I needed a tacho/RPM display for a CNC spindle. I decided to use an Arduino Micro and OLED display with a reflective LED/Photo transistor as a sensor. Since powering up, a clock can display the total running time of the machine. (or this can be reset via a push button.)
I completed the first version and its working well!
Its using an Arduino Micro, making it easy to develop or customise sandwiched onto a PCB carrying the Voltage regulator etc and an OLED display on the other side.
Since most hobbyist does not have access to SMD stations, this is is through-hole project - apart from the Arduino Micro - but this just plugs in.
Most of the Arduino pins have been extended to a solder pad and two push button switches can be added, one perhaps for resetting run time statistics. This should make it possible to add or apply this in other areas using different sensors.
Still to Do
The board can be designed to support maybe a few other sensor types like Hall effect for example. Its also easy to add more channels and add any other controls like relays etc. I would like to send the pulse on to Mach 3 - the control software for the CNC machine.
In my prototype board I had a bug (due to my PCB design library) with the pinouts on the Voltage regulator. The schematic is correct and I have updated the PCB files here.