I was flying an RV6 recently with an EFIS and the RPM was displayed
on the EFIS LCD with tiny numbers about 1/8th of an inch high. No other
tach on the instruments panel. To make matters worse there
was a long delay  between the time you adjusted the RPM and the change
took place on the display.

There are two ways to measure RPM. One way is to measure
the time for one revolution and then have the computer divide
that number into a constant. Lets say it took one second to rotate once.
That is 60 RPM of course. If it took .5 second to rotate
once it is 120 RPM. So fourth and so on. Computers are busy
little beast doing a lot of other things so time is of the essence.
It takes a very powerful computer with floating point math
to do the divide quickly.

Another way is take the pulse from the CAS and up count a decade counter
every rev. Then take a look at the count once a minute, display
it and reset the counter to zero and start over again.
Obviously the update rate on the tach is one minute. Not so hot.

However if we look at the 100 teeth on the ring gear we can
get the up date time (rate) down to 1/100th of a minute or
.6 second. This is the tach for me. I am working on it:)

I used this idea about 35 years ago in my real time road test equipment.
All done in hard ware. No math need be done by a computer.

http://www.rotaryeng.net/IEEE-****road-test-sys.pdf<http://www.rotaryeng.net/IEEE-**road-test-sys.pdf
<http://**www.rotaryeng.net/IEEE-road-**test-sys.pdf<http://www.rotaryeng.net/IEEE-road-test-sys.pdf

A stand alone device so no computer needed either.

Paul Lamar

Paul

Not sure if this, or similar item can work. It has resolution to 0.1 rpm.
http://www.amazon.com/Digital-****Tachometer-Contact-**revolution-**<http://www.amazon.com/Digital-**Tachometer-Contact-revolution-**
minute/dp/B0045E0GT2<http://**www.amazon.com/Digital-**
Tachometer-Contact-revolution-**minute/dp/B0045E0GT2<http://www.amazon.com/Digital-Tachometer-Contact-revolution-minute/dp/B0045E0GT2

Henry

We need cockpit display and remote sensing. They don't tell you the update
rate or the max RPM. LCD's are sometimes hard to read in bright sunlight.

------------------------------****----------------------------**--**------

These are very bright displays.
This board is 2 inches wide (50 mm)  and about .7 inches high.
The characters are 1/2 inch high. It will not take up much room
on your instrument panel.

Here is a preliminary PC board.  There will be another one behind it
with the rest of the circuitry.

Ed, if you build this I won't :)

Paul Lamar



I would build them, I guess your attachment of the board did'nt stick. Can
I
see it  please?

Ed Carver

I did not know you made PC boards Ed Carver. The note was intended for Ed
Anderson.
Ed Anderson is already making several useful instruments for aircraft.

If you, Ed Carver, want to build it feel free. I am thinking of maybe
making
a batch of PC boards and selling them as part of a kit. I would rather not
:)

Here is the latest preliminary design.

Looks like the small surface mount dips are hard to get so I'll go
back to the old full size DIP 16 and use a .8 inch high super bright LED
instead.
Certainly eases the PC board design. The displays are a bit more around
$3.40 each.
The CD4026 is 50 cents each. They will be a few more cheap chips for the
complete and final
design. The crank angle sensor (looking at the ring gear) can be a anti
lock brake
sensor (ABS) at around $25 in the auto parts store. Works as well as a $100
Mazda CAS :)

Paul Lamar



It appeared from the text that there were small boards available for
purchase that could be stuffed for our purposes. Although I could create my
own circuit boards if I were hell bent to do so, I typically have larger
things to do and build.

I usually prefer building things myself if it is cost effective, so I save
all of these email for future reference when time allows. So yes, a kit is
ideal for me. The megasquirt display is available that way, and I notice
there are many such single source displays available on ebay. Kinda pricey
though.

Ed Carver