I am currently working on what I call a High Voltage Sparker which is based on the same basic principle as a Tesla coil. It is basically made of 3 transistors, 2 old TV flybacks a bunch of capacitors and a spark plug. It can generate sparks aout 5 cm long. If that's two much, you can remove the second flyback. If you're interested I could post a schematic.
I am currently working on what I call a High Voltage Sparker which is based on the same basic principle as a Tesla coil. It is basically made of 3 transistors, 2 old TV flybacks a bunch of capacitors and a spark plug. It can generate sparks aout 5 cm long. If that's two much, you can remove the second flyback. If you're interested I could post a schematic.
That sounds interesting but might be a little overkill. I made a spud gun before with a 4 foot long 2" PVC barrel that launched potatoes several hundred feet at least. I used hair spray as the fuel and a BBQ igniter to fire the thing. It is a low cost and readily available solution that doesn't require power or messing with potentially dangerous high voltages. IMHO.
I would suggest using a simple CDI ignition as is used in model airplanes and boats. This link is a DIY version. This is a forum devoted to that version. You do not need a microcontroller to just get sparks.
In case you are adventuresome, here are reverse engineered circuits from a Chinese (left) and American (right) commercial CDI units.
Most people stumble on making the transformer. For single sparks as one would use in a spud gun, a transformer from an electronic flyswatter, CCFL, or similar will work. You will not need the hall switch. A simple push button will work. Finally, be aware that all of these circuits may give a spark when first turned on. be sure, therefore, to have the circuit turned on before loading your spud gun, or you may get a surprise.
John
Edit: Ignore the thumbnails. They somehow got inserted and I can't delete them.