Full part list (Arduino based RPM meter)

IR LED and senosr: LINK eBay
Arduino NANO: LINK eBay
LM324 amplifier: LINK eBay
Push button: LINK eBay
Slide button: LINK eBay
OLED screen: LINK eBay
30AWG wire: LINK eBay
Cheap lser diode: LINK eBay
9V battery connector: LINK eBay
9V battery: LINK eBay
drilled PCB: LINK eBay