I built a 'Anemometer and Wind-Vane Wind-Speed and Direction Logger' as part of a RoadTest on the Texas Instruments MSP-EXP430FR4133 LaunchPad development kit and the ADS7042 Ultra-Low Power Data Acquisition BoosterPack.
While implementing a method that required a potentiometer to measure wind-direction and rotation of a DC-motor to measure wind-speed I came across a critical requirement that the shafts of both sensors needed to be co-axial.
I present here a novel method of creating a one-wire potentiometer based on reuse of a small universal-motor commutator-brush assembly. This approach has the important advantage that the central core of the commutator-shaft can be hollow permitting an additional shaft to be co-axially located within this hollow core. However, because of the limited number of commutator segments it provides indication of only a fixed number of discrete angles.
This method is based on separating only the commutator and shaft from a motor assembly and then soldering fixed resistors between commutator segments forming a ring of resistors. If one end of this ring is grounded and a commutator brush used as the other contact we get a resistance variation with rotation angle. This angle can be measured using suitable electronic circuitry.
I purchased a burnt out electric-Mixie motor assembly for INR 75 ( ~ 1$). The main criteria I used in selecting a suitable assembly was to look for something compact, with a large number of commutator-segments and a fairly undamaged commutator surface and brush assembly.
The assembly had 24 commutator-segments which would permit indicating wind direction in angles of 360/24 or 15 degree steps.
The shaft was around 8 mm (5/16 ") which would permit drilling of a 5 mm (3/116") hole through the central core.
I first dis-assembled the Mixie and separated out the armature-commutator-shaft portion. Then while holding one end of the shaft I used hand-tools available with me to separate out the commutator and shaft.
After rough cleaning-up I used a multi-meter to check that there was no short between commutator segments and no connection from any commutator to the shaft.
The parts were now ready for drilling out the central core from the shaft.