It has a 3.7v – 4.2v voltage requirement. So I created a simple buck regulator using MIC4576 regulator according to it's schematics and adjusted it's output to 4.2 volts. It can provide 3A of current. And i powered it through my laptop charger, so there's no shortage of current in the circuit.
But the module(sim800l) resets as soon as it finds a network(it's my guess). If I run it without sim, it runs fine and doesn't reset.
I've also tried 2 18650s in parallel to be able to provide atleast 3A to the circuit. But it still resets after a few seconds.
Is there anything obvious I'm missing?
Best Answer
Everything you are reporting is consistent with insufficient power to the GSM module, when it tries to register with the network, even though you think your power supply is OK.
The lack of an oscilloscope means that, using a multimeter instead, you cannot know the true voltage for any short dips (or spikes) due to the low sampling rate of multimeters. (Oscilloscopes have limitations too, but with their much higher sampling rates then for issues like this, an oscilloscope is usually sufficiently fast to show the necessary detail.)
That result tells you that you do need to investigate the power delivery to the GSM module further, as the voltage at the module could actually dip lower than the 3.8 V reading you have reported, for the reason that I explained above.
Not necessarily true. Depending on exact construction method, component layout, and component choices, I could make a buck regulator which will not provide the maximum current which the switching device itself (in your case, the MIC4576) is capable of. Or to say it another way: You need to prove that the power supply is really capable of supplying that voltage to the GSM module - you cannot assume that a 3A switcher, in a home-built design, is actually capable of supplying its full "off load" voltage, at the rated current.
The thickness and length of the wiring between the power supply and the GSM module, also affect inductance and resistance and so affect the power available at the GSM module.
Again, you cannot assume that. I have seen laptop power supplies which did not meet their claimed specifications (especially third-party ones from ebay etc.).
Some choices for you include: