Add a DIY Digital RPM Readout to Your Wood Lathe

Hall effect sensor readout shows RPM values on a 7-segment display.

Jeremy S. Cook
2 months agoSensors

YouTuber Zach (AKA ‘byte sized') purchased a wood lathe off of Craigslist, and while it seems functional enough, one thing it doesn’t have is a digital readout to show the machine’s RPM. As rotational speed is dictated by a pulley system, this type of machine doesn’t typically have such a display, but he decided to get creative and build one himself.

The construction process is outlined in the video below, starting out with prototyping the 7-segment display setup on a breadboard and employing an Arduino Nano as the processing module. He’s using N-channel MOSFETs to drive the common cathodes of each digit here, since this could theoretically draw 80mA, and 470 ohm resistors to limit the current to each segment to less than 10mA.

RPM measurement is provided by a Hall effect sensor that picks up on a magnet attached to the handwheel. This was eventually increased to four magnets in a 3D-printed housing to enable proper sensing.

After the device was prototyped on a breadboard, it was transferred to a PCB and mounted in a 3D-printed housing. A single cable powers the lathe as well as the new readout assembly, using a small transformer to supply 5VDC power. More details can be found in the project write-up, and it should be an excellent addition to Zach’s workspace when his garage warms up!

Jeremy S. Cook
Engineer, maker of random contraptions, love learning about tech. Write for various publications, including Hackster!
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