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Clap
Remote
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infra-red or wireless remote control has the disadvantage
that the small, handy, remote transmitter is often misplaced.
The sound operated switch has the advantage that the transmitter
is always with you. This project offers a way to control
up to four latching switches with two claps of your hand.
These switches may be used to control lights or fans
or anything else that does not produce too loud a sound.
To prevent an occasional loud sound from causing malfunction,
the circuit is normally quiescent. The first clap takes
it out of standby state and starts a scan of eight panel-mounted
LEDs. Each of the four switches are accompanied with two
LEDs one for indicating the on and the other for indicating
the off state. A second clap, while the appropriate
LED is lit, activates that function. For example, if you
clap while LED10 used in conjunction with Lamp 1 is lit
then the lamp turns on. (If it is already on, nothing
happens and it remains on.) A condenser microphone, as
used in tape recorders, is used here to pick up the sound
of the claps. The signal is then amplified and shaped
into a pulse by three inverters (N1 through N3) contained
in CMOS hex inverter IC CD4069. A clock generator built
from two of the inverter gates (N5 and N6) supplies clock
pulses to a decade counter CD4017 (IC2). Eight outputs
of this IC drive LEDs (1 through 8). These outputs also
go to the J and K inputs of four flip-flops in two type
CD4027 ICs (IC3 and IC4). The clock inputs of these flip-flops
are connected to the pulse shaped sound signal (available
at the output of gate N3). Additional circuitry around
the CD4017 counter ensures that it is in the reset state,
after reaching count 9, and that the reset is removed
when a sound signal is received. Outputs of the four flip-flops
are buffered by transistors and fed via LEDs to the gates
of four triacs. These triacs switch the mains supply to
four loads, usually lamps. If small lamps are to be controlled,
these may be directly driven by the transistors. If this
circuit is to be active, i.e. scanning all the time, some
components around CD4017 IC could be omitted and some
connections changed. But then it would no longer be immune
to an occasional, spurious loud sound. The condenser microphone
usually available in the market has two terminals. It
has to be supplied with power for it to function. Any
interference on this supply line will be passed on to
the output. So the supply for the microphone is smoothed
by resistor-capacitor combination of R2, C1 and fed to
it via resistor R1. CD4069, a hex unbuffered inverter,
contains six similar inverters. When the output and input
of such an inverter is bridged by a resistor, it functions
as an inverting amplifier. Capacitor C2 couples the signal
developed by the microphone to N1 inverter in this IC,
which is configured as an amplifier. The output of gate
N1 is directly connected to the input of next gate N2.
Capacitor C3 couples the output of this inverter to N3
inverter, which is connected as an adjustable level comparator.
Inverter N4 is connected as an LED (9) driver to help
in setting the sensitivity. Preset VR1 supplies a variable
bias to U3. If the wiper of VR1 is set towards the negative
supply end, the circuit becomes relatively insensitive
(i.e. requires a thunderous clap to operate). As the wiper
is turned towards resistor R4, the circuit becomes progressively
more sensitive. The sound signal supplied by gate N2 is
added to the voltage set by preset VR1 and applied to
the input of gate N3. When this voltage crosses half supply
voltage, the output of gate N3 goes low. This output is
normally high since the input is held low by adjustment
of preset VR1. This output is used for two things: First,
it releases the reset state of IC2 via diode D1. Second,
it feeds the clock inputs to the four flip-flops contained
in IC3 and IC4. In the quiescent state, IC2 is reset and
its Q0 output is high. Capacitor C4 is charged positively
and it holds this charge due to the connection from R5
to this output (Q0). IC2 is a decade counter with fully
decoded outputs. It has ten outputs labelled Q0 to Q9
which go successively high, one at a time, when the clock
in put is fed with pulses. IC3 and IC4 are dual JK flip-flops.
In this circuit they store (latch) the state of the four
switches and control the output through transistors and
triacs. At the first clap, the output of gate N3 goes
low. Diode D1 is forward biased and it conducts, discharging
capacitor C4. The reset input of IC2 goes low, releasing
its reset state. All the J and K inputs of the four flip-flops
are low and so these do not change state, even though
their clock inputs receive pulses. When the reset input
of IC2 is low, each clock pulse causes IC2 to advance
by one count and its outputs go high successively, lighting
up the corresponding LEDs and pulling high the J and K
inputs of the four flip-flops, one after the other. Resistor
R8 limits the current through LEDs 1 through 8 to about
2 mA. Larger current might cause malfunction due to the
outputs of IC2 being pulled down below the logic 1 state
input voltage. If a second clap is detected while the
J input of a particular flip-flop is high, its Q output
will go high, regardless of what state it was in previously.
Similarly, if its K input was high, the output will go
low. (If both J and K are high, the output will change
state at each clock pulse.) Thus although all flip-flops
receive the clap signal at their clock inputs, only the
one selected by the active output of IC2 will change state.
Resistor R9 and capacitor C6 ensure that the flip-flops
start in the off state when power to the circuit is switched
on, by providing a positive power-on-reset pulse to the
reset input pins when power is applied. The preset input
pins are not used and are therefore connected directly
to ground. When, after eight clock pulses, output Q8 of
IC2 becomes high, diode D2 conducts, charging capacitor
C4, thereby resetting IC2 and making its Q0 output high.
And there it stays, awaiting the next clap. The four Q
outputs of IC3 and IC4 are buffered by npn transistors,
fed through current limiting resistors and LEDs (to indicate
the on/off state of the loads) to the gates of four triacs.
Four lamps operating on the mains may thus be controlled.
For demonstrations, it might be better to drive small
lamps (drawing less than 100 mA at 12V) directly from
the emitters of the transistors. In this case the triacs,
LEDs and their associated current limiting resistors may
be omitted. It has to be noted that one side of the mains
has to be connected to the negative supply line of this
circuit when mains loads are to be controlled. This necessitates
safe construction of the circuit such that no part of
it is liable to be touched. The advantage is that it may
be mounted out of reach of curious hands since it does
not need to be handled during normal operation. It is
advisable to start with the low voltage version and then
upgrade to mains operation, once you are sure everything
else is working satisfactorily. CMOS ICs are used in this
circuit for implementing the amplifying and logic functions.
Use of a dedicated supply is recommended because the integrated
circuits will be damaged if the supply voltage is too
high, or is of wrong polarity. An external power supply
may get connected up the wrong way around, or be inadvertently
set to too high a voltage. Therefore it is a good idea
to start by constructing the power supply section and
then add the other components of the circuit. If the clock
is working, you may turn your attention to the amplifier.
LED9 should be off, and should flash when the terminals
of capacitor C2 are touched with a wet finger (the classic
wet finger test). Preset VR1 may need to be adjusted until
LED9 just turns off. The output of gate N2 will be at
about half the supply voltage. The output of gate N3 would
normally be high. The voltage at the input of gate N3
should vary when preset VR1 is varied. High-efficiency
LEDs should preferably be used in this circuit. The microphone
has two terminals, one of which is connected to its body.
This terminal has to be connected to circuit ground, and
the other to the junction of resistor R2 and capacitor
C2. These wires are preferably kept short (one or two
centimetres) to avoid noise pickup. With the microphone
connected, a loud sound (a clap) should result in LED9
blinking. Adjust preset VR1 so that LED9 stays off on
the loudest of background noises but starts glowing when
you clap. If the clap-to-start feature is not required,
it may be disabled by omitting components D1, D2, R5,
C4 and connecting a wire link in place of diode D2. Then
IC2 will be alive and kicking all the time. . |
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