Pulses to proportional voltage

Do a web search for "speedometer circuit". You can increase the frequency with more magnets (say use one every 90 degrees).

There are sensors that'll work off of the sprocket on the motor, if it's ferrous. Web search for "gear tooth sensor" or similar. That'll give you _lots_ more pulses/mile.

martin

Ok, I'll look into a gear tooth sensor and the LM2907. Thanks, Mike

if you don't mind the needle being a little sluggish it can be done. more pulses is better. can you get at a cog wheel or something? possibly put a variable-reluctance sensor near the diff's crown or pinion wheel?

no. all you need is a 555 one-shot and a few resistors and capacitors.

Bye. Jasen

From this alone, i suggest you count the time between successive pulses and do a divide. That is what i did when faced with a similar problem. Ought to be serious overkill. I once had a SYM-1 SBC doing much more, like 4 interrupts per revolution at 700 rpm and doing process monitoring as well, control keyboard, and live 20 character 7 segment display with a 1 MHz 6502; could display total turns, 4 channels peak forces, operating speed, current time or date, and start/stop the machine. With the machine stopped you could set speed limit values, force limit values, force imbalance limit values, automatic stop turns counts, automatic stop time and date, rtc time and date; and of course it would auto stop on any out of limit conditions and switch the display mode and show the out of limit condition.

Why not a simple charge-pump-style _analog_ speedometer?

...Jim Thompson

Hmmm. Because they are notoriously flaky at those low pulse rates?

Isn't this the same gizmo which has a sprocket wheel ?:-)

...Jim Thompson

IIRC from upthread this is one pulse per turn of the roadway wheel. Design changes to use a sprocket wheel sensor involve mechanical reconfiguration as well. OP may not be interested. Besides the 1/t system proposed works fine.