A easy way to find out if the Overhead Water Tank or Water
Sump is full. It uses the mild conductivity of water to bias a
This was done in my early days, i have upgraded it, it ought to work, reduce the number of transistors to make it less sensitive, also a lower value in place of 10M will reduce its sensitivity, use clamping diodes to protect.
BD139 is used to drive the relay as it has good Ic. So you can even use a low ohm relay. If a Relay resistance is high its quality is higher, its power consumption is less and it needs thinner wire SWG-AWG. T2 and T3 form a darlington pair which drives T1.
LED1 shows that the water level has reached the top of tank
and also that the Relay is energised. D1 a freewheeling diode.
R3 10M ensures that the high gain input does not float, yet
the low leakage current thru the water is not drawn away by
the 10M. R2 limits base current in case water is saline.
The Source file is here del00006.zip
There is a control signal and an output for relay, if you are
using just a buzzer for alarm, no relay needed. A buzzer, LED or
Lamp can be driven by Transistors.
20th May 2020
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