I built this Nerf Sentry Gun by grafting a couple of Arduinos, a power supply, a motor, and an ultrasonic distance sensor onto a Nerf Vulcan machine gun. I posted these build notes on Make: online. I’ve never compiled them all in one place, however, so this post serves to tie the whole project together in one place.
Part 1: Wiring the trigger
The first step was to add wiring and a two-wire connector to control the trigger circuit. I opened up the Nerf Vulcan (about 30 screws) and soldered an 1/8″ female jack to the fire selection mode switch. This way, I can retain all the regular functions of the gun when it’s unplugged from the Arduino. To control it from the Arduino, I’ll flip the orange switch on top to “off” and then wire the trigger into the “pulled” position (done here with a classy twist tie). Whenever the Arduino’s trigger circuit closes (bypassing that orange “off” switch) the gun will start firing.
To add the connector, I drilled a 1/4″ hole in the gun’s hand grip, fed the sleeve through, and secured it with a couple of zip ties inside for strain relief.
Next, I’m planning to build the Arduino’s trigger circuit using a MOSFET transistor wired to a male 1/8″ jack I can plug into the gun.