The smart pressure sensor is the key to this compression tester. It
 is a smart sensor in that it puts out zero to five volts making it
 compatible with the Maximite analog to digital input pins.

 It cost about $50 at mouser. About the same price as the Maximite
 :-)

 The Maximite program to read  and record it many times a second
 shortly.

 Paul Lamar

 Here it is along with the pressure sensor wiring. Data is in
 atmospheres I think. Data is printed on the screen but it would
 normally go to a file on the SD card. It is comma delimited so it can
 be loaded into a spread sheet and plotted.

 The hard ware interrupt comes in every 200 ms or 5 times a second.
 Could be up to 1000 a second or 1 ms. There is lots of space on that
 32 gig SD card :-)

 Super simple.

 Paul Lamar


 The barometric pressure is up this morning. I added time and date to
 the file from the battery backed up clock  as well as labeling it
 rotor 1.

 For the EFIS version you could calculate density altitude.

 Paul

 Here is the other thing you need. If you cut off the rolled over
 steel section at the base of the ceramic the ceramic will fall out.
 Press in a brass rod and machine it down for the silicon rubber hose
 connection.

 Paul Lamar

 That 1/16th ID silicon hose did not work out. The compression blew it
 off. I safety wired it on and the hose broke :-)

 I ordered some 1/8th ID reinforced "high pressure"  PVC from
 mcmaster. I'll try that.

 Paul Lamar


Hi Paul
Haven’t done any calcs but check the volume of any hose used. At some point it will begin to effect the waveform read.
Perhaps given the transducer has builtin amplifiers and temp comp etc. locate it closer to the plug hole,
maybe with a small length of tube to reduce vibration.

Just thunking
Steve Izett

I'll try it Steve and see if it makes a difference. That is difficult to do with the TTC engine and
that 84 inch prop :-) That is one heck of a pressure  pulse.

I discovered one thing that Geof did not mention in the doc.

It is possible sometimes to get an erroneous  non input pin  error message
if settick is before setpin. Particularly if the settick period is short. Say below 200 ms.

That had me baffled for awhile. I thought the A to D pin was damaged.

It is good idea to do all the set up before settick is invoked. You might mention
that to Geof the next time you communicate with him. It is not in the doc.

One other thing. The sensor puts out 0 to 5 volt. The input pins are
only good to 0 to 3.3 volts so a resister divider is needed. The sensor out put is
indeed in PSI above whatever atmospheric pressure is.

The data up loaded so far is wrong due to 5 volts applied to the input pin.
 When I get the new tubing I will up load the right data.

Paul Lamar


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