Ever want an inexpensive tachometer that can remotely sense rpm? I am in the process of building a rolling test stand to try out the CVT (variable drive ratio pulley as used in snowmobiles, etc.) that drives my prop and need to monitor both engine and propeller rpm. Like most projects, I’m trying not to raise the national debt buying parts for it. Having been involved in model airplanes for a long time, I had an optical tachometer on hand and decided to try moving the sensor to the end of a 3-foot extension. The first attempt was made with a Royal digital tachometer.
Although it worked fine, this was a 15-year-old three-digit tach, and I wanted something a bit more precise than the three-digit format. Three Turnigy tachs were ordered for a total cost of about $30. They are much smaller, display four digits, and will read anything between two- and nine-bladed props.
Here’s how to add the extension:
2. Cut the sensor wires and tin the ends of the extension. I have not experimented with the maximum extension length. Mine are about 3 feet long and seem to work fine.
3. Solder the sensor to the extension and the extension to the printed circuit board where you cut off the sensor. Use the smallest soldering iron possible. Excess heat will fry the sensor. I know because I have one dead sensor. Clever of me to order three units. Use heat shrink tubing on the sensor wires.