Sensors

$0.20

The simplest and cheapest way of detecting light is with the use of photoresistor, join 2 or more together to make light chasing or line following robot. It has 10-20k ohm resistance in ligh and 1M ohm in darkness.

$0.50

Use this condenser microphone for your arduino project if you would like to build sound detector or you can of course use it for any other audio project.

$0.35

This receivers are ideal for obstacle detection sensor on your robot. Since they only detect 38kHz IR pulses there is no danger of false detections due to sun. Combined with 3 or 5mm IR LED you can make reliable obstacle sensor at an unbelievably low cost.

$0.30

This guys are not as accurate as LM35 but they still come in handy for detecting overheat on your motor driver IC or any other component that tends to overheat.

$0.15

In combination with 38kHz IR receiver module they make great obstacle sensor. They are cheap but they get the job done!

$0.25

Just like 5mm IR LEDs you can use this 3mm LEDs to make sensor for your robot. The only difference is that they are slightly less powerful than 5mm version but a lot smaller which can make them better choice over 5mm brothers.