I am working to the same end, I have a water cooled pc and want a water level monitor but am taking a different approach.

My reservoir is here http://www.playtech.co.nz/upload/200710260849510.jpg and as you can see is transparent.

I did not want to have any form of probe inside the reservoir as I have been reading that any electrical component there could cause corrosion.

Thus I came up with the idea to use an inverted infra red detection system using http://www.rapidonline.com/netalogue/specs/72-8966.pdf sat at the 2.75 inch mark on the left hand side of the reservoir to send IR light to the right side where it would be picked up by a bank of these:
http://www.rapidonline.com/netalogue/specs/72-8968.pdf

Between the emitter and receiver there would be a clear plastic tube with holes running up the length of it to allow water to run down and air bubbles a place to get out, inside the tube would be a small black plastic cylinder which would be weighted and aprox 1/10th the size of the tube allowing movement of the cylinder up and down blocking a phototransistor.

This signal would then be taken and used to light up an array of normal leds upto the point beneith the phototransistor that was not active.

Thus a water level indicator with no electronics in the reservoir with only the dependancy that the tank be clear. I may also pot the back of the emitter so that light only goes the one way and also stick a label on the receptor side that limites the width of the light allowed in, in addition to turning the phototransistors into a form of array but with each unit light separated for greater accuracy.

I have a little electronics knowledge but would appreciate quite a whack of help.

Your input would be realy appreciated

 

Sorry to post three times in a row but Ive had a punt at it myself ; however I think where I'm currently at will result in d2 not being lit, can someone with a bit more electronic mojo have a look at my circuit at seem if i'm right ?

Cheers all

 

I have moved two of your posts to a new thread. When someone starts posting into an existing thread with a new subject, we term it hijacking and discourage it. It makes replies simply too hard to perform. Always start new threads for new topics.

Your circuit can't possibly work. The emitters of the level indicators need to go to ground. The LED's should be in series with each collector and the associated resistor, with the LED cathode toward the transistor collector.

 

There are a large number of sensors out there, not all have to be emersed. There are also proximity sensors that use capacitance changes to detect something close by.

It is usually easier to by premade rather than to make something from scratch. Companies like McMaster Carr or Grainger have these devices, and also have online catalogs.

 

This might work: