Hi Nitin,

Well Steve has beat me to it and has given you the schematic ( in full color!).

My scheme was almost similiar except for the following changes :

1. The Oscillator was replaced by a simple 12V ac signal from a transformer winding.

2. C1 was omitted and C2 was 1.0 uF/35V non-polarized. This value was required as the ac frequency was only 50 Hz.

3. The output of D2 was provided with a 10 uF which takes care of some additional hysterisis when the water level is *just* falling or *just* raising and avoids relay chatter. ( Erik's suggestion to use a +ve feedback comaparator will also do this )

4. The signal was then fed to a comparator using LM311 which served as a sensitivity adjustment and also a level translator.

5. Using the same ac source for all probes (high level, low level, dry flow etc) is what I did. But to maintain equal sensitivity in all cases the sensing was always done with 2 probes : one common and the other sensing. Kindly note that the distance between probes, water conductivity are variables that affect sensitivity. Out of this the water conductivity can vary quite a bit and hence keep the other variable constant.

6. SAFETY : Take all care to use a GOOD quality double insulated Transformer for the ac source. AND even then the common point must have a 5mA fuse, to take care of the eventuality of direct short from the 230V primary.

Hope that helped.

Raghu