mobile device).

[juan3211]

Hi,

Does anybody use this kind of modules with a power supply of 5V and a simple DIODE ? How long ?

Thanks a lot.

[geologic]

Don't use a diode unless your power supply is very stable.
i've used that module with a external power supply regulated to 4.95V with a diode to down voltage to 4.25V. Then i replaced the power supply for a pack of batteries (5.08V), after that i got strange behavior, sometimes SIM800 didn´t send any messages. I figured that at 5.08V, the voltage on the SIM800 was 4.35V that leeds to OVERVOLTAGE warnings. Better is to use a LDO or some external power very stable, around 4.2V

[juan3211]

Don't use a diode unless your power supply is very stable.
i've used that module with a external power supply regulated to 4.95V with a diode to down voltage to 4.25V. Then i replaced the power supply for a pack of batteries (5.08V), after that i got strange behavior, sometimes SIM800 didn´t send any messages. I figured that at 5.08V, the voltage on the SIM800 was 4.35V that leeds to OVERVOLTAGE warnings. Better is to use a LDO or some external power very stable, around 4.2V

Could be the real problem the fact that batteries can't supply the 2A peak that SIM800L could need sometimes ?

Regards,

[geologic]

Not the case. as soon i replaced the diode for a 4V LDO, everything went to normal.

Despites specs saying Sim800 can consume up to 2A current, in my tests i never measured more than 350mA. I'm using a regular multimeter and only use GPRS functionality, never tested with voice or SMS.

[Clemens]

It's not only about the Vcc power, pins need also a voltage divider. The serial port characteristic of the spec says 2.8 V max:

see p. 31 http://www.seeedstudio.com/wiki/images/4/46/SIM800L_Hardware_Design_V1.00.pdf

[juan3211]

It's not only about the Vcc power, pins need also a voltage divider. The serial port characteristic of the spec says 2.8 V max:

see p. 31 http://www.seeedstudio.com/wiki/images/4/46/SIM800L_Hardware_Design_V1.00.pdf

Yes, it could be. But sometimes these modules came with a voltage "translator" and you can use a 5V signals, but you have to be really carerful with power voltage, not to burn it.

May be a diode is faster o slower than others? (i don't know about this kind of problem)

Regards,

[geologic]

Yes, it could be. But sometimes these modules came with a voltage "translator" and you can use a 5V signals, but you have to be really carerful with power voltage, not to burn it.

Yes, mine is 5v tolerant, no need for level shifting

Maybe a diode is faster o slower than others? (i don't know about this kind of problem)

Regards,

for supplying power i think it's irrelevant, just use one rated for 2A or higher

[Andrea1970]

Today i received the same module with same problem. Red LED blink fast and typing AT+COPS? the answer is AT+COPS:0.
I powered the module with 3 D Cell with a DIODE, the voltage supply is about 3.9V=(4.5-0.6)V
The bheaviour are strange! Sometimes the module accept commands sometimes not! Can someone an give me tricks?
I think that i threw my money  away, not is the first time! In the past i tested more GSM module.
With TELIT i never had problems, but when i started to test cheapest SIMCOM (assembled by various/unknow Chinese company) it was a Hell! 900 ok, 900A don't run in Europe, 800L with direct connection (like reported by vendors) to 5Vcc of Arduino board (burn various LM1111). 
 

[geologic]

Are you sure you are powering at 3,9V? Measure it with a voltimeter when SIM800 is ON, i guess your batteries cannot mantain a steady 4,5V


I had one working for a month and suddenly it stops working. I was powering it with 4V but RX/TX lines were connected directly to 5V arduino ports.
I replaced by a spare one but this time add a level shiftter between arduino and RX to lower the signal to 2,8V. It is running now for 2 weeks without a fault.

For my experience, i advise:
1) Power SIM800 with a 4V LDO. Use a diode only if your input is very stable
2) Keep RX/TX lines below 2,8V

[elik745i]

Are you sure you are powering at 3,9V? Measure it with a voltimeter when SIM800 is ON, i guess your batteries cannot mantain a steady 4,5V


I had one working for a month and suddenly it stops working. I was powering it with 4V but RX/TX lines were connected directly to 5V arduino ports.
I replaced by a spare one but this time add a level shiftter between arduino and RX to lower the signal to 2,8V. It is running now for 2 weeks without a fault.

For my experience, i advise:
1) Power SIM800 with a 4V LDO. Use a diode only if your input is very stable
2) Keep RX/TX lines below 2,8V

Can you please attach circuit diagram. I also experience such problems, Used one SIM800L for a month, then is stopped registering in the network, when I pull TX line from SIM800L, restart the module it registers in the network, then put TX back and it works, then if I reset the Arduino, it resets the SIM800L and can't register in the network again. Looks like problem is with module's serial ports, will test another one with voltage dividers...

Strange thing is no matter it's registered or no, it responds and communicates with Arduino OK, displays found networks, but when I send command to connect to the carrier AT+COPS=0,2,"40001" for example it responds ERROR....why?

[zancos]

I had same problem with SIM800 module and the problem was the supply current.

I recommend:

1. Test SIM card in your mobile in order to verify if it is working properly (maybe the SIM card is damaged)
2. Try to supply the SIM800 with an stable source 4,1V@3amp. Its important to know if your problem is a supply current problem to discard any other issues.

In my case I used a DC-DC converter from 12V@2.5amp to 4,1@2.5amp and now it works properly. If the module is connected to a source without enought current, the SIM800 module will reponse to AT commands but all of these commands relationated with the SIM will not work.

[geologic]

Here is a sketch of my circuit.
Left side is the LDO that outputs 4V
R3 and R4 are a voltage divider to provide 2,8V. That voltage feeds the level shifter (1n4148 with 4,7k).
Only RX line needs protection, since TX will be always below arduino 5V limit.
For clarity i didn't connect TX ou RESET lines.

When testing, check SIM800 RX and TX pins, if they are around 2,8V everything is ok.

[elik745i]

The problem was, I think, faulty module, module got damaged most probably as I never used voltage divider between arduino and SIM800, after replacing module and using simple voltage divider new module working like a charm!

DO NOT USE THIS MODULE WITHOUT RX AND TX VOLTAGE DIVIDER!!!

[freman13]

I just got SIM800L myself, and have same problems with connecting to network. While SIM900 worked like charm this one is a bit stubborn.

I receive AT commands related with SIM as well, but I can't send SMS for example. Maybe it is not registered to network... Does this module needs to register to network manually every time?

Also, you mention Rx/Tx voltage dividers and zeners as must, but I've seen many circuits out there and demonstrated on Youtube that didn't use any of those and still works perfectly fine.