This is where you may need to get a little creative. Every machine is different, so you will need to examine your machine to find a good place to mount the sensor and display.
If the controls on your machine run on low-voltage DC, you may be able to tap into that to power your tach. Otherwise, you will need a separate DC power supply. The Pro Trinket can run on anything in the 5v-12v range.
You will also need an enclosure of some sort for the processor and display. There are lots of small project boxes that could work well here. Or, if you are inspired, you could design a custom 3D printed one to fit your machine.
Most machinery has one or more belts and pulleys between the motor and the final drive spindle. These may increase or decrease the speed relative to the motor. Ideally, the sensor should be attached so that it can monitor the rotation of the final drive spindle. Below are a few examples:
Lathe Mounting:
For this small lathe, we created a target pattern on the headstock handwheel using black photographer's tape.
We left one small gap in the tape so that the chromed surface would reflect IR back to the sensor once per revolution.
The sensor is mounted to a strip of brass spring-stock and positioned just a couple millimeters from the target on the handwheel.
Drill Press Mounting:
For this 17" drill press, the final drive pulley was already painted black. So we just added a white patch* on the edge.
The sensor is screwed to the base of the pulley shroud - using a small wooden spacer block to align the sensor with the edge of the pulley.
The display is mounted to the base of the pulley shroud - just above eye level.
*Tip: Wite-Out ™ or similar error correcting fluid is quick drying and opaque - which makes it perfect for this application.
Band Saw Mounting:
The main drive wheel on this 14" band-saw was also conveniently pre-painted black. So all we needed was a spot of white error-correcting fluid on the edge.
The sensor is screwed to a wooden block which is sized to position it a couple millimeters from the rim
Note: For a band-saw, you will be interested in the linear blade speed rather than the RPM. To calculate the blade speed in surface feet per minute (SFPM) multiply the RPM by the circumference of the drive wheel as in the code below:
if (revCount > 0)
{
rpm = 60000000 / (accumulator>>3);
}
// calculate SFPM assuming diameter is in inches
int sfpm = (rpm * diameter * Pi) / 12;
Serial.println(sfpm);
matrix.println(sfpm);
matrix.writeDisplay();
Enclosure and Display Mounting:
The best location for the display will vary from machine to machine. Choose a location with good visibility - but out of the way so that it does not create a safety hazard or interfere with normal machining operations.
For the prototype, I've mounted all the electronics (except for the sensor) in a small translucent project box (Hammond #1591). This is affixed to the base of the lathe near the power switch. Wiring is routed under the chassis and away from any moving parts.
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