Specifications

CONSTRUCTION
58
allotted 3.5-second time, the output of IC5
becomes 0100 and the connected device
turns ‘on’. At this stage, the parallel in-
put is 0100 and therefore, on parallel load-
ing, the output of IC5 keeps the device in
the ‘on’ state.
Even if a total of seven claps occur
(i.e. three more claps after the device is
‘on’), the counter remains loaded with
0100, thereby resetting the device to its
previous state. Thus, once the device is
‘on’, it requires a total of four claps within
3.5 seconds to turn ‘off’ the device. This
happens because at the fourth clap count,
the output reaches 1000 (from its previ-
ous output of 0100). As a result, Q
D
be-
comes ‘high’, and IC3 and IC5 are reset
to their initial state.
Diode D5 is used to reset flip-flop 1 of
IC3, once IC4 has been triggered. Tran-
sistor T2 is used to reset flip-flop 2 of IC3
when a LD pulse has been applied to IC5.
Manual reset switch S1 (tactile type) is
used to switch off the connected device,
at any instant. It thus serves as an ‘emer-
gency off’ switch.
Precautions. The microphone should
be soldered as close to the PCB as fea-
sible, using shielded wire. Heat-sink
should be provided for the regulator IC2.
If you desire to change the timings within
which claps should occur, use the formula
given below to calculate the values of tim-
ing resistor R and capacitor C for the
pulse width of a monostable flip-flop us-
ing timer IC NE555.
t = 1.1 RC seconds
where t is the time for which output goes
‘high’, R is the value of R17 in ohms, and
C is the value of C13 in farads.
Finally, a switch across ‘common’
and ‘N/O’ contacts of the relay may be used
to bypass the smart clap switch, if desired.
Actual-size, single-sided PCB for
the circuit shown in Fig. 1 is given in
Fig. 2. Component layout for the PCB is
given in Fig. 3.

Fig. 2: Actual-size, single-sided PCB layout for the circuit
Fig. 3: Component layout for the PCB
cause Q
C
output (connected to C input)
would still be ‘low’ when load input be-
comes active low, at the end of 3.5-second.
period. Thus 0000 is loaded into IC5, thereby
keeping the relay or the device connected
to the switch in its previous state.
This happens up to a total of three
claps occuring within the allotted time du-
ration of 3.5-seconds. But if three more
claps occur after the first clap, within the
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