Many times while traveling, I have had the need to debug my firmware on a circuit board. Unfortunately, I was not carrying a power supply. So in turn, I had to wait until I reached my lab before I could power my circuit board to test the new firmware. This new innovative project, the USB Based Variable Power Supply, will solve this issue effectively, affordably, and reliably.
A quality power supply is crucial for anyone who is into computer engineering but most variable power supplies are AC/DC, which are large and very inconvenient to carry while traveling.
VariPower-USB-500A is open source hardware. All hardware design files and firmware source code are released under the GPL v2 license. It's a great way to get started with electronics!
Download file: http://www.etonnet.com/download.aspx
Originally I used an LM317T 3 terminal regulator to build the first prototype. It works, but I found the voltage drop under a load is too high. Obviously, this is not a good solution for the USB based variable power supply, since the max voltage for USB power is around 5V. If the output voltage drop is too high, it doesn’t meet the developer’s requirements. After I compared a bunch of different regulators performance and cost, finally, I chose MP1401 as the voltage regulator chip. This chip has a very low voltage drop (around 0.17v) under a load, plus it supports high current output; although the max current for USB is 500mA, using an external AC/DC USB adapter it allows higher current power output (up to 2A). MP1401 also supports a wide input voltage. With the same PCB board, we built one universal battery charging station with a 12V input. The output voltage is adjustable so It can charge a single cell li-ion battery or multiple serialized li-ion batteries. To help the user easily find the output voltage, I provided a “3-digit” segment LED to instantly display the real time voltage. An R8C 16 bit Renesas microcontroller is used to monitor the voltage with 10mV accuracy.
For most circuits, 1.2v to 5V voltage and low current is enough. In case a user needs higher voltage or higher current output power, then an additional USB based AC/DC power adapter is required.
Now, I carry this portable power supply in my laptop bag all the time . I can use it to power most of my circuit boards. I can use it to quickly check LEDs and find any that are malfunctioning. I am also considering the addition of a new feature in the firmware to turn this unit in to a USB based voltage meter as well. I find this is a very useful device and I hope you will too.
Please support this project and get power for your Arduino, BeagleBoard, Uno32, chipKIT Max32, hacks, and any other circuitry projects you may have.
By the way, the T-Shirts look great, here's a peek:
- (15 days)