Brief Description: Gretz Heated Pitot Status Lights - Part 1
I decided to wire the Gretz Heated Pitot Tube status LEDS to the annunciator inputs on the VP-200 rather than use the three LED board supplied with the Gretz kit. But, there was a problem. The Gretz controller outputs a positive voltage when the given indicator is active. The annunciator inputs on the VP-200 all expect to see a connection to ground to activate. Fortunately there is an integrated circuit called an "opto-isolator" (Digikey part number 425-2595-5-ND or manufacture part number PC845XJ0000F) that can handle this very issue. I had to fabricate a small PC board to mount the IC and then add some resistors and wiring and a bit of heat shrink tubing to hold it all together. My goal with the PC board was to make it small and compact enough to actually fit *inside* the DB37 connector housing on the VP-200. It was a tight fit, but fortunately it just fit!
The good news is that all of the work was worth it. I configured the VP-200 with three new annunciator lights, specifically:
Pitot Power (Green)
> VP-200 is powered up pitot controller (Pitot thermostat might be on or off.)
Pitot On - Low (Red)
> Pitot thermostat is ON but temperature is low and element is heating up.
Pitot On - Norm (Yellow)
> Pitot thermostat is ON and pitot is currently de-iced.
So, that finishes the Heated Pitot installation. Works great. I hung a bag of ice over the pitot and sure enough the thermostat kicked on and melted the plastic bag!
Schematic and chip details can be found in the next log entry...
