wmb@sun.UUCP (Mitch Bradley) (08/31/83)
There is a technique for increasing the effective number of bits of an A/D conversion, if you can afford to have the conversion take longer. The trick is to superimpose a triangle wave or sawtooth wave on the voltage you are sampling. The waveform should have a period which is some multiple of the sampling period of the A/D (hopefully synchronized with it), and an amplitude of 1 step size peak-peak. Then you take several samples, where several is the number of sample periods in one period of the waveform (for a sawtooth wave; for a triangle wave, several is the number of sample period in one half-period of the waveform). Then you add all the samples up to get a number which has more bits in it. For instance, if you take 1 6-bit sample every 1 millisecond, and you have a sawtooth wave with a period of 4 milliseconds, then you can take four samples every 4 milliseconds to get an 8 bit conversion every 4 milliseconds. I will leave it as an exercise for the reader to figure out why this works, because I can't think of an explanation that I can write down in the time I'm willing to spend on this. Anyway, implementing this could probably be done with a 555 and a few resistors and capacitors. I'm not going to do it because I don't have a CoCo. Cheers, Mitch Bradley Sun Microsystems, Inc.