Posted by Circuits Arena on Friday, 14 November 2014
Water Alarm Circuit Using LMC555 IC is the artlcle explaining Water Alarm Circuit This circuit made by IC LMC555, which is a CMOS version of the bipolar 555 timer chip and followed by a complementa...
Water Alarm Circuit
- This circuit made by IC LMC555, which is a CMOS version of the
bipolar 555 timer chip and followed by a complementary pair of
emitter followers (T1 and T2) to drive a standard 8-ohm speaker (LS1).
Power is supplied by a compact 9V PP3 battery.
- Power is applied when power switch S1 is closed. The reset input (pin 4)
of IC1 is held low by resistor R1 (2.2-kilo-ohm). The astable
oscillator wired around IC1 is in disabled mode.
- When probes P1 and P2 become wet, these conduct to reverse the state of
IC1’s reset terminal. As a result, the astable multivibrator starts
oscillating at a frequency determined by resistor R2 and capacitor C3.
- The output of IC1 drives the complementary pair of transistors T1 and T2.
- A 10-kilo-ohm potentiometer (VRI) is inserted between output pin 3 of
IC1 and the bases of transistors T1 and T2 for volume control.
The probes can be made using two suitable copper needles or small pieces
of circuit board with the copper surface coated with solder.
- Fit these at the lowest point where water will accumulate. After
construction, place the alarm circuit well away from the point of
possible leakage. Use a pair of thin twisted flexible wires to connect
the probes to the circuit.
- Capacitor C1 connected across IC1 input (pin 4 and GND) keeps the alarm circuit from responding to stray electrostatic fields.
- Similarly, twisting the wires together makes the relatively long
connection between the probes and the circuit less sensitive to false
alarms due to external electromagnetic interference. Finally, if you
want to lower the probe sensitivity, reduce the value of grounding
resistor R1.
