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.