Friday, 28 September 2012

Installing Instrumentation for Dragon III

Circuit board mounted off to the side
of the engine compartment
Terminal block to bring all
the connections up to the bulkhead
I had some trouble with the instrumentation on the engine early in the season, and never had a tachometer, so I decided I would try to monitor them electronically as a challenge. Here's what the actual installation looked like.

The experience of hookup and testing proved interesting. I wired everything up and it worked, giving believable output for the tach, which changed as the engine speed changed in very believable ways, so I felt good. Then I disconnected the tach circuit and the Arduino kept registering the same data anyway! WTF!

Moving away from the engine reduced the indicated RPM and towards the engine increased it. With the input wire on the Arduino unterminated, there was enough electrical noise that it was picking it out of the air like an antenna, with voltages high enough to generate an interrupt. Don't let anything float - pull it high or low!

An additional wire to get the signal from the negative side of the coil.
The coil and wiring create enormous electrical noise!