Switching Circuit

In this Instructable (my first) I have posted the circuit design that I am currently fiddling with for its eventual use in my coilgun. When it is finished it will serve as the activation switch for a second coil. Like I said; I am still modifying the circuit and I'm currently looking for a bit of advice, so any ideas would be helpful.

Continue on to the next page for a few more details.

Step 1: The Parts

Of course with any electronics project you have to have a parts list. Here it is so far.

3904NPN Transistor
3906PNP Transistor
Diode (not needed)
LDR (Highest Ohm rating I could find @ radioshack)
3-16V Buzzer

The buzzer is on the circuit in place of the relay that will eventually be used to short out my capacitor bank.

Step 2: Schematic

The idea of my circuit consists of an LED, LDR, relay, and a digital switch. when put togeather the LED and LDR will be placed on opposite sides of my coilguns barrel and the digital switch will turn ON and stay on when the projectile passes between the light and the light detector. My current problem (current...lol) is that the switch does just the opposite. When the light is introduced, the circuit is turned OFF and stays off.

Step 3:

Basically what this Instructable is an attempt to do is create an SCR without having to buy one through some online electronics superstore. I'm so close, but I'm definitely stumped at this point. If I have left out any info that would help you help me, feel free to message me. Ill be back with an answer ASAP.