The 2009 rocket flying season is nearly over, and I haven’t had a single flight all year toward my GPS-guided rocket recovery project. I’ve been too busy with business stuff to work on it, but my goal for this winter is to get the new “Rev4” PCB up and running, ready for flight in the spring.

For that, I’ve decided to shift from the PIC18 to the MIPS-based PIC32 parts.

Which means I’ll be porting over a lot of code from the PIC18, so now seems a good time to post my long-promised source code and schematics for what I’ve done so far, which I plan to do in the coming days.

For now, here is a Excel spreadsheet with the PIC32 pinout for the 64 pin TQFP parts. Each time I do a MCU-based design, I make a table like this for allocating MCU pins by function. If you’re working with the PIC32, you may find it useful for the same purpose.

Click the image to download the .XLS file.

PIC32MXx40 pinout

I just finished building this tiny rocket altimeter.  It fits inside a standard 18mm (diameter) rocket motor case – in this case, a used Estes C6-7 motor.

It’s based on Robert DeHate’s PICO-AD4 altimeter.  It measures peak altitude and will fire the ejection system at either apogee or a main deployment point (a few hundred feet AGL).

The most difficult thing was finding an adequate battery that would fit – I ended up with a L1016 6v alkaline; they are widely available (online) and inexpensive.   It uses a 220 uF capacitor to fire a AG1 flashbulb for deployment (220 uF is enough to do this reliably).

Here’s the schematic – not much to it:

I drew a power switch, but I couldn’t get it to fit.  So I just take out the battery to turn it off.

I made the hole for the battery with a Dremel tool.

Here’s the back side:

The jumper on the back (J1) selects whether the ejection will happen at apogee or using the main deployment point.

The two bolts/nuts on the end are the attachment for the AG1 bulb (2-56 hardware), the battery clips were made from parts in my junk box.  The negative terminal is soldered onto two cut-off pieces of paperclip (paperclips are made out of good-quality steel), which are in turn soldered onto the perfboard.

(By the way, I’ve discovered the perfect tool for cutting PCB traces – a little battery-powered engraver. Harbor Freight sells the one I use for less than $10.  Just make sure you blow away all the tiny copper pieces afterward with canned air.)

The resistor is just to limit the charging current on the capacitor – that little battery really doesn’t like high currents.  The resistor value is not critical – anything from 500 to 3000 ohms or so should be fine.

Here’s a top view (with it running and the LED blinking):

The 220 uF cap is held in place with some hot glue (as are some of the wire-wrap wires on the back).  I used epoxy to hold down the jumper, screws and base nuts and to reinforce the thin bits of perfboard next to the battery – otherwise the whole thing bends too much under the off-axis tension from the battery springs (I broke an earlier version that way).

Here it is snug in it’s 18mm motor case:

The flashbulb wires are meant to go out the other end, thru the rocket nozzle hole.

As you can see, I had to ream out the inside of the motor case a bit to get things to fit.  (This was desirable anyway, to get out all the black soot left after firing – do NOT try this with a unused motor!!)

The reaming was done starting with a 1/2″ drill bit, then a 9/16″, finishing with sandpaper wrapped around the 9/16″ bit (use some double-stick tape to keep it on there).  It helps a lot to have a drill press.

I haven’t flown it yet, but it works well on the workbench.