The Arduino — and AVRs in general — have a wide range of power supply options ranging from around 1.8V to 5.5V. The choice of voltage is usually determined by the desired clock speed or power consumption requirements. The Arduino and its many variants have power jacks that allow connections from big, clunky “wall warts.” Alternatively, some boards can get their power from external power supply pins, either regulated externally or on board. But what about if you’re in a parking lot at a convention or coffee shop and want to show your geeky friends your new Arduino or AVR-based invention? Well, I’ve got an answer for that!
Step 1 Bill of Material
What You’ll Need
As I mentioned in the intro, this project has very few requirements or external components. Here’s what you’ll need:
- Auto power plug (www.mouser.com #171-A1378-EX $2.33)
- 0.1uF 0805 capacitor (www.avnet.com #08051C103JAT2A $0.09)
- 0.33uF 0805 capacitor (www.avnet.com #0805YC33rKAT2A $0.04)
- 1uF 0805 capacitor (www.avnet.net #08053C105KAT2A $0.10)
- 5V regulator DPAK MC7805CD (www.avnet.com $0.22)
The PCB I designed can either be etched by you with your favorite PCB creation method, or alternatively, you may send the gerber files (which I include) off to a fab house, in my case, www.seeedstudio.com Fusion PCB service for professional fabrication on the cheap. I got 20 excellently produced boards for $10. Its really hard to beat, especially when you’re working with small SMD components, but it’s entirely possible to etch these boards yourself, if you’re so inclined.
Besides the items mentioned above, you should have a soldering iron, solder, maybe some flux, tweezers, wire cutters, snippers, crimper, etc. But you probably already have this stuff laying around.
Turn the page to get started on the design.
Step 2 PCB Design
There is a small space within the auto power jack shown in step 2 that can fit a small PCB. And yes, I do mean small. The board should measure really no larger than 29mm x 10mm (although my board is exactly 29.21 x 10.16 mm). This size really screams for the use of SMD components. Luckily, we can use SMD packages that are small, but not too small for us to work with manually.
The design here is very simple and follows a standard linear power regulator setup. We take in the 12V or so from the car and pass it to a 5V linear regulator with a few capacitors attached to handle transients and unwanted frequencies, helping to reduce ripple voltage in the output. Finally, we output this regulated 5V through a set of wires that will connect to the Arduino or AVR board.
Schematics and Board
Check out the included pictures of the schematic and board to get an idea of how this is all setup. It’s very straight forward and shouldn’t offer too many surprises for those of you that have built your own power supplies for microcontrollers before. Also, find attached the actual schematic and board file (*.sch and *.brd) for use in Eagle, if you want to change or modify anything. Finally, if you do choose the option of having your board custom fabricated, I’ve also attached a zip file of the necessary files you will need to send to Seeedstudio to have them build the PCB. From time of order to the time I received my PCBs was about 2 weeks. Cheap and speedy.
Step 3: Build It!
Ok, this is, of course, the fun part. Now we build our vehicle-based Arduino power supply.
Solder PCB Components
I started off by soldering the components on the top of the board. This includes the 0.33uF capacitor and the MC7805 voltage regulator (in DPAK package). I found it helps if you pre-solder the pads, as shown in the picture below. Then you can use tweezers to place the capacitor over the soldered pads and use your soldering iron to melt the solder and secure the capacitor in place. Same goes with the voltage regulator. You may want to add a ribbon of solder around the top edge of the voltage regulator after its been secured.
Read more: Power Your Arduino From Your Car