I was digging around in a thrift store and found an old tax calculator. I want to see if I can hook it up to one of my Raspberry Pi's or something, but what it's connected to doesn't really matter because I want the connection between the calculator and whatever controls it to be decoupled. My end goal is to have some sort of interface to the calculator so I can send an alphanumerical character to it and have it print it out (including newlines).

Since I'm only 16 and haven't had much experience with devices such as this and situations where I repurpose a machine, I made an account on here to see if I could get some help. Honestly, I'll need a bit of help to understand how I would do this, due to my previously stated "beginner's status". I've had a lot of experience with programming, but I don't really think that will be a big problem for the interface; however, programming will be important in the controlling later on. But don't worry about that. I have a bit of knowledge about circuit boards and their components, as well as the principles of electricity, but not enough to understand a machine such as a tax calculator.

I know I probably sound like I have no idea what I'm talking about (which is probably true), but I have two ideas for the methods of patching into the device.

• The first method would be manually controlling the individual motors of the printer with the interface, which means the interface would have to have some sort of software programmed into it and an ability to send different voltages and possibly frequencies(?) to the motors.
• The second method would be somehow patching into the calculator's brain and making it think there were alphanumerical characters needing to be written. I'm not sure if this thing has a buffer of some sort for the physical text output, but something along those lines would hopefully work.

I'm going on the assumption that you all can pull up blueprints for this machine somewhere, but if you need any sort of pictures I can provide them.

 

The problem I foresee is that the printer probably lacks any kind of standard interface. I also think you underestimate the availability of schematic diagrams of the internal connections. Since there is relatively little need for schematic diagrams unless the units are going to be repaired and the last electronic repair shops closed decades ago. I suggest you try to find the documentation you think exists just for grins.