April 23, 2007
Our finalized circuit board
Early in the project, I decided it would be a good idea to design an entirely new blimp control board, so that we would have a lot more control over what happens onboard each blimp. For projects like this, it is definitely good to see whether you can just purchase a canned solution, or if you will have to build it completley from scratch. Choosing either extreme is probably a bad choice.
With this PCB design and the accompanying firmware that runs on it, we ended up a little more on the "from scratch" end, but now hopefully others can leverage our work. We used expressPCB to produce our boards for a very reasonable charge, accompanied with fast delivery. Our final design is available for download. You'll need the (free) design software from expressPCB to open and manipulate the designs. An accompanying schematic is also available.
Now, in terms of features, this PCB has a quite a lot packed into a relatively small package:
- Onboard Microchip PIC18F1330 microcontroller, able to run at 32MHz with its internal oscillator. Beware of this inaccuracy in the currently-posted PDF manual!
- Serial communications with pins designed to mate with the Sparkfun BlueSMiRF. This allows the unit to operate remotely with very low power at a distance of 100 meters!
- Speed and direction control for 3 DC motors (400mA).
- Motor source voltage is separable from the main battery voltage -- so you can use different batteries to match your motors. If you don't need this, you just jump the main battery over.
- Two mutually-exclusive high-power outputs (400mA). We use these for two high-intensity LEDs.
- 0.01V-precise battery voltage sensing down to 3.0V.
- Pins designed to mate with an HMC6352 compass.
- Another pin set alternately compatible with this 3-axis accelerometer.
- Pin header for In-Circuit-Serial Programming with the Olimex PIC-MCP-USB programmer, which is compatible with the Microchip MPLAB.
- The whole thing weighs less that 15 grams populated, and measures just under 2.5" x 1.9".
Not bad for a first hack at a PCB, right?
Posted by jrpowers at April 23, 2007 11:34 PM