Chapter 5: Building a Touchless Handwash Timer

In Chapter 4, Building a Plant Watering System, we learned how the ADC interface works, and we used that knowledge to write libraries for a capacitive soil moisture sensor and a water level sensor. We also wrote a small library to control a buzzer and learned how relays work and used that knowledge to control a pump using our code. Then we used all this knowledge to build an automated plant watering system.

In this chapter, we are going to build a touchless handwash timer. After working through this chapter, you will know how ultrasonic sound sensors work and how to measure distance with them. We are going to utilize this knowledge to create a sensor that recognizes a hand that is between 20 and ...

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