variable photoresistor to control on/off switch?

[jerryk]

Hi All,
I'm working with my son on a project to learn some electronics.
Our goal is: Light-activated nerf gun.
He wants to harmlessly zap his brothers if they open the door to his darkened room.

I've soldered jumpers that bypass the trigger (9v) switch. The gun now fires when I touch the jumpers together.

I have a photoresistor from our snap circuits. (and a big snap circuit set, but I just don't trust the 9v with the transistors I have -I've already broken my NPN, down to the PNP)

So I'm thinking the little 5v photoresistor might be able to feed the collector of a custom-bought transistor, and feed 9v to the switch circuit. ...but can a collector deal with a variable current?. (and I'm not sure how to spec/find/buy a transistor that can channel the 9v with a 0-5v variable collector current.

Or maybe I should stack 2 transistors? I've seen this.

Or would a relay do this job better?


Many thanks for any advice you might have!

-Jerry (& jonathan)

 

[KeepItSimpleStupid]

What a pain.

The problem is you know almost nothing about what you need. All I know is it uses a 9V power source.

9V is great except 9V relays don't really exist.

In reality, I would ask you to measure open circuit voltage, short circuit current and find the direction of current flow. Bear in mind, that inserting a meter will alter the actual numbers, so knowing the internal resistance of the ammeter and/or voltage burden would help too.

You would also need to find out if one of the wires to the switch is ground or 9V or something in between.

All of this information would help. So would the actual datasheet for what your trying to use as a trigger.