The new USB Power Shield boards (rev. 2.0) have just arrived from BatchPCB! As always, they were quick, great quality, and they even sent me a few extra! Awesome service.
Version 2.0 has some major revisions since v1.0, including:
- Smaller Size – cost is determined by size, so I brought it down to the bare minimum – just enough to cover the Arduino pins.
- Power Planes – Added a 5V plane on top and a GND plane on the bottom to increase the reliability of the design, allow higher current, and also act as a bit of a heatsink
- Thicker Traces – the traces in v1.0 are only 8mil, which is pretty small and is really only good for about 200mA. Some devices powered here may need more than that. To support the USB spec of 500mA per device, I’ve bumped up all the traces to 16mil. There’s plenty of space for traces anyways.
- Remove the Vin LED – unnecessary.
- Flush caps – leave space so the caps can be bent down, so another shield can be fitted on top of this one. The regulator is also mounted on the edge to allow bending it down, although in many application it will need a heatsink so they may not clear even when bent down.
Keep in mind not all parts on the board are needed. For instance, if you’re powering a single pair of lights (or anything running at <300ma) you can just use the Arduino's built in DC-in with voltage regulator (USB power alone is not going to cut it). If that's the case, you can leave out the 7805 regulator, the 100uF capacitor (keep the 10uF), and the power diode D1. You also don't have to have the power indicator LED or its resistor RLED. And if you're only controlling one device, you only need one relay and one USB connector. All in all, you can get the parts cost for this board down to about $4 at the minimum configuration. If you want to go all out, here's what you'll need:
2x G6JU-2P-Y-DC4.5 Relays @ ~$2.85 each
2x USB A connectors @ ~$0.45 each
1x 7805 5V Regulator @ ~$0.37
1x DC-in 2.1mm Jack @ ~$0.63
1x 100uF 25V capacitor @ ~$0.03
1x 10uF 25V (10V ok) capacitor @ ~$0.03
1x 1N4004 standard Diode @ ~$0.04
1x 450-500 ohm resistor @ ~$0.04
1x 6x6mm pushbutton switch @ ~$0.24
1x 5mm LED (any type/color is fine) @ ~$0.08
1x 28+ pin row .1″ male header @ ~0.11
Total parts cost ~$8.17
You’ll also need a heatsink for the regulator if you plan on drawing more than ~200ma from it, those can range from $0.30 to $2, depending on size and complexity. There is a quite large one in the picture above as I was using it to charge my MP3 player, which draws a lot of current.
Stay tuned for an assembly guide. Also, I’ll be selling the few extra boards I have at cost to those interested, details to come soon.