I have a SIM900 shield that I want to control with a Raspberry Pi. I want to use GPIO pins on the pi and UART pins on the SIM900 shield. If I understand correctly the numerous tutorials available, people usually power the pi and the shield with separate power supply (USB for the pi, 2.5 jack for SIM900). Isn't it a way to power the shield from the pi with one of the power pins?

There is the documentation of the shield I use.

  • \$\begingroup\$ GSM Modules are power hungry like 1A-2A @9V. Pi cant drive it. \$\endgroup\$
    – Mitu Raj
    Feb 28, 2019 at 12:06

1 Answer 1


You can wire the single power supply to the shield as well as to 5V pin on the GPIO connector of the RaspPI.
Some PI's have a fuse protection. In order to not circumvent this protection, an even better suggestion is to use a mini USB, cut it, isolate the 5V and GND wires and connect those to the single power supply.

Better not to use the mini USB to supply the RaspPI and wire the 5V pin to the shield, as the (unknown?) current drawn by the shield runs over the RaspPI. This might cause noise maybe too much current run through the RaspPI PCB traces.

The SIM900 chip partially requires currents of up to 2A, which the Arduino cannot afford.

The RaspPI neither can afford this.

  • \$\begingroup\$ I read somewhere it is not safe to power the pi through the 5V pin because it bypasses the fuse used when it is powered by USB. What is your opinion? \$\endgroup\$
    – Nautigsam
    Feb 28, 2019 at 10:40
  • \$\begingroup\$ Good point. I updated my answer. \$\endgroup\$
    – Huisman
    Feb 28, 2019 at 10:45
  • \$\begingroup\$ I am completely new to electronics, then the next question could seem a bit odd: we are talking about voltage but does current has to be considered as well? If the power supply provides "two much current", can it damage the pi? \$\endgroup\$
    – Nautigsam
    Feb 28, 2019 at 10:52
  • \$\begingroup\$ @Nautigsam - The rPi will only draw the current that it needs from the power supply. So if the rPi wants 850 mA the power supply must be able to deliver at least that much current, but it will not damage the rPi if the supply can deliver more than that (i.e. most recommendations for rPi power supplies recommend a power supply rated at 2500 mA). \$\endgroup\$ Feb 28, 2019 at 10:58

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