Introduction: Low Cost Water Flow Sensor and Ambient Display

Water is a precious resource. Millions of people do not have access to clean drinking water, and as many as 4000 children die from water contaminated illnesses every day. Yet, we continue to be wasteful with our resources. The overarching goal of this project is to motivate more sustainable water use behavior and raise awareness about global water issues.

This is an instructible on how to crudely detect water flow in a pipe and drive an ambient display. I am using a piezo transducer, some LED's and an arduino. The device is a rough prototype of what will eventually become a persuasive technology that motivates sustainable behavior and raises awareness about water use.

This is a project by Stacey Kuznetsov and Eric Paulos at the Living Environments Lab, at Carnegie Mellon University Human Computer Interaction Institute.

Produced by
Stacey Kuznetsov

Eric Paulos

Living Environments Lab

The video below illustrates a previous version of this project, where a microphone is used instead of a piezo element to detect water flow. You will achieve better performance when using a piezo transducer, so this instructible details the piezo approach.

Special thanks to Briam Lim, Bryan Pendleton, Chris Harrison and Stuart Anderson for help with ideas and design of this project!

Step 1: Gather Materials

You will need:

- Breadboard
- Microcontroller (I used an Arduino)
- Mastic
- Piezo Transducer (
- A few LED's (I used 2 yellow, 2 red, 2 green)
- Candle holder or similar-sized container
- Wire
- 1 Mohm (or other large value) resistor
- 4.7K Resistors (3)
- 1K Resistors (1)
- Low-value Resistors (for the LED's)
- Clipping Wires
- Jumper Wires
- Mastic
- op amp (LM613)

Step 2: Build the Circuit

The circuit consists of an amplifier to increase the signal from the piezo and a voltage divider to lift the base voltage.

There is a high-value resistor between the two inputs form the piezo, which acts as a pull-down resistor for the signal.

Step 3: Test the Circuit

Attach the piezo to the circuit, and hook up the arduino.

The voltage divider sets the base voltage at 2.5V, so the base readings for the signal should be around 512 on the Arduino analog pin (half way between 0 and 1023). Mine fluctuates +/-30 around 520. You may see some fluctuation around this number.

Step 4: Calibrate Your Sensor to Detect Vibrations

When the tap is turned on, the vibrations of the pipe will cause the piezo to generate a fluctuating current. Since the base reading tapers off around 520, you can compute an amplitude around this number to detect vibrations. My threshhold is set at 130, but you may increase or decrease this depending on the types of vibration you want to sense and sensitivity of your particular piezo piece.

To test the signal, use mastic to attach piezo to a flat surface. Try tapping or scratching on the surface at different locations and different intensities see what type of readings you get on the Arduino.

To reduce noise, I recommend computing a moving average of the input. This is a crude way of determining wave amplitude that avoids false positives due to random static current. More advanced methods such as FFT may also be used.

// Sample Code
int sensor = 2; // Analog in
int val =0; // Current reading for analog pin
int avg; // Running average of the wave amplitude
int MIDPOINT = 520; // Base reading

void setup() {
avg = MIDPOINT; // set average at midpoint

void loop() {
val = analogRead(sensor);

// Compute wave amplittue
if (val > MIDPOINT) {
val = val - MIDPOINT;
} else {
val = MIDPOINT - val;

// compute running average fr the amplitute
avg = (avg * 0.5) + (val * 0.5);

if (avg > 130) {
// vibration detected!
delay(100); // delay to ensure Serial port is not overloaded

Step 5: Create an Ambient Display

If your sensor is working properly, you can add an ambient display to show the information.

My LED's are paired such that each color is illuminated by two LED's. To do this, attach the 'in' (short) lead of each color together, and use a low-value resistor before connecting to the Arduino. Connect the ground (longer) lead of all LED's and attach to ground on the Arduino.

Once the LED's are connected, use the candle-holder to house the display. Since the candle holder is made of aluminum, you may want to put an insulator such as a piece of plastic, on the bottom of the container before inserting the LED's to prevent the circuit from shorting out.

Step 6: Use Sensor Data to Drive the Display

It takes me about 10 seconds to wash my hands. Thus, I have programmed the display to show a green light for the first 10 seconds after the tap is turned on. After 10 seconds, the yellow LED"s turn on. The display turns red if water remains on after 20 seconds, and begins flashing the red light if the tap remains running for 25 seconds or more.

Use can your imagination to create alternative displays!

Step 7: Mount the Sensor and Display Onto a Water Pipe

Use mastic or clay to attach the piezo to the tap, and another layer of mastic to secure the display on top.

You may have to readjust your threshold amplitude or 'MIDPOINT' from step 4. The signal may also be slightly affected by the temperature of the pipe.

Step 8: Future Suggestions

You may choose to drive the Arduino off a battery. An upcoming tutorial will show you how to run this display by drawing power directly from the running water itself, or by harnessing surrounding ambient light energy!

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