Make Every Week: Audible Water Sensor

In just a few weeks, a class of journalism students will be wading into West Virginia streams to deploy water sensors.

They’ll be sensing water conductivity over several weeks using a cool, Arduino-like board called Riffle.

But the crux of the system is a simple circuit I tried for the first time tonight.

Gimme Five-Five-Five

This is exceptionally easy to build, if you have the right parts. (Here’s a parts list!) And the heart of the parts is a tiny chip called a “555.”

Don Blair, who designed the Riffle, describes the 555 as kind of “metronome.” Wired up correctly, it’ll “click” at different speeds given different resistances.

That’s useful because water with more “stuff” in it tends to be less resistant than clean water. So less resistance (the opposite of conductivity) can be a proxy for turbidity — cloudiness — and possibly pollution.

Wiring it Up

I followed the instructions Don posted on the Public Lab site, with some minor changes:

  • I replaced this 10 uF capacitor with a 0.1 uF capacitor (as he suggests in the text)
  • I replaced the light sensor with a pair of wires I could stick into water

Update 9/22/2016: Here are step-by-step wiring instructions I've been using in recent presentations.

Remember, the 555 “clicks” at a different rate for different resistances — and if it clicks fast enough, it becomes a tone.

If you haven't already done so, check out my test run with tap water vs. black coffee in the video above!

#MakeEveryWeek is a challenge to myself to do just that for all of 2015. The original post on the idea is here, and the running list of projects is here.