On that page there is a run of unhappy users blowing their regulators for having used > 4.2V. And some confusion, I guess, as to the propriety of using Arduino logic (0/5V) directly with the SM5100's 3V pins (probably not good.)
Some of the conversation:
UART 5V tolerant?
Driving from Arduino is 5V signalling, however this SM5100B is only operating at 3.8V… unless this module is specifically 5V tolerant on the UART pins(and I can’t see this in the data sheet…) then its a time bomb…
Anyone damaged UART on this module?
Interesting question, the datasheet says 3.2v is max.
“then its a time bomb"
I hate it if SparkFun sell such expensive things with errors on them
That’s the 2nd time I have fatal problems with this module.
The first time the GSM module was burned. I got in contact with Nate and he asked me to measure the voltage output of the SPX29302. I did and it gave 3.98V. So Nate said the regulator was damaged and overheated the GSM module.
Today I soldered the second shield and I removed the GSM chip. I attached the shield to arduino duemilanove and start measuring the output voltage of SPX29302. Now it outputs 4.00V !!
It can’t be a coincidence. Something is wrong.
I just measured mine and it gave me 3.94.
It says up to 4.2v is okay, but is that just BS?
And should I not use it at 3.94?
“3.3V to 4.2V range, 3.6V typical”
Sorry about the confusion. As per page 9 of the manual the module can operate at a maximum of 4.2V.
We use resistors with a 1% tolerance on the resistor divider that sets the output voltage of the SPX29302 regulator. So the output voltage should not deviate greatly from the 3.8V it is set for. This means if you are seeing a 200mV rise in output voltage, there is a chance you have damaged the regulator.
Sleahey | about 2 years ago 1
If the data sheet says its fine upto 4.2V then its fine…
With the components fitted, at 1%, if you read the datasheet for this regulator, you will find the expected output range is
So, you could say that the 3.8V on the datasheet is wrong, but its close enough… in engineering terms..(+/-10% as a general rule is OK!)
If your worried, change R1 to a 20K, which will bring the nominal down to ~3.7V
Also, I would recommend replacing the link on the RX UART with a resistor, maybe a 2K2 (0402), to protect the input from 5V signalling…
I used this…
Mine has the same problem :‘( It worked fine but now it doesn’t. I even notice some marks on the stickers so it seems to really overhet the SM5100B. But… how come it does that. The datasheet says it should be able to handle up to 16V input. I 'only’ used 12 (5A adapter). So how can we damage the regulator?