Steve Kosmerchock built a small light weight rocket timer for a friend of his. He is selling them for $40 on the XAVIEN web site. If you want to build your own Steve provides the schematic and firmware for free on his site. Have a look at some of his other PIC projects.

Steve explains how the project started, “A co-worker of mine wanted a small timer that ranged from 1s to 15s depending on what the user selected. They wanted to use a set of 4 dip switches to select the time. Needed to be as small as possible (weight being very critical) and run off of a 9V battery. Needed 2 failsafes to prevent accidental ignition of the second stage of the rocket. The following information is the end product of those requirements. You can buy IMPROVED single and dual stage rocket timers from XAVIEN .”

Source: PIC Guide