So I'm in the process of building a rocketry altimeter for fun. I used to do a bunch of high power rocketry stuff as a kid out in the Anza Borrego desert. Tons of fun and all that. One thing that I never really got around to playing with was altimeters.
Now that I've got a fair bit of electronics knowledge under my belt I thought I'd take a crack at designing my own. I've got the microcontroller, accelerometer and pressure sensors figured out. Data logging to a flash chip is straight forward enough. One thing I don't have a ton of experience with is blowing the ejection charge in a reliable manner.
Usually on the altimeters we'd use there's one charge blown at the top for a drogue chute and the one at 1,500-500ft for the main chute. Ideally I'd like to be able to pre-charge some high volume capacitors from a single 9v battery and provide enough amperage that I'm sure they'll fire. A common problem we'd encounter is that the drogue would fire fine but then the battery would be too weak to provide current for the main after a couple uses.
My current idea is to use a single boost step-up dc/dc converter to step 9V to 25V and store that in a pair of 470uF Aluminum-Elec caps and then use a transistor to control discharge. I simulated this in SPICE and I get about 500ma for ~100ms which should be enough, however I was wondering if anyone knew of a better way to provide a short high current burst. Usually when we fire igniters on the ground it's from a 12v car battery or similar.
Now that I've got a fair bit of electronics knowledge under my belt I thought I'd take a crack at designing my own. I've got the microcontroller, accelerometer and pressure sensors figured out. Data logging to a flash chip is straight forward enough. One thing I don't have a ton of experience with is blowing the ejection charge in a reliable manner.
Usually on the altimeters we'd use there's one charge blown at the top for a drogue chute and the one at 1,500-500ft for the main chute. Ideally I'd like to be able to pre-charge some high volume capacitors from a single 9v battery and provide enough amperage that I'm sure they'll fire. A common problem we'd encounter is that the drogue would fire fine but then the battery would be too weak to provide current for the main after a couple uses.
My current idea is to use a single boost step-up dc/dc converter to step 9V to 25V and store that in a pair of 470uF Aluminum-Elec caps and then use a transistor to control discharge. I simulated this in SPICE and I get about 500ma for ~100ms which should be enough, however I was wondering if anyone knew of a better way to provide a short high current burst. Usually when we fire igniters on the ground it's from a 12v car battery or similar.
