This adapter allows interfacing a modern potentiometer type wind vane to the Heathkit ID-1590 wind speed/direction console in place of the very hard to find and expensive original Heathkit sensor boom. I used NRG sensors and modified the anemometer by installing a reed switch in place of the pickup coil because I happened to get a good deal on them but the vane/anemometer used with the Davis VantagePro weather stations should be a direct fit without modification and can be purchased new for much less than finding an original Heathkit boom. I calibrated the anemometer by strapping to the top of my car while a passenger adjusted the calibration pots in the ID-1590 and found this to be surprisingly accurate all the way up to 70 MPH which is the fastest I tried. The adapter is designed so that it can draw phantom power from the unmodified Heathkit console with no external power source required. The circuit is designed the way it is because Heathkit used a clever trick to multiplex 8 lamps controlled by 8 reed switches in the wind vane over 5 wires by usind diodes to split the lamps into two banks using the two half cycles of the AC waveform from the power transformer.
The prototype was designed on the fly and hand built on a pefortated prototyping board. Because I only needed one, I did not bother laying out a PCB however the KiCAD schematic is included so somebody can do this if desired. Most of the component values are not critical at all and most of the parts I used in the prototype were stuff I already had on hand. Some care does have to be taken to keep the load on the 3.3V power supply as low as possible in order to utilize phantom power from the console so a regulator with low dropout and low quiescent draw is needed. This arrangement depends on the fact that the ID-1590 uses incandescent lamps for the wind direction indication and these are able to flow enough current to power the circuit through the inactive lamps without causing them to glow. If your console has been modified with LEDs you may need a different approach to power the adapter due to the fact that LEDs will visibly glow at extremely low current.
The code is written in C using AVR Studio and a compiled hex file is provided that can be loaded directly on the ATMEGA8. The clock needs to be set to 1MHz using the internal R/C oscillator in order to keep current consumption low.