Electronic Circuits.

The Monostable 555 Timer

2011-10-12T03:36:00.000-07:00

The operation and output of the 555 Monostable is exactly the same as that for the transistorised one we look at previously in the Monostable Multivibrators tutorial. The difference this time is that the two transistors have been replaced by the 555 timer device. Consider the 555 Monostable circuit below.

When a negative (0V) pulse is applied to the trigger input (pin 2) of the Monostable configured 555 Timer oscillator, the internal comparator, (comparator No1) detects this input and "sets" the state of the flip-flop, changing the output from a "LOW" state to a "HIGH" state. This action inturn turns "OFF" the discharge transistor connected to pin 7, thereby removing the short circuit across the external timing capacitor, C1. This allows the timing capacitor to start to charge up through resistor, R1 until the voltage across the capacitor reaches the threshold (pin 6) voltage of 2/3Vcc set up by the internal voltage divider network. At this point the comparators output goes "HIGH" and "resets" the flip-flop back to its original state which inturn turns "ON" the transistor and discharges the capacitor to ground through pin 7. This action also causes the output to change its state back to the original stable "LOW" value awaiting another trigger pulse to start the timing process over again. Then as before, the Monostable Multivibrator has only ONE stable state.

The Monostable 555 Timer circuit triggers on a negative-going pulse applied to pin 2 and this trigger pulse must be much shorter than the output pulse width allowing time for the timing capacitor to charge and then discharge fully. Once triggered, the 555 Monostable will remain in this "HIGH" unstable output state until the time period set up by the R₁.C₁ network has elapsed. The amount of time that the output voltage remains "HIGH" or at a logic "1" level, is given by the following time constant equation.

Where, t is in seconds, R is in Ω's and C in Farads.

LM3915/LM3916 VU Meter

2011-07-29T01:48:00.000-07:00

Features

Fast responding electronic VU meter

Drivers LEDs, LCDs, or vacuum fluorescents

Bar or dot display mode externally selectable by user

Expandable to displays of 70 dB

Internal voltage reference from 1.2V to 12V

Operates with single supply of 3V to 25V

Inputs operate down to ground

Output current programmable from 1 mA to 30 mA

Input withstands ±35V without damage or false outputs

Outputs are current regulated, open collectors

Directly drives TTL or CMOS

The internal 10-step divider is floating and can be referenced to a wide range of voltages The LM3916 is rated for operation from 0°C to +70°C. The LM3916N-1 is available in an 18-lead molded DIP package.

Description
The LM3916 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, LCDs or vacuum fluorescent displays, providing an electronic version of the popular VU meter. One pin changes the display from a bar graph to a moving dot display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The whole display system can operate from a single supply as low as 3V or as high as 25V.
The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 0.2 dB.
Audio applications include average or peak level indicators, and power meters. Replacing conventional meters with an LED bar graph results in a faster responding, more rugged display with high visibility that retains the ease of interpretation of an analog display.
The LM3916 is extremely easy to apply. A 1.2V full-scale meter requires only one resistor in addition to the ten LEDs. One more resistor programs the full-scale anywhere from 1.2V to 12V independent of supply voltage. LED brightness is easily controlled with a single pot.

Stereo FM/AM Receiver CXA1538

2011-04-04T03:10:00.000-07:00

Description Of Stereo FM/AM Receiver CXA1538

The CXA1538M/N/S is high performance one-chip bipolar ICs designed for FM stereo/AM radios. These include an FM/AM front end, FM/AM IF amplifier, FM/AM detection output and FM stereo demodulator output. Pin 4 is the stereo indicator and VCO check pin. Therefore, in stereo mode (when stereo indicator drive Tr Q2 is switched on), pin 4 voltage lowers down, Q1 is cut off and VCO oscillation waveform can not be seen. In AM mode as well, the oscillation waveform can not be seen as VCO turns off.

Adjust the free run frequency at 76 kHz ±50 Hz. This IC has a built-in auto blend circuit and a MONO switch is not required as a rule. This circuit controls the separation in proportion to the signal level and reduces noise automatically for stereo reception below the mid electric field when the electric field strength reaches lower than about 40 dBμ. When the electric field strength turns below 10 to 15 dBμ, MONO operation is automatically activated. To switch MONO mode on externally, ground pin 3 with 33 Kohm. This IC has a built-in soft muting circuit. As shown in the following I/O characteristics diagram, 23 dB (Typ.) muting is applied and noise level reduced during weak electric field and out of tune instances.

Features Of Stereo FM/AM Receiver CXA1538

Low current consumption (In FM mode ID=11.0 mA, in AM mode 8.5 mA, VCC=6.0 V)
Built-in LED drive circuit for tuning
Built-in LED drive circuit for stereo indicator
Built-in muting circuit for the FM band
Few external parts

AUDIO POWER METER circuit WITH LM3915

2011-04-04T01:12:00.000-07:00

This VU (volume-unit) meter is capable of monitoring and displaying

power levels present at the speaker terminals of a stereo audio

power amplifier.

The levels are displayed in ten discrete steps. This meter is not

designed to give an accurate display of the power levels.It is

designed to give an approximate visual indication of the audio

power output of each channel. For many situations - disco, parties this

is all which is required: the flashing LED's add atmosphere to the

situation.

LM3915. This is a monolithic Dot/Bar Display Driver IC made by

National Semiconductor. It takes an analog voltage input on pin 5

then drives 10 LED's providing a logarithmic 3dB/step analog display.

When measuring power, a 3dB increase means that the power input

has doubled. As the power doubles, an additional LED will be lit until

the maximum is reached. The display can be bar or moving dot

depending on the connection of pin 9 to the positive supply. The LED

drive current is regulated which eliminates the need for current

limiting resistors.

The supply voltage can be between 3V to 25V.

Mini Audio Spectrum Analyzer LM3915

2011-04-04T01:04:00.000-07:00

The circuit has been designed to create a spectrum analyzer that will provide an analysis of

a sound to determine at various frequencies, the volume of sounds that make up the overall

sound spectrum.

Circuit Explanation

The device is sensitive enough to determine the sound wave components of frequency and

amplitude with the changing of frequency and the width of an acoustic signal. The

proportionality of signal width is indicated by the brightness of LED as it turns ON while the

color indicates the proportionality of frequency. In order for the red LED to turn ON in strong

signal, the sensitivity of the input circuit is adjusted by resistor R2. The middle signal is

represented by a yellow LED while the low signal is indicated the green LED.

The 10 LEDs in 3 lines comprise the display unit which is ensured the IC2 as it functions as

a counter decoder represented by the two gates ICa-b.the frequency of the counter is being

regulated by R6. No LED will turn ON in the absence of any signal in the input. The LEDs will

begin to flicker or blink depending on the intensity and tempo of the signal, once a signal

has been applied in the input. The values of the resistors R4 & R5 can be varied that will be

suitable for the desired requirements. Alternatively, this can be done by placing a 1K ohm

trimmer in place of R4 & R5 during the initial regulation and adjustment of the values. It can

be eventually removed and replaced with permanent resistors as soon as the desired

values are achieved. Additional LEDs can be added in connection to IC2 although this

circuit does not precisely measure the input signal.

Part List

R1= 1K8Kohm

R2= 100Kohm trimmer

R3= 1Kohm

R4= 100 ohm…..1Kohm

R5= 100 ohm…..1Kohm

R6= 100Kohm trimmer

C1= 100nF 100V

D1….10= RED LED

D11….20= YELLOW LED

D21….30= GREEN LED

IC1= LM3915

Controlling LED brightness using PWM

2011-03-30T20:45:00.000-07:00

Pulse Width Modulation or PWM is a term you hear a lot if you are interested in controlling power output using a microcontroller. It has many applications, although one of the most popular amongst hobbyists is controlling the brightness of LEDs. In this tutorial we will cover the basic principles behind PWM and how it can be used for LED brightness control including fading out LEDs rather than just turning them on and off.

This article will focus on some of the more specific details of the PIC18F range of microcontrollers; however the techniques and principles are the same for all other microcontroller products. Some microcontrollers include PWM modules which perform all of the hard work for you; however this article focuses on the more universal (and scalable) technique of using interrupts.

Introduction

To control the brightness of an LED you can vary the power which is sent to the LED, for example using a potentiometer (variable resistor), the more power the LED receives the brighter it is, the less power it receives the dimmer it is. Microcontrollers are digital, meaning they only have two ‘power’ states, on and off. Although it is possible to supply a varying power from a microcontroller (using a Digital to Analogue Convertor (DAC)) this usually requires an additional chip. PWM provides the ability to ‘simulate’ varying levels of power by oscillating the output from the microcontroller.

If, over a short duration of time, we turn the LED on for 50% and off for 50%, the LED will appear half as bright since the total light output over the time duration is only half as much as 100% on. The important factor here is the ‘duration’, if we turn the light on and off too slowly the viewer will see the flashing of the LED not a constant light output which appears dimmer. The pulsing width (in this case 50%) is the important factor here. By varying (or ‘modulating’) the pulsing width we can effectively control the light output from the LED, hence the term PWM or Pulse Width Modulation.

When using PWM it’s important to consider how slowly we can ‘flash’ the LED so that the viewer does not perceive the oscillation. The eye’s inability to see rapid oscillations of light is caused by our ‘persistence of vision’ which means, in very simple terms, we see the light as on even after it has turned off. This technique is how televisions display a seemingly moving picture which is actually made up of a number of different still frames displayed one after the other very rapidly. The minimum speed of an LED oscillating which can be seen by the human eye varies from person to person. However, for the purposes of this article, we will use a minimum speed of 50Hz, or 50 times per second.

Duty-Cycle

When using PWM there are certain terms which you will come across again and again. The most important term is ‘duty-cycle’. The duty-cycle refers to the total amount of time a pulse is ‘on’ over the duration of the cycle, so at 50% brightness the duty-cycle of the LED is 50%. The ‘cycle’ itself is measured (usually) in Hertz which gives us the cycles-per-second. So at 50Hz our cycle is 1 second divided by 50 cycles, which is 0.02 seconds. Since we are using such small time measurements it’s more useful to use microseconds (there are 1,000,000 microseconds in a second), this gives us a cycle duration of 20,000 microseconds which is 50 cycles per second or 50Hz.

During the 20,000 microseconds we have to turn the LED either on or off depending on the required duty-cycle so, for example, a 75% duty-cycle requires the pulse to be on for 15,000 microseconds and then off for 5,000 microseconds.

PWM Resolution

The accuracy with which we can control the duty-cycle is known as the ‘PWM resolution’. The higher our PWM resolution is, the more levels of ‘brightness’ we can display. However, since the duty-cycle is ‘fixed’ at 50Hz more resolution requires finer timing from the microcontroller. The faster the microcontroller, the smaller durations it can time. Another limiting factor is the code execution, the microcontroller must not only time the ‘interrupt’ which causes the pulse generation, but also run the code which controls the LED output, which must complete before the next interrupt is called. In addition, you probably want your microcontroller to be performing tasks other than LED PWM brightness control, so there has to be some spare execution time between interrupts to do all of the other more general processing tasks.

With PWM control of LEDs the primary advantage of higher PWM resolutions is that it results in a smaller difference between ‘off’ and the lowest possible brightness from the LED. For example if our duty-cycle is 20,000 microseconds (50Hz) and our resolution is only 10,000 microseconds, the difference between ‘off’ and the lowest possible brightness will be 50% of the total possible brightness. At a resolution of 2,000 microseconds the difference would be 10% and so on. Overall the ‘PWM resolution’ dictates the number of brightness ‘levels’ we can support between completely off (0%) and completely on (100%). Again, the higher the resolution, the more timing accuracy and processing overhead is required.

For your application the required resolution and overall duty-cycle may vary. Simple displays require very little precision control (and sometimes a little flickering is not the end of the world), for more advanced displays the ability to control levels of brightness might be critical (think of the issue of mixing colours using a RGB LED for example). The trade-off is simple, more control and accuracy requires more and more microcontroller resources. In this article we will focus on an example which supplies a resolution of 1,000 microseconds over a 20,000 microsecond duty-cycle (or 50Hz with steps of 5% giving us 20 levels of brightness). This level of control and accuracy is suitable for many purposes.

Timing the Interrupt

To perform the PWM using an interrupt we have to call the interrupt once every 1,000 microseconds and decide if the LED should be on or off. To do this we have to set up a timer on the microcontroller which calls the interrupt when it expires.

For this example we will take a Microchip PIC18F4550 microcontroller running at 48Mhz as the example. 48Mhz means the clock of the microcontroller will ‘tick’ 48,000,000 times a second. This is referred to as ‘Fosc’ (the Frequency of oscillation). A PIC18F4550 requires 4 ticks of the clock to process a single instruction. This means the smallest amount of time we can deal with using the microcontroller is a quarter of the clock rate, i.e. 48,000,000 / 4 = 12,000,000 (this is also known as Fosc/4), if there are 1,000,000 microseconds in a second, this means we execute a command around once every 0.0834 microseconds (12 MIPS (Million Instructions Per Second)). Although this is not quite correct in PWM terms since to generate a pulse we would need two commands (on and off) meaning a minimum cycle time of 0.167 microseconds (this effectively limits the highest frequency we can produce in software to 6Mhz, although this is not a very practical maximum).

If the Fosc/4 rate is 12,000,000 this means 1 microsecond of time passes for every 12 processor cycles. This means that 1,000 microseconds is equivalent to 12,000 processor cycles. This is important because with a 1:1 prescaler the PIC’s timers update once every processor cycle (although this is referred to as a 1:1 prescale, it really means no prescale at all). The timer’s prescaler slows down the rate at which the timer’s counter updates, with a 1:2 prescaler it updates once every 2 processor cycles, with a 1:4 prescaler it updates once every 4 processor cycles and so on.

To use an 8-bit timer (you can use a 16-bit timer also if you like) the maximum period the timer can measure is 256 ‘counts’ (0-255). Therefore we have to pick a prescaler value which allows us to time 12,000 processor cycles in less than 256 timer ticks. If we use a 1:64 prescaler we require 187.5 timer ticks to measure 1,000 microseconds:

12 processor cycles per microsecond, so 12 * 1000 = 12,000 processor cycles per 1,000 microseconds: 12,000 cycles / 64 (prescale) = 187.5 timer ‘ticks’

Since we cannot count a ‘half’ we simply round the figure down to the nearest integer (this means are resulting PWM will not be totally accurate, but for the purpose of controlling LED brightness this is not very critical). The higher prescale value we use, the less accurate the timing becomes. This can be corrected by using a 16-bit timer which allows us to count far more ticks and therefore use a lower prescale value.

For a PIC18F4550 this will result in code similar to the following excerpt where the timer0 module is configured, enabled and set to generate a low-priority interrupt:

// Enable interrupts with priority
 IPEN = 1;
 
 // Set up timer0
 TMR0IP = 0;   // Set timer0 interrupt to low priority
 TMR0IF = 0;   // Clear the timer0 interrupt flag
 TMR0L = 255 - 187;  // Reset the timer0 counter
 
 T0CON = 0b11000101;  // Timer0 on, 8-bit and 1:64 prescaler
 TMR0IE = 1;   // Enable the timer0 interrupt
 
 // Enable interrupts
 GIEH = 1;   // Global enable all high priority interrupts
 GIEL = 1;   // Global enable all low priority interrupts

Once the timer is configured and running we need some interrupt code to decide if the LED should be on or off for the interrupt. Since we have 20 possible brightness levels (and therefore 20 steps of resolution in our PWM generation) we can simply use a counter which counts from 0-19 and is updated once every interrupt. If the brightness of the LED is represented using a number from 0-19 we simply have to check if the PWM counter is higher or lower than the brightness number to see if the LED should be on or off.

// Globals for PWM
unsigned char pwmCounter = 0;
unsigned char ledBrightness = 0;
 
// Low priority interrupt procedure
void interrupt low_priority lpHandler(void)
{
 // Is this timer0 interrupting?
 if (TMR0IF)
 {
  if (ledBrightness > pwmCounter)
   LED0 = 1; else LED0 = 0;
 
  pwmCounter++;
  if (pwmCounter > 19)
   pwmCounter = 0;
 
  // Get ready for the next interrupt
  TMR0L = 255 - 187; // Reset the timer0 counter
  TMR0IF = 0;  // Clear the timer0 interrupt flag
 }
}

Fading the LED

Since we know the cycle duration of the timer0 timer we can also use this to provide fading effects on the LED. To do this we have to store two values for the LED brightness, one variable to store the actual displayed brightness and another to store the target brightness for the LED. Since we only want fade off (you could adapt this easily to support both fade on and fade off) if the target brightness is higher than the actual brightness, we immediately bring the actual brightness to the same level.

However, for fading off we want to decrement the actual brightness level one step at a time until it equals the target brightness. Since there are only 20 levels of brightness we cannot simply subtract a level on each interrupt call since the interrupt call is too fast for the fade to be perceived by the viewer (20 calls would only consume 20,000 microseconds which is too fast to see).

Instead we keep another counter which counts a number of interrupt calls which should occur in between decrementing the actual fade level. Since we know the interrupt is called every 1,000 microseconds it’s pretty straight-forward to work out how many interrupts we should count to get a desired fading rate. For example, if we want a fade from brightness level 19 to 0 to take 0.5 seconds we simply divide the required time (in microseconds) by the interrupt time of 1,000 microseconds and then by the number of levels. Therefore 0.5 seconds (or 500,000 microseconds) = 500,000 / 1,000 = 500 /20 = 25. This is shown in the following code excerpt:

// Globals for PWM
unsigned char pwmCounter = 0;
unsigned char ledActualBrightness = 0;
unsigned char ledTargetBrightness = 0;
 
unsigned char fadeCounter = 0;
 
// Low priority interrupt procedure
void interrupt low_priority lpHandler(void)
{
 // Is this timer0 interrupting?
 if (TMR0IF)
 {
  // Perform the PWM brightness control
  if (ledActualBrightness > pwmCounter)
   LED0 = 1; else LED0 = 0;
 
  pwmCounter++;
  if (pwmCounter > 19) pwmCounter = 0;
 
  // Perform fading control
  if (ledTargetBrightness >= ledActualBrightness)
   ledActualBrightness = ledTargetBrightness;
  else
  {
   fadeCounter++;
   if (fadeCounter == 24)
   {
    ledActualBrightness--;
    fadeCounter = 0;
   } 
  } 
 
  // Get ready for the next interrupt
  TMR0L = 255 - 187; // Reset the timer0 counter
  TMR0IF = 0;  // Clear the timer0 interrupt flag
 }
}

Conclusions

Whilst it is perfectly possible to get PWM controls to work with LEDs using pure guess work, calculating the desired optimum values makes more efficient use of the available processor resources allowing you to both do more with the microcontroller and/or control more LEDs simultaneously from the same chip. The same techniques shown here for LEDs can also be used to control motors, analogue meter displays, incandescent light bulbs, etc.

InfraRed Proximity Detector

2011-03-10T03:26:00.000-08:00

This proximity detector using an infrared detector (Fig. 1) can be used in various equipment like automatic door openers and burglar alarms. The circuit primarily consists of an infrared transmitter and an infrared receiver. The transmitter section consists of a 555 timer IC functioning in astable mode. It is wired as shown in the figure. The output from astable is fed to an infrared LED via resistor R4, which limits its operating current. This circuit provides a frequency output of 38 kHz at 50 per cent duty cycle, which is required for the infrared detector/receiver module. Siemens SFH5110-38 is a much better choice than SFH506-38. Siemens SFH5110-38 is turned on by a continuous frequency of 38 kHz with 50 per cent duty cycle, whereas SFH506 requires a burst frequency of 38k to sense. Hence, SFH5110-38 is used.

The receiver section comprises an infrared receiver module, a 555 monostable multi vibrator, and an LED indicator. Upon reception of infrared signals, 555 timer (mono) turns on and remains on as long as infrared signals are received. When the signals are interrupted, the mono goes off after a few seconds (period=1.1 R7xC6) depending upon the value of R7-C6 combination. Thus if R7=470 kilo-ohms and C6=4.7μF, the mono period will be around 2.5 seconds.
Both the transmitter and the receiver parts can be mounted on a single breadboard or PCB. The infrared receiver must be placed behind the infrared LED to avoid false indication due to infrared leakage. An object moving nearby actually reflects the infrared rays emitted by the infrared LED. The infrared receiver has sensitivity angle (lobe) of 0-60 degrees, hence when the reflected IR ray is sensed, the mono in the receiver part is triggered. The output from the mono may be used in any desired fashion. For example, it can be used to turn on a light when a person comes nearby by energizing a relay. The light would automatically turn off after some time as the person moves away and the mono pulse period is over.
The sensitivity of the detector depends on current-limiting resistor R4 in series with the infrared LED. Range is approximately 40 cm. For 20-ohm value of R4 the object at 25 cm can be sensed, while for 30-ohm value of R4 the sensing range reduces by 22.5 cm.

RESISTOR COLOR CODE

2011-03-08T20:06:00.000-08:00

A resistor is a two-terminal electrical component used in electronic circuits to oppose the flow of an electric current. If an object inserted in a circuit displays a current flow which is proportional to the voltage across it, the ratio of voltage V divided by current I will be constant. This constant ratio is called resistance R=V/I. It can be measured by a device called ohmmeter. In an ideal resistor R does not depend on the current. The Ohm's law states that I=V/R.

Since this is true only for materials that can be characterized by such a resistance, it sounds like a tautology. In reality the Ohm's law should be understood as the statement that there are substances [including solids and liquids], called electrical conductors, that display this kind of behavior, at least within certain range of currents. Physical resistors are characterized by their resistance, maximum power they can dissipate without failure, maximum working voltage, temperature coefficient, noise, and parasitic inductance. The SI unit of electrical resistance is the ohm, symbol Ω. Its reciprocal quantity is conductance measured in siemens. Electronic industry often uses a special coding system of colored stripes to indicate the component's value and tolerance (see resistor color chart). These markings were originally published by Electronic Industries Alliance as EIA-RS-279, and currently are specified by IEC 60062 Ed. 5.0. This graphical calculator works both ways- you can get resistances from color codes or generate the colour bands from ohm values (5%, 10% and 20% tolerance).

Note that only certain "standard" component values specified by Electronic Industries Association (EIA) and IEC publication 60063 may actually be available. See a complete Standard Decade Resistor Values table. Resistors may have different number of color bands depending on the tolerance. The same color scheme is used for capacitors (in picofarads pF) and inductors (in microhenries µH), although they usually have the numeric values actually stamped on them. Also see electrical formulas for the main circuit component connections in series and in parallel.

Parrot Sounding AC door Bell

2011-03-06T23:20:00.000-08:00

Here is a mains-operated doorbell that produces parrot-likesweet voice without requiring any musical IC. The circuit is cheap and easy to construct. The AC mains is fed to the circuit without using any step-down transformer.

The complete circuit is shown in Fig. 1. The main components of the circuit are a resistor-capacitor network, transistor BC337 and audio output transformer X1. The oscillation frequency depends on the combination of resistors R4 and R5 and capacitors C3, C4 and C5. When switch S1 is closed, the audio signal generated due to oscillations is amplified by transistor BC337 and parrot-like sound is reproduced from loudspeaker LS1 connected across the secondary of transformer X1. Here we have used an 8-ohm, 0.5W loudspeaker. The audio output transformer (X1) is normally used in transistor radio. The function of the audio output transformer is to transform the high impedance of the output amplifier to match the much lower impedance of the speaker. This is necessary to get an efficient transfer of the audio signal to the speaker. If a wrong audio transformer is used, the result can be low output and loss of tone quality.

The audio frequency tone across the speaker terminal is about 3 kHz. The dimensions of the audio transformer used in the experimental setup are shown in Fig. 2. The circuit is powered directly from 220V AC mains. The operating DC voltage obtained at the cathode of diode D1 is about 6V. However, if you press switch S1 continuously for a few seconds, the maximum voltage developed at this point may go up to 20 volts, which must be avoided to prolong the life of the circuit. R1 limits surge current in the circuit. The parallel combination of resistor R1 and capacitor C1 limits the circuit current to a safe level for circuit operation. R2 across C1 provides DC path for the current as well as a discharge path when the circuit is switched off. This is to prevent a possible shock to the operator by charged capacitor C1.

STK4050V 200 watt amp

2011-03-04T02:35:00.000-08:00

This 200 watt amp schematic circuit is based on STK4050V high power audio amplifier IC and is designed do deliver up to 200 watts audio power on a single channel .
STK4050V 200 watt amp audio amplifier IC is pin compatibility with other STK amplifiers series .
Because of current mirror circuit application the distortions are reduced to 0.08 % .
STK4050V supports addition of electronic circuits for thermal shutdown and load-short protection circuit as well as pop noise muting which occurs when the power supply switch is turned on and off.
The maximum output power of STK4050V audio amplifier is around 200 watts on 8 ohms load impedance with a 66 volts split power supply .
If you want to make this power amplifier you need to make a separate thermal protection and load short protection circuit because the IC don’t offer these kind of protection and you can destroy the chip and the speaker box .

Musical light chaser circuit

2011-03-03T19:10:00.000-08:00

Circuit Diagram

Description

Here is a simple state of the art musical chaser circuit that can be used in discotheques or even at home if you are a little music crazy .The working of the circuit is straight forward ,the condenser mic pickup the sound and Q1amplifies it.This signal is fed to clock input of IC1 ,CD 4016.The IC is wired in divide by ten mode.The out put of IC1 is given to clock input of IC2, CD4016.The out puts of IC 2 shown in the right side of IC2 in circuit diagram will run run according to the frequency of the input.Result ,we get 10 lights dancing in the according frequency of the sound available.If no sound is there the first light will glow steady.For saving space only arrangement for connecting only one lamp is shown in the diagram.Make 9 lamp arrangements like the one shown in figure and connect each if them to the each outputs of IC2 with the other ends connected to the circuit as that of one shown in circuit.

The power supply for the circuit is directly derived from the mains itself using D2 , R9,C4,C3 and D3, which adds an extra bonus of avoiding the bulky transformer to make the circuit compact.

Notes

If the output doesn't respond to the music and only the first light remains glowing, adjust the level of input signal to IC1 by adjusting R1 since the cause of problem is the low voltage level of input to IC1.Problem is solved.
Some parts of the circuit are live with potential shock hazard.So be careful.

Sound Level Meter

2011-03-03T19:07:00.000-08:00

Circuit Diagram

Description

This is a one chip sound level meter that can be use for displaying sound level of an amplifier or simply the sound level from a microphone.The heart of the circuit is IC LM 3915 Audio level IC.Even though it is a stand alone IC , a peak detector based on Transistor BC 558 and diode 1N4001 is also included for better performance.

Tips

Supply voltage can be from 3V to 20V.The input is set for audio line voltage (1V peak to peak) and has a max input voltage of 1.3V. To make the circuit use a moving dot display instead of bar graph display,Pin 9 can be should be disconnected from +V.

Parts List.
C1 2.2uF 25V Electrolytic Capacitor
C2, C3 0.1uF Ceramic Disc Capacitor
R1, R3 1K 1/4W Resistor
R2 10K 1/4W Resistor
R4 100K 1/4W Resistor
R5 1M 1/4W Resistor
D1 1N4001 Silicon Diode
Q1 BC 558 PNP Transistor
LED1-LED10 Standard LED or LED Array
U1 LM3915 Audio Level IC
MISC Board, Wire, Socket For U1

Ultra Bright LED Lamp

2011-03-02T19:01:00.000-08:00

This ultra-bright white LED lamp works on 230V AC with minimal power consumption. It can be used to illuminate VU meters, SWR meters, etc. Ultra-bright LEDs available in the market cost Rs 8 to 15. These LEDs emit a 1000-6000mCd bright white light like welding arc and work on 3 volts, 10 mA. Their maximum voltage is 3.6 volts and the current is 25 mA. Anti-static precautions should be taken when handling the LEDs.

The LEDs in water-clear plastic package emit spotlight, while diffused type LEDs have a wide-angle radiation pattern. This circuit (Fig. 1) employs capacitive reactance for limiting the current flow through the LEDs on application of mains voltage to the circuit. If we use only a series resistor for limiting the current with mains operation, the limiting resistor itself will dissipate around 2 to 3 watts of power, whereas no power is dissipated in a capacitor. The value of capacitor is calculated by using the following relationships:

XC = 1/(2pfC) ohms —————(a)
XC = VRMS /I ohms ———— (b)

where XC is capacitive reactance in ohms, C is capacitance in farads, I is the current through the LED in amperes, f is the mains frequency in Hz, and Vrms is the input mains voltage. The 100-ohm, 2W series resistor avoids heavy ‘inrush’ current during transients. MOV at the input prevents surges or spikes, protecting the circuit. The 390-kilo-ohm, ½-watt resistor acts as a bleeder to provide discharge path for capacitor Cx when mains supply is disconnected.

The zener diode at the output section prevents excess reverse voltage levels appearing across the LEDs during negative half cycles. During positive half cycle, the voltage across LEDs is limited to zener voltage. Use AC capacitors for Cx. Filter capacitor C1 across the output provides flicker-free light. The circuit can be enclosed in a CFL round case, and thus it can be connected directly to AC bulb holder socket.

A series combination of 16 LEDs (Fig. 2) gives a luminance (lux) equivalent of a 12W bulb. But if you have two series combinations of 23 LEDs in parallel (total 46 LEDs as shown in Fig. 3), it gives light equal to a 35W bulb. 15 LEDs are suitable for a table-lamp light. Diode D1 (1N4007) and capacitor C1 act as rectifying and smoothing elements to provide DC voltage to the row of LEDs. For a 16-LED row, use Cx of 0.22 µF, 630V; C1 of 22 µF, 100V; and zener of 48V, 1W. Similarly, for 23+23 LED combination use Cx of 0.47 mF, 630V; C1 of 33 µF, 150V; and zener of 69V, 1W.

Fading LED by LM358

2011-02-28T02:33:00.000-08:00

This circuit uses op-amps to obtain a triangle wave. The triangle wave causes the Led to slowly get brighter and then slowly get dimmer until it isn’t producing any light. It then gets slowly brighter again. With the components shown each cycle takes about 4 seconds. The capacitor and the 4.7M resistor are the timing components. The circuit works best when a high brightness Led is used.

Classic LED Flasher Circuit

2011-02-25T04:19:00.000-08:00

This LED flasher circuit is a classic two transistor flip flop. This flasher circuit is very popular and it’s usually the first circuit to build when starting electronic circuit building hobby. Here is the schematic diagram of the famous LED flasher circuit:

How LED Flasher Circuit Works

The circuit consist of two transistors, two capacitors, four resistors, and two LEDs. When the power supply is first connected to this LED flasher circuit, both transistor is racing to be triggered first by the base current through 100k resistor. Actually when one transistor is triggered first than the other, the first activated transistor will behave like a closed switch, so the LED will turn ON and the base of the other transistor will be grounded through the capacitor. This grounding keep the first transistor to be activated and the second one to stay off untill the capacitor is charged above the bias voltage needed to activate the second transistor. After reaching this voltage, the second transistor will be switched on and now the second transistor will turn ON the LED on its collector, turning off the first transistor by grounding its base through the second capacitor. This alternating process will be repeated forever until the power supply is turned off. The flashing rate will depend on the resistors (100k) and the capacitors values. You can change the values of the capacitors to change the flashing frequency. Use a higher capacitance value for lower flashing rate, and vice verse.

Emergency Light & Alarm

2010-12-14T19:08:00.000-08:00

Device purpose:

This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen.
When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to extend lamp or alarm operation even when power is restored.

Circuit operation:

Mains voltage is reduced to about 12V DC at C2's terminals, by means of the reactance of C1 and the diode bridge (D1-D4). Thus avoids the use of a mains transformer.
Trickle-charging current for the battery B1 is provided by the series resistor R3, D5 and the green LED D6 that also monitors the presence of mains supply and correct battery charging.
Q2 & Q3 form a self-latching pair that start operating when a power outage occurs. In this case, Q1 biasing becomes positive, so this transistor turns on the self latching pair.
If SW3 is set as shown in the circuit diagram, the lamp illuminates via SW2, which is normally closed; if set the other way, a square wave audio frequency generator formed by Q4, Q5 and related components is activated, driving the loudspeaker.
If SW1 is left open, when mains supply is restored the lamp or the alarm continue to operate. They can be disabled by opening the main on-off switch SW2.
If SW1 is closed, restoration of the mains supply terminates lamp or alarm operation, by applying a positive bias to the Base of Q2.

Notes:

Close SW2 after the circuit is plugged.
Warning! The circuit is connected to 220Vac mains, then some parts in the circuit board are subjected to lethal potential!. Avoid touching the circuit when plugged and enclose it in a plastic box.

Parts:

R1____________220K   1/4W Resistor
R2____________470R   1/2W Resistor
R3____________390R   1/4W Resistor
R4______________1K5  1/4W Resistor
R5______________1R   1/4W Resistor
R6_____________10K   1/4W Resistor
R7____________330K   1/4W Resistor
R8____________470R   1/4W Resistor
R9____________100R   1/4W Resistor

C1____________330nF  400V Polyester Capacitor
C2_____________10µF   63V Electrolytic Capacitor
C3____________100nF   63V Polyester Capacitor
C4_____________10nF   63V Polyester Capacitor

D1-D5________1N4007 1000V 1A Diodes
D6______________LED  Green (any shape)
D7___________1N4148   75V 150mA Diode

Q1,Q3,Q4______BC547   45V 100mA NPN Transistors
Q2,Q5_________BC327   45V 800mA PNP Transistors

SW1,SW2________SPST Switches
SW3____________SPDT Switch

LP1____________2.2V or 2.5V 250-300mA Torch Lamp

SPKR___________8 Ohm Loudspeaker

B1_____________2.5V Battery (two AA NI-CD rechargeable cells wired in series)

PL1____________Male Mains plug

Enjoy.......

LED STEREO SOUND LEVEL INDICATOR

2010-12-13T23:13:00.000-08:00

Many circuits can be designed as level indicators by using a comparator IC or transistors but these are costly and complex and also time consuming. This circuit removes all the complexity by using a single TA7666p IC. LEDs are used as a power indicator. Different colour LEDs can be used for both the channels. One can also use an LED bargraph display. INPUT signals should be given from preamplifiers. Otherwise, LEDs will not glow at low volumes.

PARTS LIST
R1-R10	1kΩ
R11	15kΩ
R12	15kΩ
C1	0.1µF
C2	0.1µF
C3	1µF 16V
C4	1µF 16V
D1-D10	10 LEDs
IC1	TA7666P

If you have mono systems, signals should be given into both the channels. The input is given through two 4.7 µF capacitors and two 18k resistors to pins 1 and 16 respectively.

Suitable for stereo LED driver
Wide Supply Voltage Range : V_CC= 6V to 12V
Low Quiscent Current : I_CCQ = 4ma (typ.) at V_cc = 9V
Variable Voltage Gain Because of Inverting Amplifier
Easy Arrangement for Dual 10 LED’s Driver by Series Connection of TA77666P and TA7667P

Audio VU Meter

2010-12-13T22:56:00.000-08:00

This circuit uses two quad op-amps to form an eight LED audio level meter. The op-amp used in this particular circuit is the LM324.

The 1K resistors in the circuit are essential so that the LED's turn on at different audio levels. There is no reason why you can't change these resistors, although anything above 5K may cause some of the LED's to never switch on. This circuit is easily expandable with more op-amps, and is not limited to use with the LM324. Pretty much any op-amp will work as long as you look up the pinouts and make sure everything is properly connected.

The 33K resistor on the schematic is to keep the signal input to the circuit at a low level. It is unlikely you will find a 33K resistor, so the closest you can get should do. The value of this resistor may need to be changed, so it is best you breadboard this circuit before actually constructing it on PCB. The circuit in it's current form will accept line level inputs from sources such as the aux out on a Hi-Fi, all though could be easily modified to accept speaker inputs.

The audio + is connected to the main positive rail, while the audio - is used for signal input. The 50k pot can be used to vary the sensitivity of the circuit.

Battery Charger for 12V SLA

2010-12-09T23:24:00.000-08:00

Battery Charger for 12v SLA(Sealed Lead-Acid) Batteries

HOW THE CIRCUIT WORKS

The circuit does not turn on until a battery is connected across the terminals as shown in the diagram. (A push switch has been provided to start the circuit when a totally flat battery is fitted.)
This action turns on the PNP transistor in the "Turn ON" block. The resistance between the collector-emitter terminals decreases and the indicator LED comes on.
The path to the bottom rail of the circuit goes through a signal diode, the gate-cathode junction of the SCR and through two 1R8 resistors in parallel. This is why the LED illuminates.

MUST USE AC PLUG PACK
Before we go any further, the circuit works on an AC plug pack. It must be an AC supply as we do not want any electrolytics to be present on the power rail as this will allow a very high charge-current to flow and possibly damage the SCR.
A DC supply will not allow the SCR to turn off, as it turns off when the current through it falls to zero.

THE CIRCUIT IS A HALF-WAVE RECTIFIER!
The circuit is actually a half-wave rectifier. It only charges the battery on every half cycle. The plug pack doesn't like this as it leaves residual flux in the core of the transformer and causes it to overheat. But that's the only drawback with the circuit.
The SCR turns on during each half cycle and current flows into the battery.
A voltage is developed across the two 1R8 resistors (in parallel) and this voltage is fed into the 47u electrolytic. It charges and turns on the BC547 transistor.
The transistor robs the SCR of gate voltage and the SCR turns off. The energy in the 47u feeds into the transistor but after a short time it cannot keep the transistor turned on.
The transistor turns off and the SCR switches on and delivers another pulse of current to the battery.
As the battery charges, its voltage increases and this is monitored by the "Voltage Monitor" block.
The circuit is very complex and one way to look at the operation is to consider the top rail as a fixed rail and as the battery voltage increases, the rail connected to the negative terminal of the battery is pushed down.
This lets you see how the "Turn On" transistor is activated and how the "Voltage Monitor" components create voltage drops across each of them.
The "Voltage Monitor" components consist of a transistor and zener diode as well as an 8k2 resistor, the 1k pot, a 1k5 resistor, a 150R resistor and a signal diode.
The signal diode is actually part of the flasher circuit and we discuss its operation later.
As the voltage across the battery increases to 13.75 volts, each resistor in the "voltage detecting network" will have a voltage drop across it that corresponds to the resistance of the resistor. The diode will have a constant 0.7v across it.
The voltage on the wiper of the pot will be about 3.25v and the voltage across the zener will be 10v. This leaves 0.6v between the base and emitter of the Voltage Monitor transistor.
This voltage is sufficient to turn the transistor ON.
When the Voltage Monitor transistor turns ON, it robs the "Turn On" transistor of base-emitter voltage and the circuit turns off.
The SCR has only two states: ON and OFF.
During the half-cycle when it is turned on, the battery gets a high pulse of current and the current is only limited by the capability of the plug pack.
There are no electrolytics to allow very high pulses of current to be delivered and this is fortunate as the SCR is only a 0.8 amp device, but will endure surges of 10amp for half a cycle.
Whenever the SCR is triggered into conduction during the half cycle of its operation, it remains in conduction until the voltage delivered by the plug pack falls to zero. This is when the SCR turns off.
When the plug pack delivers a negative voltage to the top rail and a positive voltage to the lowest rail, the SCR is not triggered into conduction and none of the components in the circuit deliver current to the battery. The SCR delivers current for a few half-cycles and then it is turned off for a few cycles. This is how the average current delivered to the battery is controlled.
The circuit is designed to deliver about 300 - 400 mA average charge-current. The actual value is determined by the 1R8 resistors.
When the battery is fully charged, the indicator LED begins to flash.
The flashing is produced by the 2k2 resistor and 47u (connected to the voltage monitor section).
When the battery is charging, the 47u is charged via the diode connected to the BC557 transistor and through the 150R and signal diode to the negative of the battery.
When the battery is fully charged, the Voltage Monitor section turns ON and turns off the "Turn ON" section.
This removes the voltage on the positive side of the 47u and the positive side is brought to the negative rail via the 2k2 resistor. This brings down the negative side of the 47u and the 150R resistor is allowed to drop below the negative rail due to the presence of the diode, as the diode becomes reverse-biased.
This holds the circuit in the "off" condition, as the voltage monitor section sees an extra voltage across it and thinks the battery it is "over-charged."

The 47u discharges and the circuit turns ON to pump a small burst of current into the battery to keep it charged. This is called "Trickle Mode" or "Pulse Mode."

DEAD BATTERIES
The circuit will not turn on if the voltage of the battery you are charging is less than 4 volts.
If you have a good battery that has been totally discharged, you can manually start the charging process by connecting the battery and pressing the button. This will raise the voltage
on each cell and the circuit will take over in the normal way once the voltage rises more than 4 volts.

SCR: MCR100
type - 6	400v
current	0.8A
Max current for half cycle	10A

PARTS LIST
12v SLA Battery Charger

2 - 1R8 0.5watt resistors
1 - 150R 0.25 watt resistor
1 - 180R
1 - 560R
1 - 1k5
3 - 2k2
1 - 3k3
1 - 4k7
1 - 8k2
1 - 1k mini trim pot

1 - 1n ceramic
2 - 47u 25v electrolytics

1 - 5mm red LED

4 - 1N4148 signal diodes
1 - 10v 0.25watt zener
1 - BC 547 transistor
2 - BC557 transistors
1 - MCR100-6 SCR
1 - 1m red lead
1 - 1m black lead
2 - alligator clips
1 - 2m very fine solder

1 - SLA Battery Charger PCB

Also required:
1 - 12v AC transformer (500mA AC)
1 - power lead
1 - case

Knight Rider Lights Project

2010-11-29T22:57:00.000-08:00

This is a simple knight Rider light system that can be built using well known popular integrated circuits.

Circuit diagram for standard LED output.

This set up is ideal for running off a car battery.

You can use 12V bulbs for the output, simply substitute the IC for the LEDs, the bulbs are then connected to the IC's outputs.

Components List

PARTS LIST

ICs	DIODES	BULBS	RESISTORS	CAPACITORS
1*NE555	8* 1N4148		6* 1K	1* 10uF
1* 4017B			1* 3.3K	1* 0.01uF
			1* 8.2K	1* 6.8nF
	6* LED		1* 10K
Bulb Version			1* 100K
1* ULN2001N		6* 12V/2.2W
Plus 6* suitable Bulb Holders.

Led Clock

2010-11-28T19:32:00.000-08:00

12Hr Led clock using 16F628.

Using only 2 capacitors, 3 resistors, 4 seven-segment Display, 1 xtal, 2 switches n.o. and 1 Microcontroller PIC, you can build this Digital Led Clock. you can use common anode or common cathode display, just select the display type. Here is the pinout information:

Pin 3 defines the display type. If you will use common cathode display, connect to negative. For common anode, connect to positive. Here is a example circuit:

The minutes displays are upside down.
For the capacitors, I used 30pf. You have to read the xtal manufacturer specifications to know the capacitor value recommended. Short connections on xtal is a must to keep accuracy.

Use your PIC programmer to program your PIC16F628 device.

Thank you Jose.

Bar Graph LED Project

2010-11-23T23:28:00.000-08:00

This bar graph LED battery level indicator project is based on LM3914 monolithic ic from National Semiconductor that senses the voltage levels of the battary and drives the 10 light emitting diodes based on the voltage level that is detected.

It provides a linear analog display output and has a pin that can be configured to display the output in moving dot or bar graph. The current driving the LEDs is regulated and programmable hence limiting resistors are not required.

The schematic shows how the various components are connected. Switch S1 is used to change the display type from moving dot to bar graph type. When S1 is ON, the display type is bargraph but when it is OFF the display changes to moving dot type. VR1 is used to set the lower limit of the display. By using a variable DC power supply, set the VBAT to 10.5V. Adjust VR1 until the LED L1 turns ON. Next, set the VBAT to 15V, adjust VR2 until all the LEDs turn ON (When S1 is ON). The specifications of LM3914 can be obtained from National Semiconductor Website.

Parts List