How to properly power sim800l module?

Question

I have this sim800L module

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?

Answer 1

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.

Do you have access to an oscilloscope and experience using it?

I don't have an oscilloscope :(

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.)

But I've measured the voltage when it's powered and I've noticed that voltage drops from 4.2v to about 3.8v for a brief time when it restarts.

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.

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.

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.

i powered it through my laptop charger, so there's no shortage of current in the circuit.

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:

• Use a friend's or colleague's known-working GSM module + power supply setup, and substitute just your GSM module (i.e. use their known-good power supply).
• Try using shorter and/or using thicker wires between the power supply and GSM module, to reduce the voltage drop there.
• Get access to an oscilloscope to perform further measurements.
• In some cases (especially with marginal power supplies, long power cables etc.) adding extra capacitance on the GSM module, can help during the high-power GSM transmission bursts. A remote possibility is that you have a defective GSM module e.g. that large tantalum capacitor on the "stock photo" you gave, might be faulty.

Answer 2

General considerations regarding powering and interfacing the module, not related to OP's issues most likely.

The module requires 4.0V nominal (recommended) with up to 2A peak consumption and as low as a few mA when idle.

Forget about using a voltage divider. You would need to burn hundreds of watts in the divider to get reasonable regulation over that range.

You need a voltage regulator. A switchmode module based a chip such as the XL4016 would work, however the SMPS noise might interfere with the radio. The LM2596 modules are a bit marginal in terms of dropout voltage.

A linear LDO regulator capable of handling 2A peak with less than 1.2V dropout is possible, but they tend to be a bit expensive.

As well as the supply voltage you need to ensure inputs are kept within the safe range. You can use a voltage divider to reduce the TX output of the AVR to a safe voltage.

Source :How to drop voltage to 4 volt from 5 volt source voltage with resistors?

Answer 3

I was using a reasonable 2.5A bench power supply to feed my module, and sending AT to the module received OK back as expected.

However, sending commmands which required network access (ie transmission from the module) often resulted in a reply from the module of ERROR.

I added a 1uF and a 22uF electrolytic close to the module and it now works reliably. Then I checked the datasheet, it recommends 10uF, 33pF and 10pF close to the module (these may be on the PCB in the stock image) to supply the peaks of current required during transmission.

A high current bench supply may not be able to change its output current rapidly enough to supply the bursts of current required, resulting in erroneous transmissions.

Answer 4

OP is a typical case of the module not getting enough juice.

Sorry for the non-technical answer, this answer is only through my experience.

If you want to get it running for sure, feed the module with a cheap DC-DC buck converter, those regulable with the trim pot using a LM2596S. They have a 220uF 35V capacitor at the output. Regulate it to approx. 4v and add another capacitor to the output. I'm using a 3300uF 6.3V. It's kind of big but they are cheap anyway.