Specifications

47
CONSTRUCTION
Fig. 3: Actual-size, single-sided PCB layout for the circuit shown in Figs 1 and 2
Fig. 4: Component layout for the PCB
high and resets IC4(a) to make Q high
again. This starts the motor again.
But if water still does not flow into
the OHT this time, Q of IC4(a) becomes
low again to switch off the motor. Simul-
taneously, IC5 gets another clock pulse
and IC4(a) is reset once again after 10
The output of IC9 is used to switch
‘on’ the speaker at the set frequency. The
frequency (tone) can be set using preset
VR4. The Q output of IC4(b) is also used
to light up the ‘Motor Fault’ LED D27.
This fault condition can be reset by press-
ing switch S2 to reset IC4(a) and IC4(b),
seconds to restart the motor. If this con-
dition repeats for the third time, pin 7 of
IC5 goes high, to reset it. The same out-
put from pin 7 of IC5 functions as a clock
pulse for IC4(b), to give a logic high sig-
nal to RESET pin 4 of IC9 (NE555), con-
figured as astable multiviberator.