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Well, it depends on a lot of things - there are about 3-4
different basic schemes for producing an RPM reading from a signal source
ranging from a simple pulse intergration circuit which basically charges a
capacitor to a different voltage level depending on the average voltage produced
by the pulse train all the way to a microchip based on which measure the
interval between each pulse and gives you an (almost) instantaneous rpm
reading.
Then the manner of display comes into play - a simple
cheap voltage meter could be used to display the charge on the capacitor and you
calibrate it for rpm - or there is a relative simple LED BAR graph that displays
the number of dots depending on rpm, to and LCD type read out, etc.
You could probably find something on the internet - it
would just need to handle 6 pulse/rev and whatever voltage the MT signal
is. A suitable 6 pulse/rev might be a bit harder to find than the more
common 1 -4 Pulse/rev , but they are probably out there.
Ed
Sent: Sunday, December 19, 2010 5:12 PM
Subject: [FlyRotary] Cheap prop tach
Ed,
The MT electric prop has a prop
speed pickup that senses 6 bolt heads per revolution as they go by the
sensor. How difficult/expensive would it be to fabricate an LED readout
that will give prop rpm that taps into this signal
line?
Bill
B
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