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In my never ending quest to turn garbage into something useful, I designed a circuit that will input 8 bits into the Odyssey 2 without affecting any other lines on the bus. Really, you are either on the bus, or off the bus, but in this case I simply try not to interfere... My circuit goes further than any other Odyssey 2 cartridge, even if it does create a weird load. I think, though, that the power supply and bus of the stock Odyssey 2 can handle this just fine. One time in Eugene I got off of the bus (literally), and I was quite angry about something or other... worries... horror. Anyway, I walked next to this guy in an aviator cap. I believed it was Kesey. All of a sudden, all of my thoughts went blank... I was no longer in turmoil. The guy in the aviator cap smiled, as though he had done this to me. I walked to the pie shop as I had many times before. I was still experiencing the emptiness in my head after Kesey sucked out all of my thoughts... I glanced down at a manhole cover, and it read "Illumination". I never had noticed that manhole cover before. Anyway, in this article I showed how to load up a binary file that had 0x01 everywhere except 0x02 at location FF. I burned this into a 2716, and I have a poor man's PAL. This simply disables the main EPROM at FF, and puts the data on the 74LS244 on the bus. Now, you might think that this is a pretty heavy chip to be using in this circuit. The thing is, though, that there are a bazillion of these that are 25 years old or so that have never been erased and were bumping around plugged in to sockets on boards. Most other chips are soldered on to the board and are harder to recover; however, EPROMs are unique in that they are almost always in sockets. It is quite easy to pick these up at auction for 50 cents each. I also raise D0 and D1 high with a 1K resistor. This helps stabalize the circuit, since the O2 uses OE to disable the EPROM. I could have switched to CS, but I use that on the main program EPROM to disable it.
It is easy to expand this to up to 56 input lines by using D2-D7 for CS on additional 74ls244 chips and mapping another 6 I/O addresses.
Here is the circuit:
Click for larger image
Here is a picture of the breadboarded project:
Notice how I used the extender card from "The Voice" module to bring the bus out to the breadboard. Here is the fig file. I wrote up a program to monitor voltages on my PV system here.
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