Potato Gun Ignition Spark Controller

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davidnorman
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Potato Gun Ignition Spark Controller

Postby davidnorman » Sun Mar 20, 2011 12:44 pm

Version: 0.1
Status: Just an idea
License: BSD
Download: https://github.com/DavidNorman/XC-1-Potato-Cannon

The digital supervisor for a high current spark generator used for ignition fuel in the combustion chamber of a potato cannon. The main spark circuitry is based on a camera flash circuit. A FET H-bridge provides low voltage AC across a current transformer which steps 9V up to 300V. A big camera flash Cap is charged, as is a smaller Cap for the trigger. Once charged, a separate trigger fires a triac, releasing the trigger current through another current transformer to get 1.5kV, enough to ionize the air between the spark gap. Once ionized, the large 300V cap discharges across the spark gap, creating a high-current arc, enough to efficiently ignite a chamber of fuel (Tesco's value brand hair spray - which is basically a light butane/propane mix with some glue disolved in it).


Will be adding a countdown timer with 2 button up/down control, and an external dual 7-seg LED block with some shift registers to show the countdown.


Images:
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davidnorman
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Postby davidnorman » Thu Mar 24, 2011 9:53 am

Since the shift registers for the LEDs are 5V, and they don't accept 3.3 as a logic input level, I used the pull-up version of the output port driver, and some external pull-up restistors. Thanks Corin for pointing out that the ports have this feature, and thanks trusty 'Programming XC on XMOS Devices' for providing the name of the XC library call.


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davidnorman
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Postby davidnorman » Thu Mar 31, 2011 1:56 pm

Assembled the capacitor charging prototype circuit. Picture uploaded. Will tune the charging to make sure that it doesn't overcharge. The current transformer was scavenged from a disposable camera, which works at 1.5V, so the 5V USB power source will overcharge the capacitor. I am hoping that I can use the inductance of the transformer, with suitably short charging pulses, to limit the voltage into the transformer, and therefore tune the voltage using the charge pulse period.
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davidnorman
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Postby davidnorman » Sun Apr 03, 2011 8:32 pm

I've implemented the charging code and checked into github. It takes about 10 seconds to put 250v into the main cap. You can get a pretty mean spark from that. I've played with a trigger circuit but no joy yet. May have inadvertently broken the trigger transformer while removing from the other flash circuit. Debugging progresses...

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davidnorman
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Postby davidnorman » Thu Apr 07, 2011 7:44 pm

Now have a manual trigger for sparks. Not long until an electronic one exists. Think I am going to have to optoisolate the XMOS board, since there is considerable voltage spikes going into the board, and occasionally it causes it to lock up.
m145mcc
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Postby m145mcc » Fri May 06, 2011 10:36 am

I was doing some recon and came across your blog, do you have a wiring diagram or schematic I could take a look at? its a very neat concept, I was trying to do something smiler a few months back.
tommike
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