Simple Water operated relay
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 Darlington Trio.
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
R2 prevents noise pickup from causing relay
chattering. A small cap could be added across R2 but
this will slow the response time. Inputs of High
gain configurations can be very sensitive to noise,
emi and static.
Made up of only Transistors and Diodes, No Chip at
all. I had to once interface an high voltage circuit
to PC, The uC had to communicate thru RS232--Comm
Water Level with Reed Relays
This design has a Chip but can measure the water
level in stages. It can be used for any fluid unlike
is a Relay - Jim Asks
is an electrically operated switch. Many relays use
an electromagnet to mechanically operate a switch,
but other operating principles are also used, such
as solid-state relays"
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
If you want to operate a big hooter or 230V lamp a
relay is needed- or even a motor or solenoid to move
some thing. Even a Solid State Relay
can be used.