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EEE, ECE & IE Project Updates

EEE, ECE & IE Project Updates

Link to Electronics Hub

Low Power Audio Amplifier using 555 Timer

Posted: 11 Jun 2014 03:26 AM PDT

Conventional methods of audio amplification use high power circuits to drive a loudspeaker for areas like an auditorium or any other hall. However for applications involving use of small loudspeakers for low range requirements, we can meet the requirements by constructing a low power amplifier with a low output current such as 200 mA.

In this article we are describing the principle, design and operation of a low power audio amplifier using 555 Timer. The 555 Timer generates a carrier signal which is modulated by the amplified audio signal to produce a modulated signal. This signal is used to drive a small loudspeaker.

Low Power Audio Amplifier Circuit Principle:

Here this circuit is based on the principle of audio amplification using operational amplifier and pulse width modulation using 555 Timer. The audio signal is amplified using low noise high input operational amplifier TL071 and is fed to the control pin of the 555 Timer. 555 Timer is used as an astable multivibrator producing an oscillating signal. This signal is modulated by the audio signal such that the width of the output pulse varies with respect to the voltage at the control pin (the audio signal), causing pulse width modulation.

555 Timer as an Amplifier Circuit Diagram:

Circuit Diagram of 555 Timer as an Amplifier

Circuit Diagram of a Low Power Audio Amplifier using 555 Timer – Electronics Hub

Circuit Design of Low Power Audio Amplifier:

Here the circuit designing is a simple process involving just two steps – designing the preamplifier section and designing the astable multivibrator section.

Here we are using a low noise JFET input operational amplifier TL071 with low input bias current and high slew rate of about 13V/µs. A voltage divider network is designed using two resistors each of 47K, so that a voltage of 6V is applied to the non inverting terminal of the OPAMP. Assuming our required gain to be around 22(V/V) or 27.2dB and the value of one of the feedback resistors to be around 1K, we calculate the value of another resistor to be around 22K. Since output impedance is low for this amplifier, we use a resistor of about 1K at the output to connect it to the control pin of the 555 Timer.

Next step in the design process involves designing the 555 timer astable circuit.  In normal circuit connection for 555 Timer as astable multivibrator, we use two resistors for both charging and discharging of the capacitor. However to provide faster discharge rate, we use here a diode 1N4007 instead of the resistor. Here our required output frequency is around 145 KHz and assuming the value of capacitor to be around 10nF, we can calculate the value of threshold resistor to be around 1K (Forward resistance of 1N4007 is around 1Ohms).

Related Post – 100w Subwoofer Amplifier Circuit

Low Power Audio Amplifier using 555 Timer Circuit Simulation:

Once the circuit is designed, the next step involves circuit simulation. Here we follow a series of steps to simulate the circuit using Multisim software.

  1. The microphone simulation model is selected from the LabView instruments under Simulate menu.
  2. Required parameters are set accordingly (The time of recording and sampling rate).
  3. The designed circuit is build using the software and the microphone is connected as input to the circuit.
  4. A loudspeaker model is selected from the LabView instruments under Simulate menu and connected as output to the circuit
  5. The interactive simulation setting is accomplished by setting the end time equal to or more than the time of recording.
  6. As long as the circuit simulation takes place, the 'Play' button of the loudspeaker is grayed out and once the simulation ends, the button is enabled.

How 555 Timer as an Amplifier Circuit Works?

The circuit operation is divided into two segments – the pre amplifying (electric signal amplification) operation and the pulse width modulation operation. The amplifying operation is performed by the low noise operational amplifier TL071. The input audio signal is sensed using the microphone and converted to a low voltage electric signal. This low voltage AC signal is fed to the non inverting terminal of the OPAMP through an electrolyte capacitor of 1uF, which blocks the DC current of the audio signal. This signal is amplified using the operational amplifier with a gain depending upon the values of feedback resistors. Here the OPAMP works in linear mode so as to make the voltage at non inverting terminal equal to the output voltage using the feedback network. This amplified signal is then fed to the control pin of the 555 Timer through the capacitor (to remove the DC component) and the resistor. Here the 555 Timer works in the astable mode with the frequency of output signal determined by the combination of resistors R1 and C1. However since here we are applying the control voltage, the width of the output pulse varies depending upon the control voltage. The carrier output signal produced by the 555 Timer is modulated by the audio voltage and the resultant modulated signal is used to the drive the loudspeaker. Here the loudspeaker does not responds to the high frequency signal, but rather to the DC value of the modulated signal and thus the audio signal appears amplified.

555 Timer as an Amplifier Circuit Applications:

  1. This application can be used to develop low power music systems used in vehicles.
  2. It can be used in classrooms with limited areas.

Limitations of Audio Amplifier Circuit:

  1. This circuit is suitable only for low power loudspeakers.
  2. 555 Timer doesn't produce 50% duty cycle signal.
  3. This circuit is theoretical and may require changes in hardware implementation.

The post Low Power Audio Amplifier using 555 Timer appeared first on Electronics Hub.

Street Lights that Glow on Detecting Vehicle Movement

Posted: 10 Jun 2014 11:26 PM PDT

Generally, street lights are switched on for whole night and during the day, they are switched off. But during the night time, street lights are not necessary if there is no traffic. Saving of this energy is very important factor these days as energy resources are getting reduced day by day. Alternatives for natural resources are very less and our next generations may face lot of problems because of lack of these natural resources. We have already seen the circuit diagram and working of Auto Intensity Control of Street Lights circuit in the earlier post. This article describes about the circuit that switches the street lights on detecting vehicle movement and remains off after fixed time.

Principle Behind this Circuit:

The proposed system consists of Atmega8 microcontroller, LDR, PIR sensor and RTC. This system controls the street lights using light dependent resistor and PIR sensor.

Street lights are switched on depending on the intensity of the Sun light on LDR. If the intensity of Sunlight on light dependent resistor is low, its resistance value is high. This value increases and becomes high when it is completely in dark. This resistance value decides when the street lights are required to switch ON.

As the resistance value is maximum in the midnights, real time clock comes into the play. The controller checks peak time during which there is no traffic and switch OFF the lights. When there is any vehicle on the road, it is detected by the PIR sensor.

Whenever PIR sensor is detected it just indicates the microcontroller to switch on the street lights. Then lights are switched on for 2 to 3minutes and switched off automatically.

Another way to this approach is, one can maintain minimum intensity without completely switching off the lights by using PWM and switch them on to maximum intensity whenever it detects the vehicle. But in this article the circuit is designed in such a way that lights are completely switched OFF and will be switched ON only when there is any vehicle. 

Circuit Diagram of Street Lights that Glow on Detecting Vehicle Movement Project:

Street Lights That Glow on Vehicle Movement Circuit Diagram

Circuit Diagram of Street Lights That Glow on Vehicle Movement – Electronics Hub

 

Circuit Components:

  • ATmega8 microcontroller
  • DS1307 IC
  • PIR sensor
  • LDR
  • LCD
  • LED array

Street Lights that Glow on Detecting Vehicle Movement Circuit Design:

The proposed circuit consists of ATmega8 microcontroller, PIR sensor, light dependent resistor and real time clock, Liquid Crystal Display.

Passive Infrared sensor, also called as PIR sensor is connected to the PD0 pin of the microcontroller. PIR sensor senses the motion of the objects.

The PIR sensor internally will have an IR detector. Every object in the world radiates some IR rays. These are invisible to the human eye but electronic components can detect them. Different objects will emit IR rays of different wavelength. These rays were detected by the PIR sensor. PIR is initially high and is set to low automatically after sometime. Whenever it detects the motion of any object, it becomes low.

LDR is connected to the ADC pin – ADC0 of the microcontroller as LDR will produce analog value which is converted to digital by the ADC.

Light dependent resistors will have low resistance in light and high resistance in dark. The resistance of Light dependent resistor in dark is in range of ohms and in dark its resistance is in the range of mega ohms. When the light falls on LDR it resistance is reduced to a great extent.

Real time clock IC used is DS1307, which is I2C compatible. Real time clock has 8 pins.1 and 2 pins are connected to the crystal oscillator.3rd pin is connected to a battery.6th pin of RTC is connected to PC5 pin of microcontroller.5th pin is connected to PC4 pin of microcontroller.

I2C is inter integrated circuit. This is two wire interface protocol in which only two signals were used to transmit the data between two devices.

LCD is used for displaying time. LCD interfacing in 4bit mode is shown in the circuit diagram. Time from RTC is read and displayed on the LCD.

How to Operate this Circuit?

  1. Initially power the circuit.
  2. LCD displays the time read from RTC.
  3. Place the LDR in darkness. Now street light is switched ON.
  4. Now micro controller continuously checks the time. Street Light is switched on for fixed timings written in the code.
  5. After this time, they are switched of automatically.
  6. Place your hand in front of PIR sensor, this switches the street lights again, indicating that on the detection of any object street light is ON.
  7. After 2-3 seconds delay, lights are again switched of automatically.

Also Read the Related Post – Automatic Street Light Controller using Relays and LDR

Street Lights that Glow on Detecting Vehicle Movement Circuit Applications:

  1. This circuit can be used in real time street lights and highways also.
  2. This can be used for lights in parking areas of industries, hotels, restaurants, etc. 

Main Advantages of this Circuit:

  • This circuit uses LED Bulbs, so it is very low cost and it has more life span.
  • Maximum energy can be saved.

The post Street Lights that Glow on Detecting Vehicle Movement appeared first on Electronics Hub.

Auto Intensity Control of Street Lights

Posted: 10 Jun 2014 10:14 PM PDT

Street lights are controlled manually in olden days. These days automation of street lights has emerged. But one can observe that there is no need of high intensity in peak hours i.e. when there is no traffic and even in early mornings. By reducing the intensity in these times, energy can be saved to some extent. We have already published a post about Automatic Street Light Controller circuit which was designed using Relays and LDRs. This article explains the circuit that automatically controls the intensity of street lights which is designed using microcontroller and LEDs.

Auto Intensity Control of Street Lights Circuit principle:

The circuit consists of ATmega8 controller, Real time clock and LDR. Depending on the time and LDR value, micro controller automatically adjusts the intensity of the street lights using pulse width modulation. In this article, Pulse width modulation signal is generated in ATmega8 micro controller using timer/counter-2 at OCR2 i.e. PB3 pin.

Real time clock IC used is DS1307. It is compatible to I2C protocol. RTC acts as a slave. Time is read from RTC IC and micro controller automatically adjusts the intensity of light by generating PWM signal.

Light Dependent Resistor (LDR) is used in this project to check the intensity of light. Depending on the intensity, lights can be switched ON or OFF. Both light dependent resistor and real time clock are required for this project. Because, using Light dependent resistor alone may lead to wastage of energy. Using RTC alone may cause the lights to be switched on even when there is light.

Auto Intensity Control of Street Lights Circuit diagram:

Auto Intensity Control of Street Lights Circuit Diagram

Circuit Diagram of Auto Intensity Control of Street Lights – Electronics Hub

Circuit Components:

  • ATmega8 micro controller
  • DS1307 IC
  • Light Dependent Resistor
  • LED array.
  • LCD display

Related Post – Street Lights that Glow on Detecting Vehicle Movement

Auto Intensity Control of Street Lights Circuit design:

The auto intensity control of street lights circuit is simple but it requires more coding part. This circuit consists of Atmega8 controller, DS1307, LDR, Relay and LEDs. The light dependent resistor is connected to ADC1 (PC1) pin of the micro controller. The analog light value is converted to digital value using ADC.

Real time clock has 8 pins out of which SCL and SDA are connected toPC5 and PC4 pins respectively. SCL is serial clock while SDA is serial data. As said before, RTC is I2C compatible, where I2C means inter integrated circuit. One bit of data is transmitted on data bus for each clock cycle. I2C protocol allows one to connect 128 devices. Data can be transferred between devices, using only two bi-directional buses. Each device can act as a slave or master. The slave devices will have one address and these devices can be accessed using this address.

LCD is the display used for displaying time which is read from RTC IC. Interfacing of LCD in 4bit mode is shown in circuit diagram. D4-D7 pins of LCD are connected to PD0-PD3 pins of microcontroller. RS pin of LCD is connected to PD4 pin of micro controller. RW and Enable pins are connected to PD5 and PD6 pins of controller.

LED array is number of high power LEDs connected in series. It is connected to PWM pin of the microcontroller.

I2C Protocol:

I2c is a communication protocol invented by Philips Company. This is well suited for communication between integrated circuits and pheripherals. This uses two lines to transfer data.

  • Serial Data – SDA
  • Serial Clock – SCL.
  1. This can connect up to 128 devices using two wires. Each device connected will have an address. The device which initiates the data transfer is called Master.
  2. Every device will have 7 bit address.
  3.  Master initially sends the START bit on the data line.
  4. Then it sends the address of the device with which wants to communicate and the mode of operation i.e. read or write.
  5. The slave devices listen to the incoming data and checks if its address matches to the received data. The device whose address matches send an acknowledgement signal.
  6. Then master starts transmitting or receiving the data from the slave.
  7. After completion of the transmission, Master sends a STOP bit.
  8. Data on SDA can be changed only if SCL pin is low.

How Auto Intensity Control of Street Lights Circuit Works?

  1. Initially power the circuit.
  2. Time is displayed on the LCD display.
  3. Place the LDR in darkness as the street lights switches on only when there is no light on LDR.
  4. Now check the time if the time is between 9 pm to 2 am street light glows with full intensity.
  5. Change the time by writing time to RTC and dump the code again.
  6. Now switch on the circuit check the intensity. From 2pm intensity of the lights slowly starts decreasing and finally in early morning it glows with least intensity. When the light is sensed by the LDR lights are switched off automatically.

Code is written in such a way that up to 2 am lights will glow with full intensity. From then it slowly starts decreasing and finally it drops to zero in the morning.

Auto Intensity Control of Street Lights Circuit Advantages:

  • Power wastage can be reduced.
  • Using LED array reduces the cost.
  • Using of RTC and LDR produces accurate results.

Limitations of this Circuit:

  • Even though energy is saved if there are any vehicles after fixed time, intensity of the light is low.
  • Maximum energy cannot be saved.

The post Auto Intensity Control of Street Lights appeared first on Electronics Hub.