This is a very cute hack that does something which I thought was impossible: an implementation of an FM transmitter that has exactly two components: a battery and an ATtiny45 microcontroller. It’s brilliantly obtuse and cool:
The basic idea is to trick the internal oscillator of the Atmel to run at 24Mhz. An internal PLL will run at 4x that frequency, which is a 96 Mhz signal (right in the middle of the FM broadcast band). By varying the frequency up and down, you can generate an FM modulated signal. Beyond clever. Very cool.
I was reading up on resistor ladder DAC circuits on Wikipedia, and came across the Unequal Resistor R-2R Ladder Optimizer. It’s very neat! You can enter the number of bits you need, and the values of the pile of resistors that you have measured from your bench, and it will produce an optimized design using those values. When you are making an 8 bit DAC, the normal variation in a 5% tolerance (or even a 1% tolerance) can cascade to keep you from being entirely linear, or even monotonic, so doing this optimization seems enormously practical. As a bonus, once you have your DAC simulated using the Falstad Circuit Simulator, which is itself an enormously cool thing: a Java based circuit simulator that can accept new models encoded on the URL! Paul Falstad has a huge number of other cool educational Java applets, check it out!
And indeed, he’s right! WDC (the Western Design Center) has made a new version of the 6502 available at mouser.com. It’s a 40 pin DIP package, listed at $6.95 in quantity one, and can be clocked up to 14Mhz. It sends my mind racing back to the days of Star Raiders on my Atari 400. Not sure why it would be a good part to use other than nostalgia, but I’m bookmarking for future consideration.