Public Lab Research note


Simple 555 conductivity meter

by donblair | July 11, 2014 04:16 | 305 views | 7 comments | #10675 | 305 views | 7 comments | #10675 11 Jul 04:16

Read more: publiclab.org/n/10675


I'm going to add some notes to this tomorrow, but just wanted to jot some stuff down.

Recipe for a conductivity meter that blinks an LED at a frequency that is inversely proportional to the conductivity of a solution.

Here's the wiring diagram:

555conductivity-nocap.png

And here's some Arduino code to monitor the output (more explanation tomorrow), as well as measure the temperature (an important variable for conductivity):

https://gist.github.com/dwblair/f0baedb7b8e155b804ae

A preliminary test showed a nice, solid, repeatable relationship between conductivity and the average 555 timer pulse duration (y axis is average pulse duration in seconds, x axis is index of data points, sampled every few seconds -- the probe was initially placed in a higher conductivity solution, then then briefly in a lower conductivity for three separate stretches (indicated by the three higher plateaus)) ...

conductivityjuly14-2.png

... more soon!


7 Comments

Wow, very cool. Does the Arduino monitor it via a light sensor?

I also want to test the new callouts feature: @mathew, did you get a notification for this comment? This is a design for a crazy-low-cost sensor built only around the 555 instead of a microprocessor. Related to the "sensor cricket" idea of graphing via light or sound.

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@kanarinka and I chatted about this idea also at PDF, including found an audio version you could leave a voicemail with at the server to submit data or broadcasting it on an "air quality radio channel".

@kanarinka can you confirm you got an email notification?

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Are you using a spark labs kit?

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I've been offline for the past four days or I would have been all "THIS! THIS!" immediately. because this is awesome! soooooooooo cool. We should see what it costs to do this SMT (smt 555)[http://www.digikey.com/product-detail/en/NA555DR/296-21752-1-ND/1629153]. I bet we can make it super small and with a piezo speaker built in.

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@dorncox and I "riffed" on this idea today in Somerville... can we call it the Riffle Cricket, maybe, referencing that cricket chirps encode the air temperature?

Dorn and I also talked about the potential to put a small solar panel on this and maybe somehow get it to store power until it has enough to "chirp".

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Yay!

@mathew: Great! And we already have a pretty nice relevant smt board design -- coin cell powered, with an RGB led and a piezo buzzer: http://publiclab.org/notes/donblair/03-02-2014/thermal-flashlight-reva-first-tests -- and can easily swap out the microcontroller in that design with a 555 ... it'd also be nice to add a switch that chooses audio jack vs piezo buzzer output, and a switch to choose various capacitors on the 555, so that various conductivity ranges could be addressed ....

@warren -- super! We could easily do that! Super cool ... is there some pre-fab container (single-serving shampoo bottles, or etc) that would be fun and practical as weatherproof containers? We can design the circuit board to fit inside something clever ...

One of the ideas that came up at the workshop was to add an RC high-pass filter on the 555 output, so that it would only 'chirp' when the conductivity spiked above a certain threshold (tuneable, with a potentiometer, and/or a switch among various capacitors) -- this way you could use the device as an 'alarm' in your toilet resevoir -- a super-cheap and simple version of the CATTFISH idea ...

Wheee!

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I got the email notification @warren. So super awesome to see the progress on this

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