Now here's a really fun project! We're going to get the PIC16F88 talking and listening to a TI-83 Plus calculator. If you're not familiar with this, it's a tremendously popular graphing calculator used by perhaps millions of students around the world.
By connecting it to the PIC, we get immediate access to all of its power. So, for example, you could offload some complex calculation involving transcendental functions (trig, logs, exponentials, etc.) and then read back 14-digit floating point results. Or, you can have the PIC guide the TI-83 Plus through some graphing. The uses really are endless.
Electronically, the communication protocol is a cinch: a 2.5mm plug and wires is all it takes. On the software end of things, however, it gets convoluted in a hurry. But not to worry! I've created a PMP library unit that takes care of all the messiness. Check out the code for the demo program and the unit, and see for yourself.
If you'd like to learn more about what's going on under the hood, may I point you toward an article I wrote back in 2013: "A Mathematics Engine for Microcontrollers," Nuts & Volts Magazine, August 2013, pp. 44-49. You'll note that the software for that is in the Great Cow Basic language I used prior to finding the far superior PIC Micro Pascal compiler.
And to find out more about the hundreds of commands possible, be sure to go to the horse's mouth. Romain Liévin and Tim Singer have put together a very complete guide to the TI Link Protocol that I found indispensable when writing the library unit:
Let's see the circuit:
Not much to it, is there! But beneath the surface is a complicated dance of the two wires in the TI Link Protocol. You'll find tons of handshaking going on. And since the communication is full duplex, there's also a lot of flipping the port lines from zeros to ones to the tri-state condition. But again, the library unit shields you from the ugly minutiae. So, just sit back and enjoy a new mathematics engine for your PIC.
Here's a short demo of just a few of the things you can do.
Click to get the source code.
Click to get the schematic PDF.
Next Project: Infrared Communication