The clap-switch is a device that simply be operated by sound i.e. switch ‘ON’ or ‘OFF’ the connected device through a clap through a clap sound. This is really a miracle for handicapped person. It may be a thing of fun for all age hobbyists. The circuit will switch onoff any appliance connected to it. it. !it may be a bulb" a fan" tape recorder or even a T.# T.#. set $through its relay !acting as a switch$ on the sound of a clap and will switch it ‘off’ on the sound of second clap.
HOW IT WORKS Input Transducer (Microphone The sound of your claps is pic%ed up using an electret microphone. &ome people call it by the name 'condenser microphone. Inside it is an electret film - which is the electrical analogue of a magnet - stretched so that it will vibrate in sympathy with any sound falling on it. These vibrations cause the electrical charge on a perforated plate nearby to change" and a field effect transistor converts these into corresponding changes in current.
A!p"i#ier ( transistor stage" biased near cut-off !that is" almost no current with no sign signal al$$ ampl amplif ifie iess the the sign signal al from from the the micr microp opho hone ne.. The The outp output ut of the the microphone is coupled to the base of the transistor using an electrolytic capacitor !note) using a better capacitor here will not wor%$. The top of the electret microphone is at a few volts" the base conducts at around half a volt" so the lea%age current of the capacitor !all electrolytic capacitors lea% at least a little bit$ will eventually cause the steady state condition in which the lea%age of the capacitor goes into the base terminal of the transistor. &o the collector will have * fe times this lea%age" which can usually be ignored. The first first time time the the microp microphon honee output output goes goes positi positive" ve" howeve however" r" !becau !because se somebody somebody clapped$ clapped$ this change gets coupled to the base entirely entirely due to the action of the capacitor. This causes the current through the transistor to
increase" and this increase in current causes the voltage at the collector" which was sitting near the supply voltage" to fall to nearly +ero. If you clapped loudly enough" of course. This is not a high fidelity audio amplifier. Its function is to produce no output for small sounds and large output for !slightly$ bigger sounds" so the customary biasing networ% can be omitted. The ,. egohm resistor in the previous version was as good as an open circuit" and its omission does not affect the operation of the clap switch in any way. /rovided" of course" that you use that 01 microfarad electrolytic capacitor .
Me!or$ Two cross connected transistors in a bistable multivibrator arrangement ma%e up a circuit that remembers. 2ou can set it to one of two possible states" and it will stay in that state until the end of time. 3hen one transistor conducts" its collector is near ground" and a resistor from this collector feeds the base of the other. &ince this resistor sees ground at the collector end the base at the other end receives no current" so that transistor is off. &ince this transistor is off" its collector is near supply potential and a resistor connects from this to the base of the other transistor. &ince this resistor sees voltage" it supplies the base with current" ensuring that the transistor remains on. Thus this state is stable. 4y symmetry" the other state is" too.
Chan%in% state On a clap" the state of the bistable changes. The output of the amplifier is converted to a sharp pulse by passing it through a !relatively$ low valued capacitor" of 1.0 microfarads !011 nanofarads$. This is connected through 'steering' diodes to the base of the transistor which is conducting. This transistor stops conducting" and the other transistor was not conducting anyway. &o at a clap" both transistors become off. Then" those two capacitors across the base resistors come into action. The capacitor connecting to the base of the transistor which was ON has voltage across it. The capacitor connecting to the base of the transistor which was OFF has no voltage across it. (s the sound of the clap dies away" both bases rise towards the supply voltage. 4ut" due to the difference in the charges of the two capacitors" the
base of the transistor which was previously not conducting reaches the magic value of half a volt first" and it gets on" and stays on. 5ntil the ne6t clap. Two red 7ight 8mitting 9iodes have been placed in the two collector circuits so that this circuit can be made to wor% by itself. If you cover up one 789" and display the other prominently" you have it there - a clap operated light.
Output Sta%e In order to have a decent amount of light from this circuit" I propose to use si6 white 789s in three groups of two each. 8ach series connected string of two 789s is arranged to draw around fifteen milliamperes or so by using a series resistor of ::1 ohms. Two 789s in series will drop about five or si6 volts" and the remaining battery voltage drop across this resistor determines the current through the 789s. 2ou can get more brightness from the 789s by reducing the value to ;;1 ohms or even 0<1 ohms" provided you %eep within the ratings of the 789s. 9o so at your own ris%. Thus the output stage has to handle around fifty or si6ty milliamperes. This will give you fairly long time of claplighting with a //: battery. The 011m( filament lamp seems to be somewhat hard to find" and people were using torch bulbs" which run at much higher current" and %illing their batteries in a few minutes. ( transistor gets its base driven from the collector of one of the transistors in the bistable. 3ith this connection" due to the base current through it" one red 789 in the bistable switches between half bright and full" and the other switches between fully off and on. This is normal. 4ecause the 789s do not draw as much current as a filament lamp" the output transistor" too" can be of the common small signal variety. (ll four could be any small signal n-p-n transistor and the circuit should wor%. &o would it with four p-n-p transistors" provided you switch the polarity of every !polarised$ component
D&SCRIPTION OF COMPON&NTS R&SISTOR ( resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. =esistors can also be used to provide a specific voltage for an active device such as a transistor . (ll other factors being e>ual" in a direct-current ! 9?$ circuit" the current through a resistor is inversely proportional to its resistance" and directly proportional to the voltage across it. This is the well-%nown Ohm@s 7aw. In alternating-current !(?$ circuits" this rule also applies as long as the resistor does not contain inductance or capacitance.
=esistors can be fabricated in a variety of ways. The most common type in electronic devices and systems is the carbon-composition resistor . Fine granulated carbon !graphite$ is mi6ed with clay and hardened. The resistance depends on the proportion of carbon to clayA the higher this ratio" the lower the resistance. (nother type of resistor is made from winding Nichrome or similar wire on an insulating form. This component" called a wirewound resistor " is able to handle higher currents than a carbon-composition resistor of the same physical si+e. *owever" because the wire is wound into a coil" the component acts as an inductor s as well as e6hibiting resistance. This does not affect performance in 9? circuits" but can have an adverse effect in (? circuits because inductance renders the device sensitive to changes in output.
R&SISTOR COLOUR COD&
CAPACITOR ( capacitor is a tool consisting of two conductive plates" each of which hosts an opposite charge. These plates are separated by a dielectric or other form of insulator" which helps them maintain an electric charge. There are several types of insulators used in capacitors. 86amples include ceramic" polyester " tantalum air" and polystyrene. Other common capacitor insulators include air" paper" and plastic. 8ach effectively prevents the plates from touching each other. ( capacitor is often used to store analogue signals and digital data. (nother type of capacitor is used in the telecommunications e>uipment industry. This type of capacitor is able to adBust the fre>uency and tuning of telecommunications e>uipment and is often referred to a variable capacitor . ( capacitor is also ideal for storing an electron. ( capacitor cannot" however" ma%e electrons.
S7M4OL
S7M4OL OF &L&CTROL7TIC CAPACITOR
( capacitor measures in voltage" which differs on each of the two interior plates. 4oth plates of the capacitor are charged" but the current flows in opposite directions. ( capacitor contains 0.< volts" which is the same voltage found in a common (( battery. (s voltage is used in a capacitor" one of the two plates becomes filled with a steady flow of current. (t the same time" the current flows away from the other plate. To understand the flow of voltage in a capacitor" it is helpful to loo% at naturally occurring e6amples. 7ightning" for e6ample" is similar to a capacitor. The cloud represents one of the plates and the ground represents
the other. The lightning is the charging factor moving between the ground and the cloud.
IMA6& OF &L&CTROL7TIC CAPACITOR
UNPOLARIS&D CAPACITORS ( non-polari+ed !'non polar'$ capacitor is a type of capacitor that has no implicit polarity -- it can be connected either way in a circuit. ?eramic" mica and some electrolytic capacitors are non-polari+ed. 2ou@ll also sometimes hear people call them 'bipolar' capacitors.
S7M4OL OF NON POLARIT7 CAPACITOR
TRANSISTORS ( Transistor is an se!iconductor which is a fundamental component in almost all electronic devices. Transistors are often said to be the most significant invention of the ;1th ?entury. Transistors have many uses including switching" voltagecurrent regulation" and amplification - all of which are useful in applications. rene:a;"e ener%$ ( transistor controls a large electrical output signal with changes to a small input signal. This is analogous to the small amount of effort re>uired to open a tap !faucet$ to release a large flow of water. &ince a large amount of current can be controlled by a small amount of current" a transistor acts as an a!p"i#ier . ( transistor acts as a s:itch which can open and close many times per second.
4ipo"ar
S7M4OL OF NPN > PNP TRANSISTOR
7ayers with e6tra electrons are called N?T$pe" those with electrons missing called P?T$pe. Therefore the bipolar Bunction transistors are more commonly %nown as PNP transistors and NPN transistors respectively. 4ipolar Bunction transistors are typically made of si"icon and so they are very cheap to produce and purchase.
Ho: do Transistors Wor@
( bipolar Bunction transistor has three terminals - 4ase" Co""ector" and &!itter corresponding to the three semi-conductor layers of the transistor. The wea% input current is applied to the inner !base$ layer. 3hen there is a small change in the current or voltage at the inner semiconductor layer !base$" a rapid and far larger change in current ta%es place throughout the whole transistor.
/ictured above is a schematic diagram of the more common NPN transistor. 4elow is an illustration of the same transistor using water rather than electricity to illustrate the way it functions)
The illustration shows pipe wor% with three openings 4 (4ase, C (Co""ector, and & (&!itter) The reservoir of water at ? is the supply voltage which is prevented from getting though to 8 by a plunger. If water is poured into 4" it pushes up the plunger letting lots of water flow from ? to 8. If even more water is poured into 4" the plunger moves higher" and the flow of water from ? to 8 increases. Therefore" a small input current of electricity to the 4ase leads to a large flow of electricity from the ?ollector to the 8mitter.
Transistor 6ain 7oo%ing at the water analogy again" if it ta%es 0 litre of water per minute poured into 4 to control 011 litres of water per minute flowing from ? to 8" then the 6ain !or a!p"i#ication #actor$ is 011. ( real transistor with a gain of 011 can control 011m( of current from ? to 8 with an input current of Bust 0m( to the base !4$. If the output power !current 6 voltage$ are more than 0 3att a Po:er Transistor must be used. These let much more power flow through" and re>uire a larger controlling input current.
DIOD&S ( diode is the simplest sort of semiconductor device. 4roadly spea%ing" a semiconductor is a material with a varying ability to conduct electrical current. ost semiconductors are made of a poor conductor that has had i!purities !atoms of another material$ added to it. The process of adding impurities is called dopin%.
S7M4OL OF DIOD&
Circuit Symbol
IMA6& OF DIOD&S
In the case of 789s" the conductor material is typically a"u!inu!?%a""iu!? arsenide !(lCa(s$. In pure aluminum-gallium-arsenide" all of the atoms
bond perfectly to their neighbors" leaving no free e"ectrons !negativelycharged particles$ to conduct electric current. In doped material" additional atoms change the balance" either adding free electrons or creating ho"es where electrons can go. 8ither of these additions ma%e the material more conductive. ( semiconductor with e6tra electrons is called N?t$pe !ateria" " since it has e6tra negatively-charged particles. In N-type material" free electrons move from a negatively-charged area to a positively charged area. ( semiconductor with e6tra holes is called P?t$pe !ateria"" since it effectively has e6tra positively-charged particles. 8lectrons can Bump from hole to hole" moving from a negatively-charged area to a positively-charged area. (s a result" the holes themselves appear to move from a positivelycharged area to a negatively-charged area. ( diode comprises a section of N-type material bonded to a section of /-type material" with electrodes on each end. This arrangement conducts electricity in only one direction. 3hen no voltage is applied to the diode" electrons from the N-type material fill holes from the /-type material along the =unction between the layers" forming a dep"etion one. In a depletion +one" the semiconductor material is returned to its original insu"atin% state -- all of the holes are filled" so there are no free electrons or empty spaces for electrons" and charge can@t flow.
At the junction, free electrons from the N-type material fill
holes from the P-type material This creates an insulatin! layer in the mi""le of the "io"e calle" the "epletion #one
To get rid of the depletion +one" you have to get electrons moving from the N-type area to the /-type area and holes moving in the reverse direction. To do this" you connect the N-type side of the diode to the negative end of a circuit and the /-type side to the positive end. The free electrons in the Ntype material are repelled by the negative electrode and drawn to the positive electrode. The holes in the /-type material move the other way. 3hen the voltage difference between the electrodes is high enough" the electrons in the depletion +one are boosted out of their holes and begin moving freely again. The depletion +one disappears" and charge moves across the diode.
When the ne!ati$e en" of the circuit is hoo%e" up to the N-type layer an" the positi$e en" is hoo%e" up to P-type layer, electrons an" holes start mo$in! an" the "epletion #one "isappears
If you try to run current the other way" with the /-type side connected to the negative end of the circuit and the N-type side connected to the positive end" current will not flow. The negative electrons in the N-type material are attracted to the positive electrode. The positive holes in the /-type material
are attracted to the negative electrode. No current flows across the Bunction because the holes and the electrons are each moving in the wrong direction. The depletion +one increases. !&ee *ow &emiconductors 3or% for more information on the entire process.$
When the positi$e en" of the circuit is hoo%e" up to the Ntype layer an" the ne!ati$e en" is hoo%e" up to the P-type layer, free electrons collect on one en" of the "io"e an" holes collect on the other The "epletion #one !ets &i!!er
DIOD&S CHARACT&RISTICS
L&D ( light-emitting diode !789$ is a semiconductor device that emits visible light when an electric current passes through it. The light is not particularly bright" but in most 789s it is monochromatic" occurring at a single wavelength. The output from an 789 can range from red !at a wavelength of appro6imately 11 nanometers$ to blue-violet !about ,11 nanometers$. &ome 789s emit infrared !I= $ energy !D:1 nanometers or longer$A such a device is %nown as an infrared-emitting diode !I=89$. (n 789 or I=89 consists of two elements of processed material called Ptype semiconductor s and N-type semiconductor s. These two elements are placed in direct contact" forming a region called the P-N junction. In this respect" the 789 or I=89 resembles most other diode types" but there are important differences. The 789 or I=89 has a transparent pac%age" allowing visible or I= energy to pass through. (lso" the 789 or I=89 has a large /N-Bunction area whose shape is tailored to the application.
S7M4OL OF L&D
Circuit Symbol
4ene#its o# L&Ds •
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Lo: po:er reBuire!ent ) ost types can be operated with battery power supplies. Hi%h e##icienc$ ost of the power supplied to an 789 or I=89 is converted into radiation in the desired form" with minimal heat production. Lon% "i#e 3hen properly installed" an 789 or I=89 can function for decades.
T$pica" App"ications •
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Indicator "i%hts These can be two-state !i.e." onoff$" bar-graph" or alphabetic-numeric readouts. LCD pane" ;ac@"i%htin% &peciali+ed white 789s are used in flat panel computer displays. Fi;er optic data trans!ission 8ase of modulation allows wide communications bandwidth with minimal noise" resulting in high speed and accuracy. Re!ote contro" ost home-entertainment 'remotes' use I=89s to transmit data to the main unit. optoiso"ator &tages in an electronic system can be connected together without unwanted interaction.
IMA6& OF DIFF&R&NT L&DS
4ATT&R7 (n electrochemical battery - or" more precisely" a 'cell' - is a device in which the reaction between two substances can be made to occur in such a way that some of the chemical energy is converted to useful electricity. 3hen the cell can only be used once" it is called a 'primary' cell. 3hen the chemical reaction can be reversed repeatedly by applying electrical energy to the cell" it is called a 'secondary' cell and can be used in an accumulator or 'storage' battery. ?ertain cells are capable of only a few charge-discharge cycles and are" therefore" technically 'secondary' cells. &uch is the case with certain silver o6ide-+inc batteries. These batteries are not capable of the repeated cycling re>uired of a satellite battery system" and are" therefore" considered to be 'rechargeable primary' rather than storage batteries.
S7M4OL OF 4ATT&R7
To define a battery in another way" it is an arrangement whereby an 'electrochemical' reaction can be made to ta%e place so that the 'electrical' part of the reaction proceeds via the metallic path of the e6ternal circuit" while the 'chemical' part of the reaction occurs via ionic conduction through electrolyte. The type of chemical reaction that can be used in an electrochemical cell is %nown as an 'o6idation-reduction' reaction - a reaction in which one chemical species gives electrons to another. 4y separating the two species and controlling the flow of ions between them" battery engineers ma%e devices in which essentially all of these electrons can be made to flow through an e6ternal circuit" thereby converting most of the chemical energy to electrical energy during the discharge of the cell.
So!e o# the co!ponents co!!on to a"" ce""s are
0. The 'cathode' or 'positive' electrode" which consists of a mass of 'electron-receptive' chemical held in intimate contact with a metallic 'plate' through which the electrons arrive from the e6ternal circuit. ;. The 'anode' or 'negative' electrode" which consists of another chemical which readily gives up electrons - an 'electron donor' similarly held in close contact with a metallic member through which electrons can be conducted to the e6ternal circuit. :. The 'electrolyte"' usually a li>uid solution that permits the transfer of mass necessary to the overall reaction. This movement ta%es place by 'migration' of 'ions' - positively or negatively charged molecular fragments - from anode to cathode and from cathode to anode.
( schematic diagram of these basic cell elements is shown above. The cell is shown connected to a load - representing the discharge reaction. ?harging is accomplished by connecting an electrical source in place of the load" thereby reversing the entire process
COND&NS&R MICROPHON& Condenser means capacitor " an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuc% as the name for this type of microphone" which uses a capacitor to convert acoustical energy into electrical energy. ?ondenser microphones re>uire power from a battery or e6ternal source. The resulting audio signal is stronger signal than that from a dynamic. ?ondensers also tend to be more sensitive and responsive than dynamics"
ma%ing them well-suited to capturing subtle nuances in a sound. They are not ideal for high-volume wor%" as their sensitivity ma%es them prone to distort.
Ho: Condenser Microphones Wor@ ( capacitor has two plates with a voltage between them. In the condenser mic" one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struc% by sound waves" changing the distance between the two plates and therefore changing the capacitance. &pecifically" when the plates are closer together" capacitance increases and a charge current occurs. 3hen the plates are further apart" capacitance decreases and a discharge current occurs. ( voltage is re>uired across the capacitor for this to wor%. This voltage is supplied either by a battery in the mic or by e6ternal phantom power . Cross-Section of a Typical Condenser Microphone
The &"ectret Condenser Microphone The electret condenser mic uses a special type of capacitor which has a permanent voltage built in during manufacture. This is somewhat li%e a permanent magnet" in that it doesn@t re>uire any e6ternal power for operation. *owever good electret condenders mics usually include a preamplifier which does still re>uire power. Other than this difference" you can thin% of an electret condenser microphone as being the same as a normal condenser.
Technical Notes: •
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?ondenser microphones have a flatter fre>uency response than dynamics. ( condenser mic wor%s in much the same way as an electrostatic tweeter !although obviously in reverse$. (dvantages) 4est overall fre>uency response ma%es this the microphone of choice for many recording applications. •
9isadvantages) 86pensive ay pop and crac% when close mi%ed •
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=e>uires a battery or e6ternal power supply to bias the plates.
SOLD&RIN6 T&CHNI'U&S
4ad solder Boints are often the cause of annoying intermittent faults. They can often be hard to find an cause circuit failure at the most inappropriate time. It’s much better to learn to ma%e a good solder Boints from day one. /reparing the soldering iron)
3ipe the tip clean on the wetted sponge provided.
4ring the resin cored solder to the iron and ‘tin’ the tip of the iron.
3ipe the e6cess solder of the tip using the wet sponge.
=epeat until the tip is properly ‘tinned’.
SOLD&RIN6 COMPON&NTS INTO TH& PC4
4end the component leads at right angles with both bends at the same
distance apart as the /?4 pad holes.
8nsure that both component leads and the copper /?4 pads are clean and free of o6idi+ation.
Insert component leads into holes and bend leads at about :1 degrees from vertical.
5sing small angle cutters" cut the leads at about 1.0 - 1.; of an inch !about ; - , mm$ above copper pad.
4ring tinned soldering iron tip into contact with both the component lead and the /?4 pad. This ensures that both surfaces undergo the same temperature rise.
4ring resin cored solder in contact with the lead and the copper
pad. Feed Bust enough solder to flow freely over the pad and the lead without a ‘blobbing’ effect. The final solder Boint should be shiny and concave indicating good ‘wetting’ of both the copper pad and the component lead. If a crac% appears at the solder to metal interface then the potential for forming a dry Boint e6ists. If an unsatisfactory Boint is formed" suc% all the solder off the Boint using a solder suc%er or solder wic% !braid$ and start again.
PR&CAUTIONS 0.
ount the components at the approp places before soldering. Follow the circuit discription and components details" leads identification etc. 9o not start soldering before ma%ing it confirm that all the components are mounted at the right place.
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9o not use a spread solder on the board" it may cause short circuit.
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9o not sit under the fan while soldering.
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/osition the board so that gravity tends to %eep the solder where you want it.
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9o not over heat the components at the board. 86cess heat may damage the components or board.
E.
The board should not vibrate while soldering otherwise you have a dry or a cold Boint.
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9o not put the %it under or over voltage source. 4e sire about the voltage either is d.c. or a.c. while operating the gadget.
D.
9o spare the bare ends of the components leads otherwise it may short circuit with the other components. To prevent this use sleeves at the component leads or use sleeved wire for connections.
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9o not use old dar% colour solder. It may give dry Boint. 4e sure that all the Boints are clean and well shiny.
01.
9o ma%e loose wire connections specially with cell holder" spea%er" probes etc. /ut %nots while connections to the circuit board" otherwise it may get loose.
