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I Hacked the NES Zapper to Win Duck Hunt Every Time
2025-07-13 | By Zach Hipps
License: See Original Project Microcontrollers
Do you remember when I built those giant boxing robots last year? My friend Will came over, and we had a "friendly" little competition. Well, he absolutely mopped the floor with me. I tried to be a good sport, but honestly, a little part of me has been plotting revenge ever since. So, I’ve been scheming, and I’ve decided to invite Will back for a rematch! We’re going to play the classic Nintendo game, Duck Hunt. You know, the one where you use the Zapper to shoot down ducks, and that infuriating dog laughs at you when you miss? Yeah, that one, but I’m not leaving this to chance. I have a plan that will guarantee I win every single time.
First things first, I needed to understand how the Nintendo Zapper works. My theory was that there was some type of photodiode inside that detected color, and when you pulled the trigger, it told the console whether it was a hit or a miss. To confirm this, I had to crack it open. After carefully removing the screws (and finding a sneaky hidden one!), I got a good look inside. Most of the electronics are positioned in the center, and a heavy weight is added to make the Zapper feel more substantial. The key component appears to be the photodetector, nestled inside a small metal hood. To truly understand what signals were being sent between the Zapper and the console, I grabbed my logic analyzer. Instead of cutting up my vintage Zapper, I ordered an extension cable that will go in between them in series; it's much better to chop up a cheap cable than a piece of Nintendo history!
With the extension cable connected, I fired up the logic analyzer software. I was particularly interested in pins five and six, which I suspected handled the trigger and color information. I made some test hits and some test misses with the Zapper. I took a look at what the software had captured, and what I saw was fascinating. The trigger signal starts high, pulls low when the trigger is pulled, and returns to high on release. Simple enough. Then there was the color data, which was a constant pulse, but with a noticeable gap after the trigger pull. Perhaps this is related to whether I hit a duck on the screen. I then measured the gaps. For a hit, the gap was about 33 milliseconds. For a miss, it stretched to 66 milliseconds. It looked like we were onto something. I also noticed the color data pulses were at 60Hz, which is the same frequency as North American wall outlets. This suggested it might be related to the screen’s refresh rate. I started a new logic session and just aimed the Zapper at the screen. Lo and behold, I got that beautiful 60Hz pulse. When I pointed it away from the screen, I got nothing. This confirmed the Zapper was indeed "seeing" the screen. Then came the real breakthrough, thanks to some slow-motion analysis of the game footage. After the trigger pull, the screen goes black for one frame. Then, a white square briefly appears exactly where the duck was for one frame. Finally, the next frame starts drawing the duck. This was it! If the Zapper's sensor saw color (i.e., the white square), it was a hit. If not, it was a miss. The different gap lengths made perfect sense: a miss had two black frames back-to-back because the Zapper wasn’t aimed at the white square on the second frame, making the "no color" period longer. I cracked it!
Now, I want to replicate this. My plan was to disconnect the Zapper and use a microcontroller to inject my own signals directly into the console. Here’s the basic idea… I set the trigger pin high, sent a few color pulses, then delayed for a single frame (simulating that one black frame with no color data). After that, I toggled the color pin again for another 50 cycles, tricking the console into thinking it saw the white square. Finally, I’d write the trigger pin low. I carefully chose these values so this sequence would loop, essentially "pulling the trigger" and registering a hit every second. I unplugged the Zapper entirely and connected my microcontroller. The moment I loaded the code and unpaused the game, it was glorious: DUCKS WERE DROPPING LIKE FLIES! They barely even cleared the horizon. My engineering skills were simply too much for those pixelated birds. Should I feel bad? Nah, I don't think so.
Next, I updated the code to trigger a hit only when a button was pressed. This would allow me to control the "hits" manually. And just like that, every single button press was a guaranteed duck elimination. Take that, annoying dog! You're not laughing now, are you, punk?
Now that I knew I could generate the right signals to trick the console, it was time to put the microcontroller inside the Zapper. The idea was for the microcontroller to sit between the Zapper's internal module (the photodiode and trigger) and the NES console. In normal operation, it would just mirror the signals through. But in "cheat mode," it would intercept them and inject my own, guaranteeing a hit.
However, there were a couple of hurdles—first, the signal’s integrity. I needed to ensure the microcontroller could read and pass through the normal Zapper signals perfectly; otherwise, the game would detect something was amiss. Lastly, I had to fit all these new parts inside the Zapper. Even with a small microcontroller, there were a lot of wires.
Then, I got stuck for days on a new problem... Remember that nice 60Hz pulse I saw when the Zapper was connected and pointed at the screen? When I tried to read it with the microcontroller added inside the Zapper, it was no longer there. I was pulling my hair out! Then it hit me, when the Zapper is connected to the console, the input is held high, meaning there's a pull-up resistor inside the console. The internal pull-up resistors of my microcontroller were simply too weak. A quick check with my multimeter confirmed the console was using a 10K resistor. After I soldered an external 10K resistor between the 5V pin and the color pin on my microcontroller, the beautiful 60Hz pulse reappeared, and I was immensely relieved.
To make my Zapper even more devious, I utilized the microcontroller's handy RGB LED and a Hall-effect sensor. It glows green in normal mode and turns red when I activate "cheat mode." My secret weapon was a small neodymium magnet hidden behind my wedding ring, which triggers the Hall-effect sensor inside the Zapper. When I hold my ring close, the LED turns red, and I become invincible!
With everything ready, it was time to call Will. I got him on the phone, and he was game for a Duck Hunt match! Little did he know what was in store for him. I even superglued the magnet into my wedding ring right before he arrived, just to make sure it was perfect. When Will showed up, we got started. I let him go first. To my feigned surprise, he was terrible. Missing shot after shot, with that dog incessantly laughing at him. He hit only one out of ten ducks.
Then it was my turn. I activated cheat mode with my subtle ring maneuver, took aim (at least pretended to), and every single shot was a hit! I scored a perfect ten, earning a high score of 19,000 points. Will was baffled, trying to figure out my "technique." I lied and told him I'd been practicing and that there was something about the duck's "flapping" that told me where it was going. I even hit ducks with my eyes closed!
We played a few more rounds, and the results were consistently lopsided. I even let him stand as close as he wanted to the screen, while I shot over my shoulder without looking. Still, he struggled, while I was a showboat and got perfect scores.
Eventually, suspicion of cheating dawned on Will. "The thought occurred to me, like, honestly, kind of embarrassingly late," he admitted, "like maybe about halfway through the second round, I was like, wait a second."
It was time for the big reveal. "I have to admit something," I confessed, "I may have used a little bit of 'revengineering' to guarantee that I won that game." I showed him the Zapper's LED, which turned red when I held my hand over it and green when he took it. "I actually hacked the Zapper," I revealed. "I put my own electronics inside there," I explained that my microcontroller was reading the signals from the Zapper's light sensor and sending back information to the console based on who was holding it. For him, I had configured it so that two out of every three shots were guaranteed to be misses, no matter how perfectly he aimed. It was impossible for him to win. But for me, with my magnet-activated invincible mode, I simply couldn't miss. Will's reaction was priceless: "I'm having these flashbacks of being like the youngest child in my family and like, just being like, that's not fair! That's not fair!"
We then opened up the Zapper together. I showed him how I cut the original cable and inserted my microcontroller, effectively acting as an intermediary between the Zapper's sensor and the NES console. It reads the sensor data, then decides whether to pass it through normally or inject my "hit" signals. "Is there a mode that is just like normal?" Will asked. "No," I admitted, "I kind of got really evil at the end, and I was like, okay, I need to add it so it's only one out of three shots."
Thanks again, Will, for coming over and being such a good sport! You’re welcome back anytime, though maybe next time we'll stick to Rock 'Em Sock 'Em Robots. A huge shout-out to my friend and Patreon member, Andrew Howard, for this brilliant idea! We had so much fun discussing this project on the Byte Sized Engineering Discord server.
Hong Kong, China