I am creating a remote-controlled wireless vehicle. It contains an Arduino Uno and a Raspberry Pi. The RasPi creates a WiFi network through which the vehicle can be controlled. The RasPi is connected to the Arduino via USB and gives Serial commands to it.
I am looking for a power source that realiably powers both shields (Arduino Uno and Raspberry Pi) at the same time. (The motors are not the issue here, they have a separate power source. The Raspberry Pi, on the other hand, carries a WiFi USB key which presumably takes quite a bit of power.)
A friend suggested a power bank, the kind of batteries you can recharge your phone with on the go. I am particularly interested in this product (sorry link is in german). It has two USB outputs and can output 2A at 5V. Capacity is 13000 mAh.
The problem is that the Arduino's USB port is taken up by the Serial connection between the RasPi and the Arduino.
Is there a good way to use such a power bank and use some kind of adapter to go from USB to the DC jack of the Arduino?
I read somewhere that the DC jack of the Arduino needs at least 6V. Will 5V be too little?
Different idea: Only the RasPi is connected to the PowerBank. The RasPi in turn powers the Arduino through the USB cable that is already in place for the serial connection. Will 2A / 5V be enough of a power source for this?
If none of this can work, what are the options?
(I could use two power sources, e.g. 9V batteries, but I read that thei capacity is really bad. That is what I like about the power bank idea!)
The UNO has an input voltage limit of +6-20vdc.
There appears to be an onboard 5 volt regulator that powers the UNO. The suggested input voltage is +7-12vdc.
At 6 volts there may be an issue with the voltage regulators headroom and current draw, it may cause lower than 5 volts going to the arduino which could be fine or could not be depending on if you guaranteed need 5v on your output pins.
Atmel states 0-20mhz @ 1.8v-5.5vdc.
Which reads that you can power the chip with as low as 1.8v and run it at 20mhz.
Chances are it will work at 6volts just fine and there wont be an issue with the onboard voltage regulator dropping below 5 volts.
I suggest a batterypack from a hobbyshop (for remote control vehicles ;p), or if you dont care about looks and size use a rechargeable drill battery. Or make your own by paralleling rechargeable 9volts. You can make its 'mAh' rating as large as you want.
You can make the equivalent of the "powerbank" for a lot less money. LiPo batteries have the highest capacity, but I would suggest using NiMH batteries, because they are easier and much safer to charge. To reduce the voltage, use one of Pololu's step-down regulators (which are very efficient) to produce 5V for both microcomputers. Here is a list of their regulators, but #2177 would be adequate. Pololu - Step-Down Voltage Regulators
Edit: I just checked and Amazon has the "Anker® 2nd Gen Astro E4 13000mAh External Battery" on sale, marked down from US$ 90 to US$ 30. It is hard to beat that price, even build-it-yourself.