At ModMyPi we offer a range of different micro-development boards, which all require slightly different power sources! Some are very stringent in their required input; for example, the latest Raspberry Pi recommends 5V @ 2A as a minimum for stability, but some are more flexible, the Arduino can accept a range of voltage inputs (6 – 20V), and regulates this to desired level internally on board. Not only that, the boards themselves have different power input ports, and some can be powered at multiple points on the board! We’ve got a simple breakdown of what each unit requires! You can check the below tutorials on how to best power each device:
How do I power my Raspberry Pi?
The least complicated, but most stringent in terms of power requirement is the Raspberry Pi!
The latest version of the Pi 2 can be powered effectively in a couple of ways. Please note. Unlike the original Raspberry Pi Model B, the Raspberry Pi 2 Model B cannot be back-powered via the USB ports (or at least can’t be booted in this fashion).
Mode 1 – Micro USB Port (5V @ 2A)
The first, recommended and easiest way to power the Raspberry Pi is via the Micro USB port on the side of the unit. The recommended input voltage is 5V, and the recommended input current is 2A.
At ModMyPi, our standard power supply for the Raspberry Pi is 5.1V @ 2.5A. The reason for increasing the voltage slightly is to negate any voltage drop caused by excessive current draw. This is well within tolerance for Micro-USB, and from experience, we have found that this give the best stability for most applications.
The Raspberry Pi can function on lower current power supplies e.g. 5V @ 1A. However, any excessive use of the USB ports or even heavy CPU/GPU loading can cause the voltage to drop, and instability during use. The latest versions of the Raspberry Pi B+/A+/2 have a “low voltage indicator icon” to notify the user if there is a problem with the power. This is demonstrated below:
Most “standard” 5V Micro-USB mobile phone, tablet, and digital camera chargers should work with the Raspberry Pi, although we (of course) would recommend that you utilise a high quality dedicated Raspberry Pi power supply to get the best results!
Mode 2 – Via the GPIO
A more technical (and of course dangerous) way to power the Pi is directly via the GPIO. It should be noted that, unlike the Micro-USB port, there is no regulation or fuse protection on the GPIO to protect from over-voltage or current spikes. If an incorrect voltage is applied, or a current spike occurs on the line you can permanently damage your Raspberry Pi. At best, you’ll “burn out” some or all of the GPIO pins, at worst you can fry your Pi! So be careful.
To power via GPIO, you only need to connect 2 pins:
1.) Connect a 5V source to Pin #2 (5V)
2.) Connect the ground of that source to Pin #6 (GND).
A simple example of this is demonstrated in the image above. We’ve taken one of our USB to TTL cables and connected it to one of our USB power supplies. Just hook up the 5V to Pin #2 (Red cable), and the ground to Pin #6 (Black cable). The TTL cable’s 5V line is regulated and limited to 500mA, so there is some measure of safety using this device.
This process would of course be the same for a spliced USB to Micro USB cable, however we would recommend that you regulate the line voltage and current to negate any nasty stuff!
This method is useful for a range of applications, and a number of breakout boards offer this powering functionality via the GPIO using battery supplies. We therefore recommend that powering via the GPIO only be achieved via a protected source. An excellent example of powering via the GPIO is our own UPS PiCo HAT, an uninterruptible power supply.
Mode 3 – Via the USB Ports
We did mention earlier that the new Raspberry Pi 2 & B+ can't be back-powered via the USB ports due to new regulation on the boards. However, this is a bit of a half-truth, as it "can" be done in a roundabout way.
If you apply power to the USB port when you Pi is off, it will not boot. However, if you apply power to your Pi via one of the standard methods (e.g. the micro USB port), then apply power to USB ports and remove the original supply, it will stay on and functional.
It should be noted that USB ports have a current limit of 500mA, so we would not recommend you attempt to supply more than this via the USB!