Motion Timer

Nov 15, 2004 3 Replies
L

I am looking for some guidance in designing a timer circuit. I have a pneumatic cylinder that has 2 hall effect switches, one at either end of the stroke. What I need to do is measure the time it takes the piston to travel between the 2 switches and then display the time, preferably on an lcd display. It has to be capable of timing the piston in both directions and preferably autoreset the display when the direction is reversed. The total time will be ~2 sec and I'm looking for ~1/1000 accuracy.



It's been about 10 years since I've done any electronics design so I'm looking for a little help getting started with this project. Can someone please suggest a direction to take with this project and suggest some components to consider.



Thank you.


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C

Perhaps a standard counter/timer would do the job...

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..plus some switches to swap the start and stop inputs over to measure the reverse direction. If you use something like a rotary wafer switch it should be possible to hook it up to momentarily trigger a reset when changing over. (eg use a three position switch - Forward, Reset, Reverse)

Do you need the display to reset and remeasure on each stroke or just one stroke after changing direction? If you want a continiously updated display you may need a buffered display and/or play around with the gate input.

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J

If you want to do it brute-force in hardware, you'll need five decade counters, five BCD to seven-segment LCD decoder-drivers, a suitable clock oscillator, a five digit static LCD display (reflective or transflective if you want to use it with ambient light or transflective if you want to use it with ambient light or a backlight), some glue logic to latch the accumulated time of the current stroke into the display and reset the counter to time the cylinder's next stroke, and maybe a couple of comparators to crispen up the outputs from the Hall sensors. If you want a schematic, ask and I'll draw one up for you and post it to alt.binaries.schematics.electronic.
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J

Oops... X.XXX seconds = 4 counters, etc.

John Fields
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