What was always bugging me about my TI was that I couldn't interface it with the real world. To change that, I created the TI92+ PIC Extension board. The TI enslaves a PIC18F microcontroller using its serial Link Interface. Basic operations are peek(addr) and poke(addr, value). There are some more macros for getting adc values or getting timestamps.

I have documented my current progress on my homepage. The current prototype is on a perf board and lacks some planned features (UART/SPI buffers, USB socket, 3.3V/2.0V power supply), but is generally operational. I also posted some examples.

If anyone has any ideas on how this project could be improved, I of course welcome any suggestions

Edit:
Despite of my best efforts my camera is refusing to produce decent pictures of the perf board, so I guess I'm stuck with presenting the low-res screenshots from my site.

Here's a picture of the current design state inside its altoids-like housing:


And here's a link to a short AVI showing the usage of TI-controlled PWM modulation to create a breathing light, followed by setting some digital values (7,3,1,0) on the digital output port: http://core-vector.net/files/TI92_ExtBoard_Example6.avi

Yay hardware hacks! Looks really awesome. Kind of like a TI-92 Arduino, right?

@pimathbrainiac: Yes, in that the TI92 becomes sort of an Arduino (using a MicroChip PIC18 instead of an Atmel ATMega) with a keyboard, basic interpreter and screen built in ^^

The project does have some similarities to the ArTICL (http://www.cemetech.net/forum/viewtopic.php?t=10809) in that the TI is linked to a microcontroller. However my focus here is to make the microcontroller's features accessible to the TI (as in using the ADC, digital Ports, DAC...), while ArTICL is as far as I can tell a generic link library for the serial port.

I also wanted the design to be standalone; sort of an analog extension kit. What you do with solely depends on the TI and the basic scripts, you don't need to reprogram the microcontroller "in the field".

Some useful examples of how this project helped me (as an example for some use cases):

Life power metering of solar cells. Using two ADC channels, a 1kOhm resistor and a 1 Ohm resistor, the TI could measure the power generated by a cheap solar cell (one of those garden-lights-things). That helped to conclusively settle an argument concerning if these chinese things could ever recharge a NiMh accumulator to a sufficient degree to keep an LED operating for more than 2h/night (the answer is "No").

Measuring capacitance. Discharging the cap over a pin, then using the precision current source of the PIC to charge it and measuring the result using the ADC allowed me to determine the capacitance of some larger (nF) caps lying around.

Figuring out the command encodings of a very sparsely documented alphanumeric display... by brute force. The display was connected to the GPIOs of the PIC and a TI Basic script allowed me to send commands and monitor the results.