Clap On Clap Off Switch using 555 Timer IC
A
"Clap On Clap Off" switch is an interesting concept that could be used
in home automation. It works as a switch which makes devices On and Off
by making a clap sound. Although its name is “Clap switch”, but it
can be turned ON by any sound of about same pitch of Clap sound. The
main component of the circuit is the Electric Condenser Mic,
which has been used as a sound sensor. Condenser Mic basically converts
sound energy into electrical energy, that in turns used to trigger 555
timer IC, through a Transistor. And triggering of 555 ic works as a
Clock pulse for D-type flip-flop and would turn ON the LED, which will
remain ON until the next clock pulse means until the next Clap/sound. So
this is the Clap Switch which will turn ON with first Clap and turn OFF
with the second Clap. If we remove the D-type Flip flop from the
circuit, the LED will be turned OFF automatically after some time and
this time will be 1.1xR1xC1 seconds, which I have explained in my previous circuit of clap switch. For better understanding, I recommend to study the previous circuit before study this one.
Clap On Clap Off Switch using 555 Timer IC
A
"Clap On Clap Off" switch is an interesting concept that could be used
in home automation. It works as a switch which makes devices On and Off
by making a clap sound. Although its name is “Clap switch”, but it
can be turned ON by any sound of about same pitch of Clap sound. The
main component of the circuit is the Electric Condenser Mic,
which has been used as a sound sensor. Condenser Mic basically converts
sound energy into electrical energy, that in turns used to trigger 555
timer IC, through a Transistor. And triggering of 555 ic works as a
Clock pulse for D-type flip-flop and would turn ON the LED, which will
remain ON until the next clock pulse means until the next Clap/sound. So
this is the Clap Switch which will turn ON with first Clap and turn OFF
with the second Clap. If we remove the D-type Flip flop from the
circuit, the LED will be turned OFF automatically after some time and
this time will be 1.1xR1xC1 seconds, which I have explained in my previous circuit of clap switch. For better understanding, I recommend to study the previous circuit before study this one.
Working Explanation
Here we are using Electric Condenser Mic for
sensing the sound, transistor to trigger the 555 timer IC, 555 IC to SET
& RESET the D-type flip flop and D-type flip flop to remember the
logic level (LED ON or OFF) until next Clap/sound.
Here we are using Electric Condenser Mic for
sensing the sound, transistor to trigger the 555 timer IC, 555 IC to SET
& RESET the D-type flip flop and D-type flip flop to remember the
logic level (LED ON or OFF) until next Clap/sound.
Components
Condenser Mic
555 Timer IC
Transistor BC547
Resistors (1k, 10k, 47k, 100k ohm)
Capacitor (10uF)
IC7474 more precisely DM74S74N (D-type flip flop)
LED and Battery (5-9v)
Condenser Mic
555 Timer IC
Transistor BC547
Resistors (1k, 10k, 47k, 100k ohm)
Capacitor (10uF)
IC7474 more precisely DM74S74N (D-type flip flop)
LED and Battery (5-9v)
Circuit Diagram and Explanation
You can see the connections in above "clap on clap off circuit diagram".
Initially the transistor is in OFF state because there is not enough
(0.7v) base-emitter voltage to turn it ON. And the point A is at high
potential, and point A is connected to Trigger pin 2 of 555 IC, as a
result Trigger pin 2 is also at high potential. As we know that, to
trigger the 555 IC through Trigger PIN 2, the voltage of the PIN 2 must
be below Vcc/3. So at this stage no output at OUT PIN 3, means no clock
pulse for D-type Flip-flop (IC 7474), thereby no response from D-type Flip-flop, and so LED is OFF.
Now when we produce some sound near condenser mic,
this sound will be converted into electrical energy and it will raise
the potential at the Base, which will turn the Transistor ON. As soon as
the transistor becomes ON, the potential at Point A would become low
and it will trigger the 555 IC because of the low voltage (below Vcc/3)
at Trigger Pin 2. So the output PIN3 will be high and a positive clock
pulse will be applied to D-type Flip-flop, which makes Flip-flop to
respond and LED will turn ON. This SET state of flip flop will remain as
it is until the next clock pulse (next Clap). Detailed working of
D-type Flip-flop has been given below.
Here we are using 555 timer IC in Monostable Mode,
whose output (PIN 3 of 555 IC) has been used as a clock pulse for
D-type Flip-flop. So the clock pulse will be HIGH for 1.1xR1xC1 seconds
and then it would become LOW. You can learn 555 IC operations through
some 555 timer circuits .
You can see the connections in above "clap on clap off circuit diagram".
Initially the transistor is in OFF state because there is not enough
(0.7v) base-emitter voltage to turn it ON. And the point A is at high
potential, and point A is connected to Trigger pin 2 of 555 IC, as a
result Trigger pin 2 is also at high potential. As we know that, to
trigger the 555 IC through Trigger PIN 2, the voltage of the PIN 2 must
be below Vcc/3. So at this stage no output at OUT PIN 3, means no clock
pulse for D-type Flip-flop (IC 7474), thereby no response from D-type Flip-flop, and so LED is OFF.
Now when we produce some sound near condenser mic,
this sound will be converted into electrical energy and it will raise
the potential at the Base, which will turn the Transistor ON. As soon as
the transistor becomes ON, the potential at Point A would become low
and it will trigger the 555 IC because of the low voltage (below Vcc/3)
at Trigger Pin 2. So the output PIN3 will be high and a positive clock
pulse will be applied to D-type Flip-flop, which makes Flip-flop to
respond and LED will turn ON. This SET state of flip flop will remain as
it is until the next clock pulse (next Clap). Detailed working of
D-type Flip-flop has been given below.
Here we are using 555 timer IC in Monostable Mode,
whose output (PIN 3 of 555 IC) has been used as a clock pulse for
D-type Flip-flop. So the clock pulse will be HIGH for 1.1xR1xC1 seconds
and then it would become LOW. You can learn 555 IC operations through
some 555 timer circuits .
Working of D-type Flip-flop
Here we are using Positive Edge Triggered D-type flip-flop, which
means this flip flop only responds when clock pulse would go from LOW
to HIGH. OUTPUT Q will be shown according to state of INPUT D, at the
time of the Clock pulse transition (Low to High). Flip flop remembers
this OUTPUT state Q (Either HIGH or LOW), until the next positive clock
pulse (Low to High). And again shows the OUPUT Q, according to the input
state D, at the time of clock pulse transition (LOW to HIGH)
D-type Flip-flop is basically the advanced version
of S-R flipflop. In S-R flipflop, the S=0 and R=0 is forbidden, because
it is making the flip-flop behaving unexpectedly. This problem is
resolved in D-type Flip-flop, by adding a Inverter between both the
inputs (see the diagram) and the second input is given by the Clock
pulse to both the NAND gates. Inverter is introduced to avoid same logic
levels at both the inputs, so that “S=0 and R=0” condition never
occurs.
D-type Flip-flop doesn’t change its state while
clock pulse is low, because it gives the output logic level “1” at NAND
gates A and B, which is the input for NAND gates X and Y. And when both
the inputs are 1 for NAND gates X and Y, then output don’t change
(remember S-R flip-flop). The conclusion is that it will not change its
state while clockpulse is LOW, regardless of INPUT D. It only change
when there is transition in Clock pulse from LOW to HIGH. It won’t
change during the HIGH and LOW period. We can deduce the truth table for
this D-Flip-flop:
Clk
D
Q
Q'
Description
↓ » 0
X
Q
Q'
Memory
no change
↑ » 1
0
0
1
Reset Q » 0
↑ » 1
1
1
0
Set Q » 1
Here we are using Positive Edge Triggered D-type flip-flop, which
means this flip flop only responds when clock pulse would go from LOW
to HIGH. OUTPUT Q will be shown according to state of INPUT D, at the
time of the Clock pulse transition (Low to High). Flip flop remembers
this OUTPUT state Q (Either HIGH or LOW), until the next positive clock
pulse (Low to High). And again shows the OUPUT Q, according to the input
state D, at the time of clock pulse transition (LOW to HIGH)
D-type Flip-flop is basically the advanced version
of S-R flipflop. In S-R flipflop, the S=0 and R=0 is forbidden, because
it is making the flip-flop behaving unexpectedly. This problem is
resolved in D-type Flip-flop, by adding a Inverter between both the
inputs (see the diagram) and the second input is given by the Clock
pulse to both the NAND gates. Inverter is introduced to avoid same logic
levels at both the inputs, so that “S=0 and R=0” condition never
occurs.
D-type Flip-flop doesn’t change its state while
clock pulse is low, because it gives the output logic level “1” at NAND
gates A and B, which is the input for NAND gates X and Y. And when both
the inputs are 1 for NAND gates X and Y, then output don’t change
(remember S-R flip-flop). The conclusion is that it will not change its
state while clockpulse is LOW, regardless of INPUT D. It only change
when there is transition in Clock pulse from LOW to HIGH. It won’t
change during the HIGH and LOW period. We can deduce the truth table for
this D-Flip-flop:
|
Clk
|
D
|
Q
|
Q'
|
Description
|
|
↓ » 0
|
X
|
Q
|
Q'
|
Memory
no change |
|
↑ » 1
|
0
|
0
|
1
|
Reset Q » 0
|
|
↑ » 1
|
1
|
1
|
0
|
Set Q » 1
|
IC 7474
We have used IC DM74S74N of 7474
series. IC DM74S74N is the Dual D-type Flip-flop IC, in which there are
two D-type Flip-flops, which can be either used individually or as a
master-slave toggle combination. We are using one D-type Flip-flop in
our circuit. Pins for first D flip-flop are the left side and for second
flip flop are at right side. Also there are PRE and CLR pins for both
the D-type Flip-flops which are active-low pins. These pin used to SET
or RESET the D-type Flip-flop respectively, regardless of INPUT D and
Clock. We have connected both to Vcc to make them inactive.
After understanding the D-type Flip-flop and IC DM74S74N,
we can easily understand the use of D-type Flip-flop in our circuit.
When we first triggered the 555 IC by first Clap, the LED glows as we
get Q=1 and Q’=0. And it will remain ON until the next trigger or next
positive clock pulse (LOW to HIGH). We have connected Q’ to to INPUT D,
so when LED is glowing, Q’=0 is waiting for Second Clock pulse, so that
it can be applied to the INPUT D and makes Q=0 and Q’=1, which in turns
TURN OFF the LED. Now Q’=1 is waiting for next clock pulse to make the
LED turn ON by applying Q’=1 to INPUT D, and so on this process will
continue.
To test this circuit you need to clap loudly as
this small condenser mic don’t have long range. Or you can directly hit
at the mic lightly (like I have done in the video).
We have used IC DM74S74N of 7474
series. IC DM74S74N is the Dual D-type Flip-flop IC, in which there are
two D-type Flip-flops, which can be either used individually or as a
master-slave toggle combination. We are using one D-type Flip-flop in
our circuit. Pins for first D flip-flop are the left side and for second
flip flop are at right side. Also there are PRE and CLR pins for both
the D-type Flip-flops which are active-low pins. These pin used to SET
or RESET the D-type Flip-flop respectively, regardless of INPUT D and
Clock. We have connected both to Vcc to make them inactive.
After understanding the D-type Flip-flop and IC DM74S74N,
we can easily understand the use of D-type Flip-flop in our circuit.
When we first triggered the 555 IC by first Clap, the LED glows as we
get Q=1 and Q’=0. And it will remain ON until the next trigger or next
positive clock pulse (LOW to HIGH). We have connected Q’ to to INPUT D,
so when LED is glowing, Q’=0 is waiting for Second Clock pulse, so that
it can be applied to the INPUT D and makes Q=0 and Q’=1, which in turns
TURN OFF the LED. Now Q’=1 is waiting for next clock pulse to make the
LED turn ON by applying Q’=1 to INPUT D, and so on this process will
continue.
To test this circuit you need to clap loudly as
this small condenser mic don’t have long range. Or you can directly hit
at the mic lightly (like I have done in the video).
Some Important Points
- If circuit doesn’t works at first, then connect the CLR (PIN1 of
IC DM74S74N) to the ground to RESET the flip-flop, then again connect
to Vcc as shown in circuit.
- We can modify this circuit using Relay to control the Electronic devices (120/220V AC).
- Control PIN 5 of 555 Timer IC should be connected to Ground through a 0.01uF capacitor.
- We should use a 220 ohm resistor to connect LED.
Video:
- If circuit doesn’t works at first, then connect the CLR (PIN1 of IC DM74S74N) to the ground to RESET the flip-flop, then again connect to Vcc as shown in circuit.
- We can modify this circuit using Relay to control the Electronic devices (120/220V AC).
- Control PIN 5 of 555 Timer IC should be connected to Ground through a 0.01uF capacitor.
- We should use a 220 ohm resistor to connect LED.
Video:
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