This is a beginner's guide to assembling the Coquí

The Coquí is a simple water conductivity sensor by @donblair that is designed for use in an educational context. The coquí is a simple circuit assembled on a breadboard that has a speaker that outputs high frequency sound when the conductivity is higher and lower frequency sounds when the conductivity is lower.

A Coqui can measure conductivity, temperature, ambient light and LED light.

Coqui BBv1.0 is a version of the Coqui that is made on a breadboard, with just a few simple parts. Learn how to make one below!

Ingredients

Resistor (R) tunes the frequency of the 555 output (which we'll be hearing via a speaker)

For low conductivity solutions, 0.1 uF in a capacitor (C) is a good range to use. For higher conductivity solutions (like salt water), 1.0 uF, or even 10.0 uF, might be better values to use, in order to keep the output frequency in the audible range.

The frequency of the output is a function both of the resistance, 'R' (which can be either a resistor, or some water between two electrodes, or a photo-resistor, or a thermistor, or a potentiometer ... anything that will provide an electrical connection, with some resistance), and a capacitor, 'C'.

The frequency of output is given by: 0.7/(R*C).

Step-by-step guide to assembling the Coquí

Attach the 555 chip on the breadboard.

Connect pin #4 to VCC.

Connect pin #8 to VCC.

Connect pin #2 to pin #6.

Connect the speaker to pin #3 and GND.

Connect pin #3 to some row.

Connect pin #2 to a row right below previous.

Add a capacitor from previous pin to GND.

Connect pin #1 to GND.

Using a photocell as a sensor: add the photocell between the previous two wires.

Connect the battery (positive / red to VCC, negative / black to GND).

Place an LED between VCC and GND to make sure there's power, when debugging (Optional).

DONE!