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Coqui conductivity sensor

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What Does It Do?

The Coqui: a simple device to read a sensor via an audible tone. We're exploring using audio frequencies to convey sensor readings -- like a modem, but even simpler -- in order to make sensor readings more accessible for people (or to enable data transmission over ubiquitous audio jacks on PCs and smartphones).

Latest version

The latest and simplest version of the Coqui can be seen in the following images. This version differs from the previous in a few ways:

  • smaller, cheaper circuitboard (breadboard)
  • fewer wires
  • flatter wires which make it easier to see the circuit

However, the circuit is fundamentally the same! Click these images to enlarge:

IMG_20190123_111639_270.jpg IMG_20190118_205609_421.jpg

Assemble the Coqui

Here are a few guides to building different versions of the Coqui:

Coqui versions

The Coqui has been refined, remixed, and modified plenty over the years.

Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.

Modify the Coqui

Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.

Do something with the Coqui

Once you've built a Coqui, here are a few things you can do with it:

Add an activity or request an activity guide you don't see listed

Frequently Asked Questions

Title Author Updated Likes Comments
How can we adjust the volume of the coqui? @liz over 5 years ago 7
How can we adjust the frequency of the coqui? @liz over 5 years ago 3
Did anyone feel a strong heating of the buzzer in the Coqui sensor? is too hot @alejobonifacio about 2 years ago 0
Why does my coqui not change frequency in salt water anymore? @stevie almost 4 years ago 2
Can anyone tell what is wrong with my coqui? @stevie about 5 years ago 13
DIY Salinity Measurements with Coqui and/or Multimeter? @Bronwen about 5 years ago 3
Can we use a guitar tuning app to get numeric data from the Coqui water sensor? @warren about 5 years ago 4
Could we just use the PWM feature of an Arduino to generate the 50% duty cycle we need for the Coqui or for a water conductivity meter? @roberts_ecofarm over 5 years ago 3
Will this single timer work for the coqui? @asnow about 6 years ago 5
How much are Coqui measurements affected by hot/cold water? @warren over 9 years ago 14
Accessible procedure for calibrating conductivity measurements? @donblair almost 10 years ago 3


A Coqui is a simple, inexpensive, open source device that generates an audible tone that is based on any electric resistance-based measurement. For example, a Coqui can measure:

  • conductivity of liquids
  • temperature
  • ambient light

Build a Coqui

Instructions on the breadboard-based "BBv1.0" edition of the Coqui can be found here:


  • The github repo for a more permanent printed circuit board version of the coqui is here

The Coquí is a circuit that allows you to 'hear' the readings from various sensors. Once the Coquí is assembled, you'll be able to 'hear' the conductivity of a solution, the temperature of a room, or the color of a pH test strip.

The design was named (onomatopeically) after the several species of small frogs which have a loud, distinctive call at night.

Demo Coqui applications


Building your own Coqui

Building Coqui sensors

Parts list

See the initial parts list here: #13459 and #11209 for a DigiKey shopping cart link at $19 per kit. And @kanarinka mentions:

there are a couple other things that are helpful to have that are not shown (like the probe made from the top of a water bottle with two screws in it and alligator clips to attach that to the breadboard)

Scans of an invoice from DigiKey: