This is a beginner's guide to assembling the Coquí
The Coquí is a simple water conductivity sens...
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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.
This post, originally by @akshaya and @kanarinka, is being reposted from this wiki page in order to integrate with the new activities system
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.
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 (download here).
Assembly will take around 30-45 minutes for a novice, including troubleshooting and debugging.
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:
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Hi, I reposted this from https://publiclab.org/wiki/coqui-a-simple-water-conductivity-sensor -- to make it into an activity that can be featured in the Coqui activities listing: https://publiclab.org/wiki/coqui#Activities -- to help @kgradow run a class based on this.
I hope I got it right -- if it should be authored by @kanarinka and co-authored by @ashkaya, please tell me and I can switch it. Thank you -- it's a WONDERFULLY documented activity!
This is a great overview! One suggested edit: Include an explanation of how component variability might impact the circuit. I've tried to build this circuit literally dozens of times and about half the time it fails because my resistor / capacitor values are incorrect or I haven't taken into account speaker resistance or I've gotten the wrong voltage for the 555 and burnt out the timer or it's simply not making a tone in the audible range.
One solution is to post a set list of components -- better would be to post some explanation of which components matter and what acceptable parameters are (for resistors, capacitors, tolerance on the 555, and power) so that people actually can drop in whatever components they have on hand. As written it suggests that that's possible, where there seem to be a lot of fail points that are relatively easy to hit if you're not taking ranges into account.
Thanks @warren! @kgradow1 - this is a great suggestion for improvement as I've also had that happen. How about @akshaya and I will make a digikey shopping cart with all the parts and then people can go look at it for reference? (Do those stick around for awhile?)
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I'm intrigued by the speaker resistance - can that be measured with a multimeter - and what are the rules of thumb for not burning out the timer?
I'm actually not sure about this - @donblair - do you know the answer?
I haven't had great luck with Digikey shopping carts sticking around, so it might be better to put direct links to parts in e.g. a wiki ...
Re: burning out the timer, haven't had that happen myself (I don't think?) but I guess you'd just want to be careful to stay within the voltage limits of the 555. There might also be ways of applying a reverse voltage to the wrong pins which could make the 555 decide to curl up and die.
E.g., for this version, looks like the voltage inputs need to be between 2V and 15V.
@kanarinka - we're planning to order a bunch of these to test out at MakeFaire SF at the end of may -- getting ready for a big order, and printing up the guide as well -- quite a few of them. Happy to share!
Hi! I made a bookletized version of the pdf for printing on half-letter-sized paper --
Added a 3.5mm jack to record the wave ;D
This is really cool. A recording would mean you could calibrate it later, too -- if you maybe dipped it in 2 different high and low solutions of known conductivity at the start or end of each test? Like a 🎬 before a film clip!
Deffinitely! On wednesday i'll post the mod ;)
A bit late but here is how to plug the jack https://publiclab.org/notes/imvec/06-08-2018/adding-a-jack-to-the-coqui
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