how to use a digital tachometer with an arduino

Using Arduino Project Guidance
3

It would probably be easier to do without the laser tach. Just use an LED and phototransistor.

  1. super-bright crystal clear LED fed with 5V through 180 ohm resistor
  2. Phototransistor fed with a 100K ohm resistor from 5V to collector, emitter to ground
  3. Take output of collector - resistor junction to Arduino input.
  4. Place both LED and phototransistor next to each other pointing in the same direction with a bit of back tape between them.
  5. Point them at the fan blade, from short distance (2cm-3cm)
  6. Read the pulses coming off the phototransistor

Something like that.