Edit, answer: I managed to figure it out with help from passerby's answer. I needed a pull down resistor for the PNP transistor. Here's the final schematic:
When the beam of the photo interrupter is unbroken, the LEDs are off, and when you break the beam the LEDs come on.
I'm making a money checker, to check for the existence of a security strip in US bills. My project will use UV LEDs, but for the sake of brevity here I'll just call them lights.
Basically, I'd like to build a circuit, without a microcontroller, that turns on the lights when the beam from the photo interrupter is broken. My understanding of them is that the IR detector is a phototransistor which allows current to flow when exposed to IR light, and blocks it when not. Could I use the output of the phototransistor into the base of a PNP transistor to turn on the lights? Again, my understanding is that with a PNP transistor, current at the base blocks current through the connector-emitter, so I could put my lights in series with C-E of the PNP, and the base of the PNP to the C-E of the phototransistor, right? The idea is that when I place a bill in the slot of the photo interrupter, the lights will turn on, and when I remove it they'll turn off. If I've figured this right in my head I shouldn't need much more than what I've mentioned plus a few resistors, right?
I'm on a phone right now, and I don't have internet at home, so I can't make a schematic.
Edit: I'm not sure how I could make what I'm asking any clearer. I want to turn on some LEDs when the beam of a photo interrupter is broken, without using a microcontroller, all of which I stated in my original text... Here's a picture of a hand-drawn schematic...
I've calculated that with a 3.2Vf drop across the UV LEDs, and 12 in parallel (I know I messed that up in my schematic), I'd need a 5.416 ohm resistor to get 20mA each. If I up the resistance to 10 ohms, I'd get a bit over 10mA each and have 169mW dissipated in the resistor. The 180 ohm resistor is to limit the current of the 1.2Vf IR LED in the photo interrupter to a little less than 20mA. The only thing I'm unsure about is the pull up resistor.