Want to build a simple clap switch circuit that will toggle any load in response to your claps? The article is presented exactly for this purpose. Here we discuss 4 unique and simple designs which can be selected as per user preference.
The article talks about what the title suggests – a clap switch. A small electronic circuit when built and integrated to any electrical appliance can be made to switch ON/OFF through mere hand clapping.
The entire procedure is explained here in. You have seen magicians doing this, a “clap” and the object vanishes. Obviously I am not here to teach you magic, however the present circuit is nothing less than a magical device, well certainly can be for the children.
The proposed design when integrated to any of your electrical appliance can be used to switch it ON and OFF simply through alternate clapping of your hand. The device becomes more interesting and useful because it does not require any external mechanism or device to carry out the specified operations.
As you must have noticed the clapping of hands creates a loud sound and is sharp enough to move quite a distance. The generated sound is in fact strong ripples or vibrations created due to the sudden compression of air in between our striking palms.
The circuit presented here is basically made up of two stages, the first stage is a two transistor hi-gain amplifier and the second stage consists of an efficient flip/flop.
A mic is connected to the amplifier stage; the sound vibrations made by clapping hits the mic and get converted into tiny electrical vibrations. These electrical pulses are amplified to suitable levels by the transistors and are fed to the flip/flop.
The flip/flop stage alternately switches the output relay driver in response to every subsequent clapping. The load connected to the relay thus also gets activated and deactivated correspondingly.
The circuit may be further understood with the following explanation.
1) Using IC 741.
The above clap operated relay circuit was provided to me by one of the keen readers of this blog Mr. Dathan.
The circuit is very to understand:
The opamp here is configured as a comparator, meaning it is positioned to differentiate the slightest of voltage differences across its two inputs.
When the clap sound hits the mic, a momentary drop of voltage is experienced at pin#2 of the IC, this situation raises the voltage at pin#3 of the IC for that instant.
As we know, with pin#3 at higher potential than pin#2 makes the output of the IC high, the condition puts the output of the IC go high momentarily.
This high response triggers the IC 4017 pin#14, and forces its output to either move from pin#2 to pin#3 or vice versa depending upon the initial situation of the outputs.
The above action switches the load accordingly either to ON or OFF position.
The above 12V clap triggered switch circuit using IC 741 was successfully tried and tested by Mr. Ajay Dussa. The following prototype images for the same were sent by Mr. Ajay.
The PCB design (track layout) for the above can be seen below, as designed by Mr. Ajay:
2) Using Transistors or BJTs
In the above explanations we learned a simple clap activated switch circuit which incorporated an IC for implementing the desired flip flop actions. The present design uses a different principle and utilizes only transistors for the above triggering actions.
R1 = 5k6
R2 = 47k
R3 = 3M3
R4 = 33K
R5 = 330 OHMS
R6 = 2K2
R7 = 10K
R8 = 1K
R9, R10 = 10K
C1, C4 = 0.22uF
C2 = 1uF/25V
C3 = 10uF/25V
T1, T2, T4 = BC547
T3 = BC557
All IC diodes = 1N4148
Relay diode = 1N4007
IC = 4017
Relay = 12v / 400 ohms
How it Works
The figure above shows a straight forward two stage sound activated switch.
The first stage comprising T1, T2, and T3 forms a hi-gain voltage amplifier configuration.
A mic is connected at the base of T1 via blocking capacitor C1.
Strong sound vibration hitting the mic is instantly picked and converted into tiny electrical pulses.
These are in fact small AC pulses easily make there way through C1 into the base of T1.
This creates a kind of push-pull effect and T1 also conducts in the corresponding way.
However the response of T1 is relatively weak and requires further amplification.
Transistors T2/T3 are introduced exactly for this and help to improve the voltage peaks created by T1 to appreciable levels (almost equal to the supply voltage.)
The above voltage pulse is now ready to be use for toggling the flip flop and is fed to the relevant stage.
IC 4017 as we all know produces sequential shifting of its output pin-outs (logic high) in response to every positive pulse at its clock input pin 14.
The amplified clap sound voltage pulse is applied to pin 14 of the above IC, this flips the output of the IC to either a logic high or a logic low depending upon the initial status of the relevant pin-out.
This triggered output is appropriately collected at the diode junctions abd used to toggle a relay through a relay driver transistor T4.
The relay contacts ultimately goes to a load or an appliance which is correspondingly switched ON and OFF with every subsequent claps.
Using BJTs and Power Supply
Looking at the circuit diagram we see that the entire circuit has been configured around ordinary general purpose transistors.
The functioning of the circuit may be understood with the following points:
Transformer X1 along with the D1 and the capacitor C4 forms the basic power supply circuit for providing the required power to the circuit.
The first stage which includes R1, C1, R2, R3, R4 and Q1 form the input sensor circuit.
The next corresponding stages consisting of Q2 and C3 form the flip flop stage and makes sure that the signals from the input sensor stage is appropriately converted into alternate toggling of the output.
The output stage consists of a single transistor Q4. It is basically configured as a relay driver stage for translating the flip flop actions from the previous stage into physical toggling of the connected load across the relay terminals.
The design is very old, I built it in my school days by assembling a kit. The circuit diagram using transistors is shown in below:
R1 - 15K
R10, R3 -270K
R4 - 3K3
R6 - 27K
R7,R11 - IK5
R8,R9 - 10K
R13 - 2K2
C3, C1 - 10KPF Disc
C2,3 - 47KPF Disc.:
C4 - 1000uF/16V;
Q1,2,3,4 - BC547B
D1 - 1N4007
D2,3,4,5 -1N4148 _
Xl - 12V/300mA Transformer .
MIC - Condenscr Mic
RLY — 12V Single Charge over relay
Another version of the above can be seen in the following diagram:
3) Double Clap-Clap Switch Circuit
All the clap on switch circuits explained above have the ability to operate only with single alternate clap sounds. This feature makes the circuit vulnerable to external sounds which might occur occasionally triggering the connected load with the circuit.
A double clap operated circuit thus becomes more suitable and resistant to spurious triggering due to the fact that it would toggle only in response to two subsequent clap sounds instead of one.
The explained circuit is simple yet effective and does not employ microntrollers for the implementation unlike other circuits on the net.
The circuit has been tested by me, but it is a fairly complex design it's important to first understand the stages convincingly, and then build it to avoid failures.
The proposed clap-clap circuit or double clap circuit functioning may be understood with the following points:
The lower stage is basically a simple sound activated switch circuit which would activate with any loud sound.
The IC 741 is rigged like a comparator with its pin#2 referenced at some optimal fixed potential determined by the setting of the given preset VR1.
Pin#3 of the IC becomes the sensing input of the IC and is connected with a sensitive mic.
The adjoining IC 4017 is a flip flop stage which activates the connected relay driver stage and the load alternately in response to every positive high pulse at its pin#14.
When a loud sound such as a "clap" hits the mic, it momentarily grounds pin#2 of the IC741 resulting in a momentary high pulse at its pin#6.
If we connected this output to pin#14 of IC4017 would have resulted in an instant toggling of the load with every single sound input which we don't want here to happen, therefore the response at pin#6 of IC741 is broken and diverted to an IC 555 monostable stage.
How IC 555 is Configured
The IC 555 circuit is rigged in such a way that when its pin#2 is grounded, its output pin#3 becomes momentarily high for some period of time depending upon the values of the 10uF capacitor.
When a sound hits the mic, the high pulse from IC741 output triggers the BC547 attached to pin2 of IC555 which momentarily grounds pin#2 of IC555, which in turn put its pin#3 high.
However the instantaneous high at pin#3 of IC555 takes a while to reach the connected BC547 due to the presence of the 33uF capacitor.
By the time the 33uF charges and switches ON the transistor, the potential at the collector of the transistor is already gone due the absence of the clap sound which happens only momentarily.
However with the application of the immediate subsequent clap provides the required potential at the collector of the transistor which is now allowed to the reach pin#14 of the flip flop IC 4017.
Once this happens the relay driver triggers or deactivates depending upon its initial condition.
The toggling of the load thus takes place only in response to a pair of clap of sounds making the circuit reasonably foolpoof.