Public Lab Wiki documentation



Coquí: A Simple Water Conductivity Sensor

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This is a beginner's guide to assembling the Coquí

The Coquí is a simple water conductivity sensor designed 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 water conductivity is higher and lower frequency sounds when the conductivity is lower.

Want to measure something other than water conductivity? With simple modifications a Coquí can measure temperature, ambient light and LED light. Check out Don's original post to learn how.

Who is this for?

Buillding a coquí is a great way to introduce principles of water monitoring, DIY hardware, and sensors to new audiences. @kanarinka and John Keefe use coquís to teach workshops in sensor journalism. The coquí is featured in the Educator's Guide to Sensor Journalism pamphlet by @kanarinka (forthcoming from Public Lab Press in Fall 2016).

Duration

Assembly will take around 30-45 minutes for a novice, including troubleshooting and debugging.

Ingredients

Ingredients.jpg

Step-by-step guide to assembling the Coquí

Attach the 555 chip on the breadboard.

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Connect pin #4 to VCC.

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Connect pin #8 to VCC.

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Connect pin #2 to pin #6.

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Connect the speaker to pin #3 and GND.

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Connect pin #3 to some row.

6_revert.jpg

Connect pin #2 to a row right below previous.

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Add a capacitor from previous pin to GND.

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Connect pin #1 to GND.

9_revert.jpg

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

10_revert.jpg

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

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

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DONE!

Step by Step Instructions for Making the Coqui's Probe

The probe is the part of the coquí that you dip in water to measure its conductivity. The coquí actually passes a low-voltage electric current through the water and the two screws in the water bottle cap measure the resistance of that current. You can fashion a simple DIY probe using the following materials:

  1. Plastic water bottle with plastic cap
  2. Scissors or Xacto knife
  3. 2 screws of the same size

Cut the top part off the water bottle using the scissors or knife

cutbottle.jpg

Screw the two screws into the top of the water bottle.

Bottle_with_screw.jpg

Attach the alligator clips leading from the coquí to the bottom of the two screws

probe_with_clip.jpg

Now you have your probe!

Learn more about the Coquí in context

Are you more advanced? Check out this circuit diagram

buzzerDiagram.png