555 Timer Oscillator

A voltage-controlled oscillator (VCO) using the timer 555 is shown in figure.

555-timer-voltage-controlled-oscillator

The circuit is sometimes called a voltage-to-frequency converter because the output frequency can be changed by changing the input voltage.

As discussed in previous blog posts, pin 5 terminal is voltage control terminal and its function is  to control the threshold and trigger levels. Normally, the control voltage is ++2/3V_CC because of the internal voltage divider. However, an external voltage can be applied to this terminal directly or through a pot, as illustrated in figure, and by adjusting the pot, control voltage can be varied. Voltage across the timing capacitor is depicted in figure, which varies between +V_control and ½ V_control. If control voltage is increased, the capacitor takes a longer to charge and discharge; the frequency, therefore, decreases. Thus the fre­quency can be changed by changing the control volt­age. Incidentally, the control voltage may be made available through a pot, or it may be output of a transistor circuit, op-amp, or some other device.

Mobile incoming call indicator

Description

This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated.

When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

Circuit diagram with Parts list

Notes. 

• The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia plastic former.Or you can purchase a 10 uH coil from shop if available.
• The circuit can be powered from a 6V battery.
• Assemble the circuit on a good quality PCB.
• C1 & C3 are to be polyester  capacitors.
• The electrolytic capacitor C2 must be rated 10V.

9 V regulator using 7809

Description.

Here is the circuit diagram of 9 V regulator using popular 7809 IC.The 7809 is a 9 V voltage regulator IC with features such as internal current limit,safe area protection,thermal protection etc.A 16 V transformer brings down the 230V mains  , 1A bridge rectifier rectifies it and capacitor C1 filters it and 7809 regulates it to produce a steady9V DC  output.


Circuit diagram with Parts list. 

Notes. 

• If a current of 300 mA or above is required ,fit a proper heat sink to the IC 7809.
• If 1A bridge is not available,make one using four 1N 4007 diodes.

Street light circuit

Description.

The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises.In fact you can this circuit for implementing any type of automatic night light.

The circuit uses an LDR to sense the light .When there is light the resistance of LDR will be low.So the voltage drop across POT R2 will be high.This keeps the transistor Q1 ON.The collector of Q1(BC107) is coupled to base of Q2(SL100).So Q2 will be OFF and so do the relay.The bulb will remain OFF.

When night falls the resistance of LDR increases to make the voltage across the POT R2 to decrease below 0.6V.This makes transistor Q1 OFF which in turn makes Q2 ON. The relay will be energized and the bulb will glow.

Circuit diagram with Parts list.

Notes.

• POT R2 can be used to adjust the sensitivity of the circuit.
• You can use bulb of any wattage ,provided that relay should have the sufficient rating.
• The circuit can be powered from a regulated 9V DC power supply.
• Click Here! to get the power supply circuit for this project.
• The relay K1 can be a 9V SPDT relay.

555 Timer as an Astable Multivibrator

An astable multivibrator, often called a free-running multivibrator, is a rectan­gular-wave generating cir­cuit. Unlike the monostable multivibrator, this circuit does not require any ex­ternal trigger to change the state of the output, hence the name free-running. Before going to make the circuit, make sure your 555 IC is working. For that go through the article: How to test a 555 IC for working An astable multivibrator can be produced by adding resistors and a capacitor to the basic timer IC, as illustrated in figure. The timing during which the output is either high or low is determined by the externally connected two resistors and a capacitor. The details of the astable multivibrator circuit are given below.

Take a look @ 555 Ic Pin configuration and 555 block diagram before reading further.

Pin 1 is grounded; pins 4 and 8 are shorted and then tied to supply +Vcc, output (V_OUT is taken form pin 3; pin 2 and 6 are shorted and the connected to ground through capacitor C, pin 7 is connected to supply + V_CC through a resistor R_A; and between pin 6 and 7 a resistor R_B is connected. At pin 5 either a bypass capacitor of 0.01  F is connected or modulation input is applied.

555 Tester circuit

Description.

NE555 is an IC which is widely used in timers and control circuits. A circuit for independent testing this IC is given here.

Here the NE555 is wired as an astable multivibrator. When the push button switch S1 is pressed the LEDs D1 & D2 will flash alternatively. That is when output is high D2 will glow & when output is low D3 will glow. The rate of flashing will depend on components R1,R2 & C1.

When push button S1 is pressed,C1 will start charging through R1&R2.When the voltage across C1 rises above 2 of 3 is the supply voltage the internal Flip Flop toggles . The pin 7 becomes low & C1 starts discharging. When the voltage across C1 goes below 1of 3 of supply voltage the internal Flip Flop resets & pin7 goes high. The C1 again starts charging.All this will take place if the IC is healthy.

According to the frequency of this charging & discharging D1&D2 will flash. From these observations we can conclude that IC NE555 is faulty or not .

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
• Power the circuit from a 9V radio battery.
• If D1 and D2 flashes on the pressing of S1,we can assume that the IC is working.

555 Timer as Monostable Multivibrator

A monostable multivibrator (MMV) often called a one-shot multivibrator, is a pulse generator circuit in which the duration of the pulse is determined by the R-C network,connected externally to the 555 timer. In such a vibrator, one state of output is stable while the other is quasi-stable (unstable). For auto-triggering of output from quasi-stable state to stable state energy is stored by an externally connected capaci­tor C to a reference level. The time taken in storage determines the pulse width. The transition of output from stable state to quasi-stable state is accom­plished by external triggering. The schematic of a 555 timer in monostable mode of operation is shown in figure.

555 Timer – A Complete Basic Guide

A complete basic tutorial of 555 Timer IC.

This article covers every basic aspect of 555 Timer IC. You may already know that SE/NE 555 is a Timer IC introduced by Signetics corporation in 1970′s. In this article we cover the following information about 555 Timer IC.

1. Introduction to 555 Timer IC

2. 555 Timer IC Pin Configuration

3. Basics of 555 Timer

4. Block Diagram

5. Working Principle

1. Introduction

One of the most versatile linear ICs is the 555 timer which was first introduced in early 1970 by Signetic Corporation giving the name as SE/NE 555 timer. This IC is a  monolithic timing circuit that can produce accurate and highly stable time delays or oscillation. Like other commonly used op-amps, this IC is also very much reliable, easy to use and cheaper in cost. It has a variety of applications including monostable and astable multivibrators, dc-dc converters, digital logic probes, waveform generators, analog frequency meters and tachometers, temperature measurement and control devices, voltage regulators etc. The timer basically operates in one of the two modes either as a monostable (one-shot) multivibrator or as an astable (free-running) multivibrator.The SE 555 is designed for the operating temperature range from – 55°C to 125° while the NE 555 operates over a temperature range of 0° to 70°C.

The important features of the 555 timer are :

• It operates from a wide range of power supplies ranging from + 5 Volts to + 18 Volts supply voltage.
• Sinking or sourcing 200 mA of load current.
• The external components should be selected properly so that the timing intervals can be made into several minutes Proper selection of only a few external components allows timing intervals of several minutes along with the frequencies exceeding several hundred kilo hertz.
• It has a high current output; the output can drive TTL.
• It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature, or equivalently 0.005 %/ °C.
• The duty cycle of the timer is adjustable with the maximum power dissipation per package is 600 mW and its trigger and reset inputs are logic compatible.

Voltage doubler circuit using NE555

Description:

The circuit diagram of a very simple voltage doubler using NE555 timer is shown here. Here IC NE555 is wired as an astable mutivibrator operating at around 9KHz. The base of the two transistors (Q1 and Q2) is shorted and output of the astable multivibrator (pin 3) is connected to it. When the output of astable multivibrator is low, Q1 will be OFF and Q2 will be ON. The negative terminal of the capacitor C3 will be shorted to ground through T2 and it will be charged to the input supply voltage. When the output of the astable multi vibrator is high, transistor Q1 will be ON and transistor Q2 will be OFF. The capacitor C4 will be charged to the voltage across capacitor C3 plus the input supply voltage (that is double the input voltage). This is how the circuit works.

This voltage doubler circuit can deliver only up to 50mA output current and above that current limit the output voltage will be dramatically reduced. The actual output voltage will be around 19V for a 12V DC input and also the output voltage will be a bit unstable. Anyway, for low current applications this circuit is well enough.

Notes:

The circuit can be assembled on a vero board.

The output current should not be allowed to exceed 70mA.

IC1 must be mounted on a holder.

Remote Control Circuit Through RF Without Microcontroller

Description

This is a simple type remote control by using RF communication without microcontroller. In this project a remote has been designed for various home appliances like television, fan, lights, etc. It gives lot of comfort to the user since we can operate it by staying at one place. We can control any of the appliances by using this remote within the range of 400 foots. In this project consist of two sections, transmitter (remote) and receiver section. Whenever we are pressing any key in the remote it generates the corresponding RF signals, and these signals are received by the receiver unit. ASK transmitter and receiver is used as transmitter and receiver. HT12E, HT12D encoders and decoders are used in this electronic circuit. The block digram of the whole circuit is given below.

USB Lamp Circuit

Description.

Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 Volt available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for the lamp, you can also use a 2 V torch bulb instead of LED’s. LED D3  indicates connection with USB port.

Line Follwer Robot-Using 2051 MC

This Robot uses two motors control rear wheels and the single front wheel is free. It has 4-infrared sensors on the bottom for detect black tracking tape, when the sensors detected black color, output of comparator, LM324 is low logic and the other the output is high.



Microcontrollor AT89C2051 and H-Bridge driver L293D were used to control direction and speed of motor

Circuit diagram of Robot.