Our Bearhawk is going to need two little circuits that I’m going to try and make. The first is a low-voltage warning module. They Dynon EMS has a built-in warning for low voltage, but this little circuit will be a stand-alone warning for a system that is fairly important. I used the Bob Nuckolls designed 9005 module. I ordered the circuit board for both circuits (and the e-bus diode) from Bob earlier this fall, and ordered the components from Digikey. I had to make a few substitutions due to availability from Digikey, but I was able to find all of the parts. I’ve had all of these parts for a few months, but today is my first working day that is just too cold for being in the hangar!
The low voltage module serves a simple role. It illuminates a flashing LED on the panel (in my case, two) whenever the battery is on, but the alternator isn’t. This is an indication to the pilot that he/she is running on limited stored battery energy instead of generated and therefore relatively unlimited alternator energy. The airplane will also be in this condition on the ground when the engine isn’t running, so it will help me remember to turn off the master after shutdown. I added all of the components to the circuit board, but I got one of the resistors wrong.
The second circuit is an audio isolation amplifier. This will consolidate the audio output of the various sources (GPS, Dynon, Ipod, etc) and provide a feed for the intercom’s single input. The board has provisions for resistors of different value, which will allow volume adjustments for each channel.
I wasn’t able to test the audio amp yet, but I made up a test rig for the low voltage module out of an old computer cable. It doesn’t work yet, but I’ve got some good leads on how to fix it.