Interfacing GSM modules with 3.3v microcontrollers
I am in the process of designing a datalogger to record the use of specialist equipment in an automotive environment. To do this I am looking to use the GSM network to request small packets of data remotely from vehicles all over the UK which means I will need a GSM module/card integrated into the datalogger. Every GSM module uses AT commands to communicate with a microcontroller over a standard UART connection so it seems simple enough... However, every module I have researched has a nominal power supply requirement of 4v (3.3v - 4.6v) and when transmitting has a burst current of 2-3 amps, that cannot drop the supply voltage lower than 3.3v. I am working off a standard 12v cigarette lighter socket so I need to drop the supply down from a noisy 12-14 volts.
I am using a 3.3v microcontroller so my immediate impulse would be to use a 3.3v regulator to supply the microcontroller and the GSM module (at minimum operating voltage) but this leaves me with zero tolerance for any voltage drop caused by the transmission surge current.
I then thought I could use a common 5v regulator and a 3.3v to 5v logic level converter as this would supply the current to the GSM module leaving 1.7v of tolerance for a voltage drop while still being able to use the 3.3v microcontroller, but the module is rated up to 4.6v so again, not feasible...
I've never seen such awkward power requirements from a component before, I played around with custom voltage regulator circuits (as I can't find any standard 4v regulators with high enough current capacity) and shifting the UART levels with line drivers but my solution just feels a bit messy.
I am planning on using the M95FA-03-STDN module from RS (908-4120).
Does anyone have any advice/experience they can share about working with these modules?
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Interesting overview of the issues faced using GSM modules.
Your 'messy' solution may actually be OK. I searched "GSM" in DesignSpark and found this module (171-1860 ) which may simplify the requirements.
https://www.rs-online.com/designspark/open-your-lines-of-communication-further-with-the-arduino-mkr-family they use a 3.7V LiPo battery and state "MANDATORY to have a 1500 mAh or higher LiPo battery plugged all the time" so that may offer you an alternative solution.
Searching the web for solutions reveals many solutions for the problem and even some dedicated GSM supplies. Unfortunately, the powering requirements seem more difficult thanusing the GSM module!
@Boss Thank you for your insight, I feel more confident now that I am designing this properly. Development boards always make this a lot easier but I am looking to design my own dedicated PCB this time - although Arduino does have a great selection for initial experimentation, I may have to have a play. I will also see if I can have a look for reference designs online to see if I can make any further improvements to my circuit. Thanks again.