Super simple stepper motor controller


The circuit shown above can be used to control a unipolar stepper motor which has FOUR coils (I've swiped it off an old fax machine). The above circuit can be for a motor current of up to about 500mA per winding with suitable heat sinks for the SL100. For higher currents power transistors like 2N3055 can be used as darlington pair along with SL100. The diodes are used to protect the transistor from transients.

Activating sequence:-

Inputs

D0 D1 Coils Energised

0 0 A,B

0 1 B,C

1 0 C,D

1 1 D,A

To reverse the motor just reverse the above sequence viz. 11,10,01,00.

Alternately a 2bit UP/DOWN counter can also be used to control the direction , and a 555 multi-vibrator can be used to control the speed

Discrete component motor direction controller



This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF. When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the motor is more positive than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s ,but the ones I used had a very low hFE ~70 and they would enter the active region for 3V(2.9V was what I got from the computer for a HIGH),so I had to use the BC148s . You can ditch the BC148 if you have a SL/SK100 with a decent value of hFE ( like 150).The diodes protect the transistors from surge produced due to the sudden reversal of the motor.

Automatic Speed Controller for fans & Coolers




During summer nights, the temperature is initially quite high. As time passes, the temperature starts dropping. Also, after a person falls asleep, the metabolic rate of ones body decreases. Thus, initially the fan/cooler needs to be run at full speed. As time passes, one has to get up again and again to adjust the speed of the fan or the cooler.The device presented here makes the fan run at full speed for a predetermined time. The speed is decreased to medium after some time, and to slow later on. After a period of about eight hours, the fan/cooler is switched off.Fig. 1 shows the circuit diagram of the system. IC1 (555) is used as an astable multivibrator to generate clock pulses. The pulses are fed to decade dividers/counters formed by IC2 and IC3. These ICs act as divide-by-10 and divide-by-9 counters, respectively. The values of capacitor C1 and resistors R1 and R2 are so adjusted that the final output of IC3 goes high after about eight hours.The first two outputs of IC3 (Q0 and Q1) are connected (ORed) via diodes D1 and D2 to the base of transistor T1. Initially output Q0 is high and therefore relay RL1 is energised. It remains energised when Q1 becomes high. The method of connecting the gadget to the fan/cooler is given in Figs 3 and 4.








It can be seen that initially the fan shall get AC supply directly, and so it shall run at top speed. When output Q2 becomes high and Q1 becomes low, relay RL1 is turned off and relay RL2 is switched on. The fan gets AC through a resistance and its speed drops to medium. This continues until output Q4 is high. When Q4 goes low and Q5 goes high, relay RL2 is switched off and relay RL3 is activated. The fan now runs at low speed.Throughout the process, pin 11 of the IC is low, so T4 is cut off, thus keeping T5 in saturation and RL4 on. At the end of the cycle, when pin 11 (Q9) becomes high, T4 gets saturated and T5 is cut off. RL4 is switched off, thus switching off the fan/cooler.Using the circuit described above, the fan shall run at high speed for a comparatively lesser time when either of Q0 or Q1 output is high. At medium speed, it will run for a moderate time period when any of three outputs Q2 through Q4 is high, while at low speed, it will run for a much longer time period when any of the four outputs Q5 through Q8 is high.If one wishes, one can make the fan run at the three speeds for an equal amount of time by connecting three decimal decoded outputs of IC3 to each of the transistors T1 to T3. One can also get more than three speeds by using an additional relay, transistor, and associated components, and connecting one or more outputs of IC3 to it.
In the motors used in certain coolers there are separate windings for separate speeds. Such coolers do not use a rheostat type speed regulator. The method of connection of this device to such coolers is given in Fig. 4.
The resistors in Figs 2 and 3 are the tapped resistors, similar to those used in manually controlled fan-speed regulators. Alternatively, wire-wound resistors of suitable wattage and resistance can be used.

Compiler Hex code file to be directly programmed into the PIC

:10000000830100308A0004280C308400113016204F
:10001000830103309600FD309500113084001430C8
:100020001A208301102B04068001840A0406031998
:1000300000341328940024208000840A0408140645
:10004000031900341B289500961B2D2816088A00DA
:100050001508950A0319960A820083131618831748
:0A0060001508950A84000008080046
:1005F6008D018E0183128101082BC8300102031C74
:10060600082B81018D0A03198E0A00300E02623012
:1006160003190D0203180800002B8B131F308316D5
:1006260085008601D730810083128601B4232723F3
:100636000C081106031D212B7B231A2B0C0812060E
:10064600031D1A2B42231A2B8C018D018E01831256
:10065600810105183E2BC8300102031C2C2B810199
:100666008D0A03198E0A00300E02623003190D023C
:10067600031808002C2B05183E2B8C0A282B8F01FB
:10068600742B831227238C080319732B5A2B0610FD
:10069600732B8610732B0611732B8611732B061280
:1006A600732B8612732B0613732B8613732B0C086E
:1006B600940001309402031C732B083014020318B3
:1006C600732B03308A006B30140703188A0A8200E2
:1006D6004A2B4C2B4E2B502B522B542B562B582B34
:1006E6008F0A13080F02031C442B8C018312080087
:1006F6008F01AD2B831227238C080319AC2B932B68
:100706000614AC2B8614AC2B0615AC2B8615AC2B1D
:100716000616AC2B8616AC2B0617AC2B8617AC2B05
:100726000C08940001309402031CAC2B0830140210
:100736000318AC2B03308A00A430140703188A0A66
:100746008200832B852B872B892B8B2B8D2B8F2B35
:10075600912B8F0A13080F02031C7D2B8C01831229
:10076600080083120508183994000310940C03102E
:10077600940C0310140C8F0005080639940003101E
:10078600140C9000D72B023091000330D52B033088
:1007960091000430D52B043091000530D52B05305F
:1007A600910006309200F02B0F080319C62B013A70
:1007B6000319CA2B033A0319CE2B013A0319D22B7C
:1007C600F02B9301930A08000230930008000330CF
:1007D6009300080004309300080010080319E42B66
:1007E600013A0319E72B033A0319EA2B013A031DD1
:0A07F6000800ED2B04340534023432
:02400E00F13F80
:00000001FF

Parts list:

Parts list:


ICs:

IC1- PIC16F84A microcontroller
IC2- MCT2E opto isolator
IC3- NE555 timer Ic
IC5- 7805C or 7805CT regulator IC

Resistors (all 1/4th W unless otherwise stated):

R1- 10K, 1W
R2- 15K
R3 to R6 - 2.2K
R7 - 2.2K (eight pieces for eight relay circuits)


Capacitors:

C1- 0.47uF/200V non electrolytic
C2- 47uF/25V electrolytic
C3,C4 - 22pF non electrolytic
C5- 0.01uF non electrolytic
C7,C8 - 0.1 uF non electrolytic
C9,C10- 100uF/25V electrolytic


Transistors:

BC547 - eight pieces


Relays:

12V, 60mA (or less) relay with 2A SPDT switching contacts - 8 pieces


DIP switch:

4 switch DIP


Diodes:

D1,D2 - 10V, 500mW zener diodes
D3 - 1N4007
D4 - 1N4007 (8 pieces for 8 relay circuits)

Crystal:

Q1 - 4MHz ceramic crystal resonator

C source code complied using HT-Soft PIC C compiler

#define TIMEOUTS 98 // no. of timeouts to occur for waiting (1 timeout = 200x256us), 98 timeouts=5sec

#include

#include

__CONFIG(0x3ff1);

void ringcounter(void);

void dowakeon(void);

void dowakeoff(void);

void delay(void);

void wait5sec(void);

void getdipswitch(void);

char WAKEON = 4;

char WAKEOFF = 5;

char WAITDELAY = 2;

char ringcount=0;

unsigned int x=0;

void main(void)

{

GIE=0; //disable interrupts

TRISA=0b00011111; //PORTA=in

TRISB=0b00000000; //B0 to B7 output

OPTION=0b11010111; // tmr0/prescaler 256/tmr0 --> internal

PORTB =0; //turn all relays off

// getdipswitch function sets the intial on/off rings and also the delay for rings to turn device on through A4,A3,A2,A1

// A4 A3 wakeon wakeoff

// 0 0 2 3

// 0 1 3 4

// 1 0 4 5

// 1 1 5 6

//

// A2 A1 waitdelay

// 0 0 5

// 0 1 10

// 1 0 15

// 1 1 20

getdipswitch(); //configure rings and delay

while(1)

{

ringcounter();

if(ringcount==WAKEON)

dowakeon();

else if(ringcount==WAKEOFF)

dowakeoff();

}

}

void ringcounter(void)

{

ringcount=0;

while(1)

{

x=0;

TMR0=0;

while(RA0==0)

{

if(TMR0>=200) // to keep some margin in case TMR0 rolls back to 00, keep it to C8(200dec)!!

{

TMR0=0;

x++;

if(x>=TIMEOUTS) //if timeout 5s return. Total timeout = 200us*TIMEOUTS*256(prescaler)

return;

}

}

while(RA0==1); //while A0=1 wait

ringcount++;

}

}

void dowakeon(void)

{

char i;

for(i=0;i

{

ringcounter();

if(ringcount==0)

continue;

else

switch(ringcount)

{

case 1: RB0=1;

break;

case 2: RB1=1;

break;

case 3: RB2=1;

break;

case 4: RB3=1;

break;

case 5: RB4=1;

break;

case 6: RB5=1;

break;

case 7: RB6=1;

break;

case 8: RB7=1;

break;

default: break;

}

}

ringcount=0;

}

void dowakeoff(void)

{

char i;

for(i=0;i

{

ringcounter();

if(ringcount==0)

continue;

else

switch(ringcount)

{

case 1: RB0=0;

break;

case 2: RB1=0;

break;

case 3: RB2=0;

break;

case 4: RB3=0;

break;

case 5: RB4=0;

break;

case 6: RB5=0;

break;

case 7: RB6=0;

break;

case 8: RB7=0;

break;

default: break;

}

}

ringcount=0;

}

void wait5sec(void)

{

x=0;

TMR0=0;

while(x

if(TMR0>=200) // to keep some margin in case TMR0 rolls back to 00, keep it to C8(200dec)!!

{

TMR0=0;

x++;

}

return;

}

void getdipswitch(void)

{

char temp1,temp2;

temp1 = (PORTA&0b00011000)>>3; //get the A4,A3 bits into temp1

temp2 = (PORTA&0b00000110)>>1; //get the A2,A1 bits into temp2

switch(temp1)

{

case 0: WAKEON=2;WAKEOFF=3;

break;

case 1: WAKEON=3;WAKEOFF=4;

break;

case 2: WAKEON=4;WAKEOFF=5;

break;

case 3: WAKEON=5;WAKEOFF=6;

break;

default:break;

}

switch(temp2)

{

case 0: WAITDELAY=1;

break;

case 1: WAITDELAY=2;

break;

case 2: WAITDELAY=3;

break;

case 3: WAITDELAY=4;

break;

default:break;

}

}

Circuit : Telephone operated remote control using PIC16F84A microcontroller



Circuit : Telephone operated remote control using PIC16F84A microcontroller

Telephone operated remote control using PIC16F84A microcontroller

This design controls up to 8 devices using a PIC microcontroller (PIC16F84A) connected to the phone line. The unique feature here is that unlike other telephone line based remote control, this device does not need the call to be answered at the remote end so the call will not be charged. This device depends on number of rings given on the telephone line to activate/deactivate devices.

Instructions for the telephone operated remote switch:

A) While constructing the main circuit, make sure you use 18pin sockets (base) for the PIC16F84A. Do not solder the IC directly to the board since you may have to remove it for programming. Before you use the PIC on the main circuit, you have to first program it.

B) To program the PIC16F84A microcontroller:

There are lots of programmers on the Internet available to program PIC microncontrollers. Given below are links to some free PIC programmer hardware/software:

  • http://www.covingtoninnovations.com/noppp/
  • http://www.picallw.com/
  • http://www.lpilsley.uklinux.net/software.htm

Note: Programm the chip with the hex file attached above and remember to set the fuse bits to use "EXTERNAL HS OSCILLATOR" mode!

C) Remove the PIC from the programmer socket and put it into the main circuit socket.

Set the DIP SWITCH as follows:

Switch3 Switch4 No. of initial rings to Switch ON(activate half of the board)

OFF OFF 5

ON OFF 4

OFF ON 3

ON ON 2

The number of initial rings to Switch OFF is one more than the number of rings to switch ON. For example, if you have set switch3 OFF & Switch4 ON then number of initial rings to activate half of the board to switch ON the relays is 3 and number of initial rings to activate half of the board to switch OFF the relays is 3+1 = 4

Switch1 Swtich2 Delay before making the second set of rings

OFF OFF 20sec

ON OFF 15sec

OFF ON 10sec

ON ON 5sec

This is the maximum delay the board can take after it is half activated. It will reset after this delay.

D) Now connect the circuit to the phone line and switch on its power supply.

E) You can test the board now. For example set the DIP switch to Switch1 ON, Switch2 OFF (15 sec delay) & switch3 ON, switch4 OFF (4 rings to activate half for switching ON). If you want to switch ON relay 1 (connected to RB0 of main circuit) then you have to do the following:

  1. Give 4 rings and put down the receiver
  2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
  3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
  4. then within 5 sec the relay1 will switch ON

To switch off relay1:

  1. Give 5 rings and put down the receiver
  2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
  3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
  4. then within 5 sec the relay1 will switch OFF

Dew sensor




Dew (condensed moisture) ad- versely affects the normal per- formance of sensitive electronic devices. A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity. At the heart of the circuit is an inexpensive (resistor type) dew sensor element.

Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorised service centres of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype.

In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project. The circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator. (Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal.

The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energised. At the same time LED1 provides a visual indication.

The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

Magnetic proximity sensors




Here is an interesting circuit for a magnetic proximity switch which can be used in various applications.
The magnetic proximity switch circuit, in principle, consists of a reed switch at its heart. When a magnet is brought in the vicinity of the sensor (reed switch), it operates and controls the rest of the switching circuit. In place of the reed switch, one may, as well, use a general-purpose electromagnetic reed relay (by making use of the reed switch contacts) as the sensor, if required. These tiny reed relays are easily available as they are widely used in telecom products. The reed switch or relay to be used with this circuit should be the normally open type.

When a magnet is brought/placed in the vicinity of the sensor element for a moment, the contacts of the reed switch close to trigger timer IC1 wired in monostable mode. As a consequence its output at pin 3 goes high for a short duration and supplies clock to the clock input (pin 3) of IC2 (CD4013 dual D-type flip-flop). LED D2 is used as a response indicator.
This CMOS IC2 consists of two independent flip-flops though here only one is used. Note that the flip-flop is wired in toggle mode with data input (pin 5) connected to the Q (pin 2) output. On receipt of clock pulse, the Q output changes from low to high state and due to this the relay driver transistor T1 gets forward-biased. As a result the relay RL1 is energised.

Chapter 3: Inductor

Let me be very brief here. The main purpose of this tutorial is to explain what an inductor is and how it behaves in an electronic circuit.

The definition of inductance goes like this:

"Inductance is the ability of a coil to establish (or induce) a voltage within itself to oppose changes in current through its windings".

That means when varying current flows through a coil, a voltage is induced within the coil in a direction so as to oppose the change of current through it.

The circuit symbol of an inductor is:

and like a resistor, it can be connected either way in a circuit, with the exception of mutually coupled coils that have to be connected in a particular way.

The unit of inductance:

The unit of inductance is 'henry' denoted by H. Usually, in electronics smaller values of H are used like mH (millihenry).

Applications of inductors:

One of the major applications come in from "mutually coupled" coils where the magnetic field established in one coil, 'cuts' through the other coil and hence induces a voltage in the other coil. This is called 'mutual inductance'. Such coils are widely used in transformers.

Transformers:

They are used in electronics to step-up or step-down voltages using mutually coupled coils. When a varying voltage(like AC) is applied to one of the coils of the transformer(called the Primary winding), a voltage is 'induced' in the other coil due to mutual inductance. The second coil in which the voltage is induced is called the Secondary winding.

If by applying a higher voltage to the primary, a lower voltage is obtained at the secondary, then the transformer is called a "Step-Down" transformer. If a lower voltage produces a higher voltage then its called a Step-Up transformer.

If the transformer produces a higher voltage from a lower or vice-versa, then isn't it defying the law of energy conservation? Well, not really. We are till now looking only at the voltages and not currents. Remember that energy(per time period) is the product of voltage AND current. What really happens in a transformer is, if it produces a higher voltage form a lower, then the output current will be lower than the input, thus maintaining the total energy constant.

The circuit symbol of a transformer is:

Primary Secondary

The "extra" wire in the middle of secondary is called the "center tap" which may or may not be present in all the transformers.

Usually the voltages between the centre tap and the other two taps of the secondary are equal.

Transformers are specified by the following:

1. Primary and secondary voltages.
2. Current rating.

For example, a 230V / 12-0-12V and 1A transformer means, the primary voltage is 230V and secondary voltages are 12V,0V,12V of the 3 tappings and can supply a maximum of 1A (this is the root-mean-square,rms value) . If you want to 12V from the transformer, then you can use the center tap and either of the other 2 end terminals.
If you use the two extreme ends, then the output will be 24V.
If the transformer's secondary is of 9-0V, it means the transformer has a secondary of 2 tappings and the voltage measured between the 2 tappings is 9V.

Just remember that the output of a transformer is AC and cannot be used for normal circuits and have to be converted to DC using "diodes".

Where are these transformers used?

In your T.V , computer, tape recorder,VCR and just about every electronic gadget that operates on mains. This is because if the mains voltage is 230V(or 110V), the gadgets need much lower voltages than that, say like 6V , 9V etc. These lower voltages are obtained by using a "step-down" transformer.
What about step-up transformers? They are used in inverters, which provide AC power from a battery.


- Naveen P N
http://electronic-circuits-diagrams.com

Chapter 2: Capacitor

Capacitors in electronics are like storage tanks. They store charges. Basically a capacitor is made up of 2 parallel plates separated by a very small gap, but there are other ways of making a capacitor too. A capacitor has two terminals.

It is charged by applying a voltage across its terminals, and discharged by shorting the two terminals. When a capacitor is charged, a voltage develops across its terminals even when the charging source is removed. The voltage across the terminals of a capacitor is related to the amount of charge stored in it by the relation:

    Voltage = Charge/Capacitance

    or

    V = Q / C

Where C is the capacitance of the capacitor and is measured in a unit called 'farad', denoted by F. If 1V is developed across the terminals of a capacitor by the storage of 1C(coloumb) of charge then its capacitance is 1 F.

Usually a farad is a large value and for most of the applications the value is expressed in terms of microfarads, nanofarads or picofarads.

1 microfarad ( uF ) = 10e-6 or 1/1000000th of a farad.

1 nanofarad ( nF ) = 10e-9 farad OR 1/1000th of a mic

1 picofarad ( pF ) = 10e-12 farad

( in uF above, 'u' is the greek letter mu and not the english letter 'u' )

Types of capacitors:

There are many types of capacitors but the two main types are:

- non-electrolytic

- electrolytic

Non-Electrolytic capacitors are non-polarised, i.e they can be connected either way in a circuit without having to worry about + & -. The most common is the disc-type capacitor that we normally use in electronics. The other types are ceramic, mica etc. In almost all applications we use the disc-type capacitor which is brown in color and has the shape of a disc. Its value ranges between about a few pF to as high as 1uF. ( You also get non-polarised capacitors of higher values and such capacitors have 'NP' written on them indicating Non Polarised)

Electrolytic capacitors are polarised and they are supposed to be connected in a specific way in the circuit. Their + and - terminals have to coincide with that specified in the circuit. They are much bulkier than the non-electrolytic type and hence have to be avoided when possible. They are used only if very high capacitance values are needed. Also the electrolytic capacitors are not very stable regarding their value i.e. their values change slightly with the temperature and other physical parameters. The non-electrolytic capacitors are relatively stabler. Electrolytic capacitors are available usually 1uF and upwards upto about 4700uF!
They are much costlier than the non-electrolytic capacitors.
CAUTION: Connecting an electrolytic capacitor in the wrong polarity may lead to an explosion! ( electrically controlled firecrackers? )

Circuit Symbol:

The symbol used for electrolytic and non-electrolytic capacitors are different.

The symbol for non-electrolytic capacitor is:

where the dark lines indicate the two plates, and the thin lines represent the two terminals.

The symbol for electrolytic capacitor is:

The terminal marked as + is the positive (or +) terminal and the other (unmarked) terminal is the negative or - terminal. When + is not indicated, the terminal near the curved line is assumed to be negative. On the actual electrolytic package, the negative terminal is usually indicated by a black line with arrows pointing towards the negative terminal.

When you buy a capacitor at a store, you have to specify 3 things:

1) Electrolytic/ non-electrolytic.
2) Capacitance.
3) Max. tolerable voltage.

1) Electrolytic/non-electrolytic: This depends usually on the value of the capacitance. If its less then 1uF then go for non-electrolytic and for higher values use electrolytic.
2) As mentioned above, the value of a capacitor or its capacitance id specified in uF / nF / pF
3) All capacitors have a max. voltage specified and which is the max. voltage that can be applied across its terminals. If a higher voltage is applied, it may damage the capacitor.

The max. voltage for a non-electrolytic capacitor is usually a few hundred volts and is not specified in circuit diagrams since this voltage is much higher than the supply voltage of many electronic circuits.
For the electrolytic capacitors, the max. voltage is almost always specified in the circuit. If its not specified, assume it to be a little higher than the supply voltage to the circuit. For example if circuit operates at 12V then the electrolytic capacitors can be purchased with a max. voltage of about 16V.Note here that as the max. voltage increases the cost of the capacitor also increases.

How to read a capacitor's value?

Non-Electrolytic:
Some capacitors have their values printed in them. Unfortunately, there are various formats for printing the values and only a few can be discussed here:

1) If the printed value is like 101,102,103,204 etc then the value of the capacitor= (first 2 digits X 10 raised to the 3rd digit) pF.
For example if the value is 104 then capacitance = ( 10X 10e4) pF = 10e5 pF = 10e-7 F = 0.1uF
Remember a few of them: 104 = 0.1uF , 224=0.22uF , 103= 0.01uF, 102= 0.001uF

2) If the printed value is like 1K5, 100,220,10K etc,
Then capacitance = (printed value) pF
For example if the value is 10K then capacitance = 10K pF = 10X10e3 pF= 10e-8 F= 0.01uF
1K5 means 1.5K pF and so on.

Electrolytic:
Fortunately, both the capacitance and the max. voltage are both printed on the electrolytic in plain English!

There are a few capacitance available with color band coding like in the resistors, but their value is in pF and has to be multiplied by 10e-12 after de-coding the value.

Capacitors in Series and Parallel:

(Please read the chapter on resistors before proceeding)
This is very similar to the resistors except the formula for series and parallel connections are interchanged.
If Cab is the effective capacitance of a series or parallel combination then, it is given by.

1/Cab(series) = 1/C1 + 1/C2 + 1/C3 where C1,C2,C3 are individual capacitances.

Cab(parallel) = C1 + C2+ C3

Variable Capacitors(trimmers):

Variable capacitors are available only for very small values like pF and should be normally avoided. They, like variable resistors have three terminals for the same reasons as discussed in the chapter on resistors.

The main use of variable resistors are in the radio and are used for tuning.

The circuit symbol of variable capacitor is:

Applications of capacitors:

Capacitors are as indispensable as the resistor in electronics. You can find them in almost every electronic circuit. They are used mainly in delay circuits like timers, noise suppression(smoothing) , oscillators to name a few.

The capacitor is used to:
1. Block DC
2. Pass AC
3. Store charges.

Formulae to memorize:

1) V=Q/C

2) C(parallel)= C1+C2

3) C(series)= (C1*C2)/(C1+C2)



- Naveen P N

 
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