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My current electronics project is to build a very simple customizable "phone". It is my own idea, with as ultimate goal to learn about microcontrollers and basic electronics.

This is my set-up so far

Project set-up

I managed to interface with the microcontroller, and the voltage transformation circuit seems to works (how do you call this?). The issue is with the Neoway M590 GSM modem. It reboots every couple of seconds. I think this is because the modem draws a peak current when trying to connect to the network a few seconds after starts-up, and automatically shuts down because the voltage drops too low for safe operation. This is why we need the big capacitor there (1000 uF). I power the board with a PSU that can supply more than enough amperage. Communication is via a USB-TTL converter which I connect to a computer.

Please note that in my set-up I have completely eliminated all dependence on the microcontroller and voltage transformation circuit, in an effort to isolate the problem.

The Neoway M590 came with a pre-designed PCB

Neoway M590 PCB, front

Neoway M590 PCB, back

I have soldered one of these PCBs with a Neoway M590 and had no modem restart issues (after I put in a heavier capacitor).

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    \$\begingroup\$ Your wires are not up to delivering the kind of peak currents legacy GSM needs, and your capacitor is not sufficient or sufficiently connected either. GSM modules are really intended for direct connection to a suitable battery - it's what the reputable vendors of hobby modules configure for. \$\endgroup\$ Apr 25, 2019 at 18:27
  • \$\begingroup\$ Maybe it's just me, but I don't see how any of the power rails on the right half of the proto board are connected to +/-... It would help if you made an actual diagram of what you have hooked up, looking at a picture of a proto board with wires all over the place is near impossible to understand/diagnose. \$\endgroup\$
    – Ron Beyer
    Apr 25, 2019 at 18:35
  • \$\begingroup\$ Mobile phone design usually uses multicore ARM processors and complex telephony software to run GSM. Phone design involves hundreds of seasoned hardware and software professionals and years to complete the task. This is NOT a beginning hobbyst project. \$\endgroup\$ Apr 25, 2019 at 19:07
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    \$\begingroup\$ @Ale..chenski This is a DIY all-in-one GSM modem with a relatively simple interface. I would not give it as a project to an absolute newbie, but it is not that big for someone who have done couple of simple projects before. \$\endgroup\$
    – Eugene Sh.
    Apr 25, 2019 at 19:32
  • \$\begingroup\$ Instead of breadboarding you should solder the modem on the supplied PCB, and put all three bypass caps on (100pF, 0.1uF, and 100 uF). The module consumes peaks of current up to 2 A. \$\endgroup\$ Apr 25, 2019 at 19:51

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The problem is quite likely related to your breadboard. They are not very good for high currents.

Why? Well there are a few reasons, but it all comes down to your components not being that well connected.

Firstly you inevitably have a bunch of thin wires going between everything. I highly doubt your average jumper wire is rated for 2A. But even if it is, we still have some other problems.

Then, each of those wires and components are only softly held by the hole in the breadboard. How much surface area of the lead is actually in contact with the conductor? Potentially not very much and this is repeated multiple times along the current path.

Finally there is the path between each hole on the board. We don't know how good that is, but it's also probably not designed for a very high current.

So all these little things are going to add up along the current path and when you finally reach your component, there simply isn't enough power for it.

What can you do? Well you could try re-arranging your breadboard to mitigate the issues. But really you are probably best off just building the PCB and soldering wires to it which you can then connect to your micro-controller on the breadboard.

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THese breadboards were invented long before GSM was even thought of nor high speed PIC uC's.

They are not really well-suited for any RF or high transition speed CMOS uC operating with 10ns risetime. Back in the 70's CMOS was slow and putting caps next to each IC usually worked.

However, you have huge loops longer than your antenna and no decoupling cap on the PIC.

So, make sure you respect the inductance of 0.5~1nH/mm. For risetimes and V=LdI/dt that means 1nH/mm-ns * dI means the transfer function is 1 volt drop per nanosecond risetiume per mm length times change of current in that rise-time.

Rule of THumb for a trace length to width ratio if @ l/w = 10, L=0.5nH/mm then @ l/w=80, L=1.0 nH/mm

OK if that doesn't make sense, your ground power loops are a big lousy antenna.

Just don't use the breadboard DC rails for anything except LEDs and risetimes > 0.1us and not to power a GSM radio unless a low ESR ceramic cap is added directly across the supply pins.

High speed data only works with twisted pairs of AWG24 hookup wire or magnet wire soldered to a resistor.

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