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I added blinkenlights to the address pins of the z80 in a TI-83 calc. LEDs add a nice touch to anything, especially calculators. There are plans for a TI-83+SE version of this which doesn't require drilling holes in the case.

Exterior of the calculator:

Inside of the calculator:

full view
There is a slide switch connected to a resistor which controls an underclock. if the switch is off, it's impossible to see the lights blinking, which is boring, however with the switch on it's impossible to use the calc.
Nice. Smile You might be able to connect an external power source, which could be pretty neat.
Ooh, I want to see a video. Smile
Looks cool! But... are you saying if the lights are on you can't use the calculator?
Update: I was trying to fix bit 3 which was stuck on and bricked the calc. I have some more motherboards, one of which will be swapped in shortly.
Update 2: I broke yet another motherboard (not sure how that happened, but that means I have an extra screen now) and I have it working again.
Here I was all excited that you got the text-based Star wars thingy working.
But this looks even cooler!
CalebHansberry wrote:
Looks cool! But... are you saying if the lights are on you can't use the calculator?

No, you can use the calculator while the lights are on, however they will blink too fast to be visibly blinking and look solid. If you flip the underclock switch, the calculator becomes unusable but the lights blink.
Video is coming here.

The first few frames are at the full 6 mhz, then I flipped the underclock switch so you can see the flashing lights.
The program is just a 16k nop slide with a jump at the end which jumps to the beginning. There is no way to exit the loop and interrupts are disabled.

I'm pretty sure that there are some oddities in the lower 7 bits because of the refresh register which the z80 puts on bits 0-7 of the address bus during the second half of the instruction fetch cycle.
That's pretty cool. I can see the binary counting sequence (sequential address instruction fetches for the NOPs, right?).

Sounds like a good learning experience, especially for understanding how the processor works on an electrical level.

You know, come to think of it, they did something similar on this show made back in the 90s, connecting LEDs to a microprocessor chip: https://www.youtube.com/watch?v=nN9wNvEnn-Q
(Secret Life of Machines was an awesome series, by the way.)
This is a really cool project. How low are you underclocking it? Could you write some kind of interactive demo that would actually be usable at whatever rate that might be, even if the OS interactions are too slow to be usable?
It's overclocked to somewhere within an order of magnitude of 1khz. I could probably go down to about 1hz if I added a capacitor in addition to the resistor I'm currently using. I'll get a more precise frequency later today. I think an interactive demo would be really cool, and I'll write something. I think a state machine with the code spread around memory would look pretty cool. The OS is certainly too slow to be usable at anywhere near these speeds.
Although I didn't get a chance to post in this topic yet, I have been watching its progress, and I am suitably impressed by your work, Hooloovoo. What inspired you to create this project? Have you considered using something like an IDE cable between your board and the LEDs to make that wiring a bit neater?
The inspiration was the blinkenlights entry in the jargon file. I'm not really sure how I got there, but it sounded cool. Since the first motherboard died (still not really sure what caused that), I added 2 byte-wide sections of an IDE cable between the CPU and the circuit board, which cleaned it up significantly. I didn't clean up the connection between the board and the LEDs because it was working fine and was already connected.
I must say, through some unexpected meeting, that this calculator looks amazing in person!
  
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