Components
Because the hardware would end up being shot into the air with an unknown but large force and a few seconds later return to air at an unknown location, with an unknown but also large force, there was no guarantee that the electronics would stay intact or even be found back. That's why I decided that I'd have to keep the design as cheap as possible, as well as as small and as sturdy as I could manage. I was somewhat on a small timeframe, so I decided on using parts I already had or could obtain quickly.
I ended up using these components because I already had them lying around: For the microcontroller, I used an ATTiny13 microcontroller. Roomy enough to program a data logger in and even in its 8-pin DIL version small enough to fit in the nose of a model rocket. The uC would log its data to an 24C256. This is an i2c-accessible piece of EEPROM which can contain 32KByte of data. This should be roomy enough to measure the flight of the rocket with enough resolution to look good when graphed. The i2c-interface means we'll only waste 2 of the ATTiny13s 5 I/O-pins to connect it, and the chip being EEPROM will make sure we can retrieve the logs even if the rest of the hardware has crashed into the concrete and is completely broken.
I didn't had a 3-axis acceleration sensor, so I had to obtain that. The
local electronics store didn't had one cheap enough, so I decided to improvise.
While everyone may know the WiiMote has an acceleration-sensor in it, it
usually costs something like 40 euros, which was a bit much for something that
ended up getting shot in the sky. Luckily, the accompanying Nunchuck also has
an acceleration sensor, and the local games shop could sell me a knock-off
for E12.50.
When I opened it up, a nice surprise awaited me. First of all, the sensor
itself was a Freescale MMA7260, which is a well-known chip.
Second: the difficult-to-solder sensor chip already was on its own adapter board!
I only had to desolder it and then I wouldn't have any trouble connecting anything to it.
Ok, with all the components obtained, let's build a datalogger!