Upgraded Nerf Gun Keeps Track Of Your Ammo

[Paul] and his buddy [Jonathan] recently had a zombie themed Larp event to go to, so in the spirit of making the experience more realistic, they decided to upgrade their Nerf N-Strike Stryfe gun.

They started by cracking open the gun and making note of the available space for a few bells and whistles. Luckily, thanks to traditional plastic injection molding practices — there’s lots of room!

Upgrades include a magazine sensor, a jam sensor, a trigger sensor and a voltmeter to make the gun a little bit smarter. A knockoff Arduino Pro Mini takes in all these inputs and outputs it to a 7-segment LED display for easy visibility. Our favorite part is the ammo sensor, which keeps a tally of how many shots you’ve used. It’s simply an IR photo-diode and IR transistor in a Darlington configuration, connected to the GPIO interrupt pin on the fake Arduino.

It’s not an overly complex project, but very nicely executed — Maybe Nerf should adopt something like this in the future! Still waiting on an automated sentry turret though…

And if you’re curious about ZombieLarp, you can find out all about it here!

8 thoughts on “Upgraded Nerf Gun Keeps Track Of Your Ammo

  1. I wonder why that darlington configuration was needed; the phototransistor should easily be able to provide enough current to get a good signal to the I/O pin of the controller. To much gain isn’t good either; it could cause a false trigger if you happen to point the gun at a bright light source.

    I think the next upgrade should be to recognise each magazine, maybe using something as simple as a different value resistor in each magazine and 2 contact points in the gun, with either a current source or simply a second resistor and an analog input on the controller. That way, you could keep track of the number of remaining darts in each magazine, so when you only have partially used magazines left, the reading is still correct.

  2. Note: it’s not a “fake” arduino. it follows the published schematic and eagle files. it’s a “real arduino” just not the arduino sold by the official sources.

    Do you guys call Lada ADA’s and Sparkfun arduinos “fake”?

  3. I did something similar for my airsoft gun. Instead of using a light gate, I measured the battery voltage, and whenever there was a sharp dip, my uC knew that the trigger had been pulled.


    It works fairly well, but it took a while to tune the “DSP” to detect shots reliably. It still doesn’t detect 100% accurately, and doesn’t quite count right on full auto, but it’s easier to mount and install than a light gate!

    PS the LEDs are useless in daylight. v2.0 will use an LCD

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