Calculator Hijacking

I’m making something that requires remote control of a printing calculator. I’ve got it working.

You’ll be able to find out more about what I’m doing with this in my sculpture portfolio (to be updated in the next week or so with some of this new work). In the meantime, here are a few photos describing how this thing works.

The setup, in generalIn this photo, I’m typing one-letter commands into a terminal emulator on the MacBook. For example, if I want to pretend that I pressed the number 1 on the calculator, I can type ‘1’ on the MacBook instead and it’ll appear on the calculator. That really sums up this whole thing, for the most part.

The serial interfaceThe MacBook is able to communicate with the circuit board that I created and placed in the calculator through this thing. It matches up the hardware in a computer’s serial port to the serial capabilities of the microcontroller that I’ve hidden in the calculator. I love how this thing looks – once I made it I needed a small case so I used the shell of a broken pressure gauge that I had lying around.

The brains of the operationThis is the meat in the sandwich. This is the circuit that I created to actually do the hijacking of the calculator’s keyboard and pretend to press buttons (it’s the board near the bottom with all the wires attached to it). The microcontroller (the big chip-looking thing way at the bottom) is what communicates with the computer (the MacBook in this case) and simulates a keypress on the calculator. It does that using optoisolators, which are the eight smaller chip-looking things you can see in the photo.

I designed the board with pin headers everywhere so I can re-program the microcontroller without removing it from the circuitboard (in case I screwed up and there’s a bug in the software I wrote and burned onto it). There are also a couple LED indicators on the board, to show when the board has power and when it’s receiving something from the computer. The round bit that you can barely see on the right is a piezo disc that I put there to make a clicking noise when each button is “pressed.” There are also commands that you can send from the computer to just making clicking noises inside the calculator.

The hijacked calculator This is the whole thing. When I’m done, it’ll look like a calculator again and instead of communicating with my MacBook, it will get its commands from a hidden Linux computer that gets the data that I’m tracking from RSS feeds on the Internet.

That’s all the nerd stuff, but it will be a lot less about the technology and more about the concept once it’s finished and installed properly. Keep an eye on the portfolio this month.