# water activated electronic switch help

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#### eightwgt

##### New Member
I want to make a simple switch - one that will upon completing a circut light a LED light (very small one)

I am trying to make a very accurate water level that when the water level reaches a pin head and ANY surface contact is made between water and the pin head a circuit is completed...

How can I do this... ( Im not an electronic person)

THANKS in advance for any help !

Tom

#### Klaus

##### New Member
Tom, there would be lots of ways to do that, perhaps the simplest is a float switch, especially if you are not an electronics person.
Float switches are commercially available.
If that is not accurate enough you need to give more info, eg. what kind of water (fresh, salt, sewage etc.) what kind of tank or container, does the water level rise slowly or is it agitated and why the accuracy, in other words, what is it you're measuring?

Klaus

#### eightwgt

##### New Member
klaus

Yes I am aware of float switches..... I need HIGH accuracy - Here is what I need a circuit for

I want to power it with say a 9 volt battery

The contacts will be in a clear acrylic tube - one at bottom.... the other will be a needle - like a sewing needle set in a rubber cork verticle so when water in tube rises and makes ANY contact with the point it lights an LED....

I am making an electric water level and need a very sensitive switch so I get top accuarcy...... take a needle and look very close at the top of a glass of water and BARELY touch the surface.... you wll see it 'dimple' the surface...... I want it sensitive enough so as soon as it makes any contact at all, it completes a circuit....
I looked and lie detector circuits and some other stuff, have a few ideas, but as I said Im not at all up to par on electronic circuits and what would work best since I only have a VERY basic understanding of it all......

Thanks

Tom

#### Klaus

##### New Member
Tom, if you can add a little salt to the water it conducts quite well and you can use the water itself to carry the switch current. You'd need to drive the base of a transistor with it so the LED can be turned on by the transistor.

Being *that* accurate, you'd have to make sure there is no vibration at all for false triggering.

Or, you could float a reflective disk on the water and have a LED sensor above trigger your signal as soon as the disk floats close enough and reflects the LED light back to a light sensor. The LED and sensor are angled from each other of course, they are available as a ready made unit.

The latter is possible as accurate but a less troublesome than your needle contact idea. There is no electrical contact in the water at all and you can easily slide the sensor up or down above the water surface to fine tune this thing.

Klaus

#### kirby89

##### New Member
I have already done this using a store bought water sensor/alarm. The sensor was bought at a Home Depot type store for $9-$10. It uses a 9V battery. The audible alarm is triggered when moisture is detected between the sensor's electrodes on the bottom of the unit. I modified the alarm by wrapping the bared ends of 2 wires on the sensor's electodes & then ran the wires into my tube. The wire insulation was also bared on the ends running into the tube. Distance between the wires sensor ends needn't be precise. This was a very easy-quick project to do. In your case you need to replace the alarm's audible transducer w/ a LED. Desolder the transducer, & solder the LED into the circuit w/ a variable resistor of perhaps 1.5 kohms. Set the variable resistor at its highest setting & lower the resistance w/ the sensor actuated by moisture. The LED should start to light dimly as you approach its minium current. Continue to tune the variable resistor(potentiometer or pot)until the LED is sufficiently bright. You might want a couple spare LEDs as this type of tuning might allow for to much current, burning the LED out. The variable resistor or "pot" should be a linear taper design & not a audio taper. Audio would be much trickier to work w/. Good Luck

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