IR reflectance sensor + Sound timer

I’m thinking of making a device that can measure time between…

  1. an IR reflectance sensor being triggered by the passing of a reflective sticker (between 10-20cms away)

  2. and the detection of a short sound from some form sound sensor.

This probably isn’t too complex but as a relative novice I’d greatly appreciate any advice on what sensors to get and how to go about programming+circuitry.

The cheaper the better :stuck_out_tongue:

Thanks, look forward to your replies :slight_smile: