The Open 7400 Competition is over and the winner is…. Capacitive Sensing, the Hard Way! This is a project that is somewhat simple when done with a microcontroller but takes quite a bit of effort to pull off with 7400 chips. I think the winners are still trying to determine who wants what since I haven’t heard who is going to be awarded the three IR Jammer kits yet.
“The capacitive inputs are selected using 74xx-ized analog switches (‘4051). The channels are selected using a synchronous ‘161 counter to feed a RC-oscillator build around a couple of ‘132 Schmitt-trigger nand-gates. The channel counter can be put on hold using the DTR signal from the RS232 port. The counter is automatically advanced by the channel sequencer (if DTR enabled) after the measurement period. There is of course a 16-to-1 analog multiplexer available, but it comes in a 24-pin package and that is monster size compared to the 16-pin package of the ‘4051. Besides, we need at least one inverting Schmitt-trigger gate and the options are 6- or 4-in-a-package. No reason to let the gates go unused. The design, as is, uses one extra analog switch package, but still saves space on the board.”
There sure was a great number of entries to the contest, you can browse through the list of all the entries below.
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