Comment by nom | Hacker News Reader

Comment by nom | Hacker News Reader

A bit OT but this just reminded me of something I haven't thought about for many many years. Just wanted to share.

I bypassed the payment procedure in a coke vending machine with a lighter.

Germany, around 2004 we had a coke vending machine at school, probably from the mid 90s. Someone told me you get free coke if you flick a (non-piezo) lighter in front of the display at the right time. I didn't believe it one bit, but when I tried it, it actually worked. It quickly spread around our school until months later the service guy fixed it.

Many years later I realized what has happened. The flick of the lighter emitted a strong IR impulse that triggered an infrared receiver (which was probably used for debugging, configuring etc).

This must have caused an interrupt, and if triggered at the same time the machine vended the bottle, it completed vending but never got back to actually decrementing the money you put into it. You could empty out the whole machine with nothing else but 1 Euro and a lighter and you even got your money back.

Lots of cokes were had.

When my sister lost the "sensor bar" on her Wii I showed her how to use a pair of candles to replace it. The sensor bar is just a a set of IR lights that the camera on the wii-mote detects.

I'd imagine a pair of candles would cause the cursor to jump around a lot because of the flickering - how did you solve that problem?

With a clean, dry wick it's pretty easy to get a very still flame for a long, long period of time. Though if you have a fan or something blowing, you're out of luck.

I imagine a vigorous game of Wii Tennis will cause those candles to flicker.

And will provide a convenient excuse why I was unable to return that serve.

Unfortunately your excuse is no good, because Tennis does not use the Sensor Bar.

Well then that's my excuse! I thought it did, so I was making sure to point the controller in the proper direction, while my opponent was cheating and flicking it any which way.

Look, it wasn't my fault, ok?

Use a candleholder that includes a glass sheath. The solution has been known for a long, long time, because a major cause of flickering unprotected candles -- or even extinguishing them -- is that you walk around while holding them.

Miniature lightbulbs works to the same effect. Anything that emit near IR works.

Yeah it's funny that it is called a sensor bar when it has no sensors.

For my undergrad, we had a cross-major project to build a robot that shot pingpong balls at various targets that were tagged with IR lights. We used 2 wiimotes to calculate the 3D space.

Valve lighthouse "trackers" work in a similar, albeit slightly more complicated, way.

Yes! I am now imagining a vive tracker built out of two candles spinning at 300hz

What could go wrong!?

Yeah I did that one time as well! I had forgotten the sensor bar at someone's place after taking the Wii there.. had it back and home and remembered it's just IR LEDs or whatever, figured two candles should emit the ~same light and, lo and behold, worked quite well! IIRC it was a bit jittery due to the candle flames wavering about, but hey, better than nothing :)

I have a similar experience. 20 years ago a friend told me a trick which only worked on vending machines from a particular brand. It only worked on the drinks with the lowest price. You had to put the exact money in the machine for a certain drink, add one cent and press the button for that drink right when you hear the "click" of the money. You get the drink and your money was increased by one cent. After you were done you could just get the money back. It required some practice but when your timing was good you could empty a complete machine. Since most of the vending machines had redbull and jupiler, which had the highest price, we had alot of free cola/sprite/.... I wonder if it still works.

One of the very first things I did in ~1994 with my brand new 2 meter radio was discover that it would make the vending machine in my high school think a dollar had been inserted.

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