Bruce Bowling wrote:

> Design criterion: simple and cheap over accuracy.
> My entry to your "contest" is 2 resistors and a beat up cap

If the pulse is constant height (ie output from a gate would do) I
would use two resistors and a capacitor and two port bits one as an
output and the second as a sense input. I would turn the processor
into a high gain "op amp" and do statistics on the number of ones
fed back. The system works as a current summer with the Cap whose
value is non critical being a low pass filter. The energy in the
pulse can easily be measured and since we know the value of Ri,Rf
and the pulse height we can easily calculate its width. Should be
good to about 10 bits or so.

The added advantage is that it will measure asyncronous pulses.

                                  Rf     |
                            ---- \/\/ ---| Port bit out
                 Ri        |             |
Pulse In ----- \/\/\ ------|             |
                           |             |
                           |-------------| Port bit in
                           |             |
                Cap       ===            |
                           |
                          ---
                           -

I have used similar systems for very low cost A/D systems where I can
trade time for accuracy. 10..12 bits are possible with only two critcal
resistors.

Walter Banks
Byte Craft Limited
(519) 888-6911
walter@bytecraft.com

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