Hey everyone

So I am having trouble with this project of mine. Basically, I need an LED to turn on when water is not present (dries out). So first I need this to happen with just a bowl of water (oh and I cannot add salt at any point). Then need it to also work with a bowl of wet sand, bowl of wet paper towels, soil, etc. So I took a 9v and ran a copper wire at each end of the bowl and then to a 9v normally open relay, however it only works when the wires are touching, it's not conducting through the water. Then tried it with a 3v relay, same problem... Hmmm.

Any help would be greatly appreciated!

 

Until someone comes up with a better idea, do a web search for LM339 comparator circuits. I think it is sensitive enough. You may find a circuit that you can use. The output on or off depends on which input you use.

 

While regular water does conduct electric current, it does not do it very well. The current through the water is not enough to do much of anything directly. The signal has to be amplified and compared against a reference voltage to determine if there is enough current to equate to the presence of water (or damp materials). Because passing DC through water causes electrolysis and other chemical reactions, the signal through the water usually is an AC signal, either a sinewave or square wave. This makes detection a bit more complex, but not much. The innergoogle has many circuits for water detection. Modifying one to reverse the action of the indicator is a minor change.

ak

 

Hey everyone

So I am having trouble with this project of mine. Basically, I need an LED to turn on when water is not present (dries out). So first I need this to happen with just a bowl of water (oh and I cannot add salt at any point). Then need it to also work with a bowl of wet sand, bowl of wet paper towels, soil, etc. So I took a 9v and ran a copper wire at each end of the bowl and then to a 9v normally open relay, however it only works when the wires are touching, it's not conducting through the water. Then tried it with a 3v relay, same problem... Hmmm.

Any help would be greatly appreciated!

Simple problem use an alternating current like a block two advantages:
a: no problem with electrolyse
b: pure water acts like a bad capacitor so it has an impedance.
take two metal bars one to gnd separate and isolate 1 cm approx.
generate a block feed this via resistor and capacitor into a metal bar not connected to gnd.
use opamp measure between resistor and capacitor.
This is a measure for water level. that's all.

 

You need to use an AC detection system like this...when water is present the led lights up, take the led from output to ground to make it on when no water detected.

circuit

Swap the opto-coupler for a led or transistor and relay.

 

There is a wealth of material on the internet:

https://www.google.co.uk/search?q=p...KEwik9YL2m5_LAhWGIpoKHU7VCsUQ_AUIBSgA&dpr=0.9

 

You need to use an AC detection system like this...when water is present the led lights up, take the led from output to ground to make it on when no water detected.

http://www.simplecircuitdiagram.com/wp-content/uploads/2010/10/Optocoupler1.gif

Swap the opto-coupler for a led or transistor and relay.

Thanks Dave,
I've been trying to give this a shot and am still having trouble... I think this might be beyond my capability. Would you be able to walk me through this a little further? I hope we can work something out!

Thanks again,

 

Ok what have you got done at the moment?

 

Here is a link to a water level detector circuit. It looks like it's for detecting water level in fish tank, but might work for you as well.
http://pinvolt.com/960gs/MySite/Pro...terLevelSensorWithAlarm/WaterLevelSensor.html

 

The post #9 linked circuit uses DC energisation of the probes. That will result in relatively rapid corrosion of the probes. Dave's suggested circuit in post #5 is better.

 

Post#5 circuit again....

 

You know what, I'm not ready to give up just yet! Give me a few more days and I will get back to you....

 

Ok what have you got done at the moment?

Ok, I'm having trouble correctly placing everything in my breadboard... Ugh, I feel like I've tried this every which way now. My board goes from A-J, 0-60. Is there anyway you can help walk me through the placement of each item?
Thanks!

 

Photo of your current layout...?

ak

 

Project : Pet Water Dish Alarm Sensor

This is very close to what you describe.

After 4 months I have noticed some corrosion on electrodes, thin wire used for picture hanging, but they still work. When I designed this I planned on replacing the electrodes periodically.

 

Photo of your current layout...?

ak

Alright so keep in mind I am new to bread boarding and electronics lol. Feel like I got about halfway there... Please help, and I apologize but I'm probably going to need very specific instructions...

 

Post#5 circuit again....

Thanks Dave

Ok what have you got done at the moment?

So admittedly I haven't made it very far, I am obviously new to electronics but have posted a picture of where I'm at...