Easy to build LED Light Flasher

This is a simple LED flasher project that uses a CMOS 74C04 Integrated Circuit to alternately ON and OFF two LEDs that are connected in parallel. The Hex inverter MM74C04 from Fairchild Semiconductor has a wide operating power supply voltage range from 3V to 15V DC. It has a typical low power consumption of 10nW/package and has high noise immunity. It is back to back compatible with the standard 74 logic family which is freely available in the market. All its inputs have diode clamps to VCC and GND which protect them from damage due to electrostatic discharge.

Schematic Description



The schematic above shows the simple configuration of the project. It uses two inverters U1A and U1B to form an oscillator configuration where the frequency of the oscillation is given by :

f = 1/[1.4RC]

= 1/[1.4(10 M Ohm)(0.1uF)]

= 0.7 Hz

The square wave frequency of 0.7 Hz is used to feed the input of U1D which is used as a buffer circuit. At the same time, the other inverter U1C gets its input from pins 2 and 3 of U1. With this configuration, when U1D output is high, U1C output will be low and vice versa. In this way when LED1 is ON, LED2 will be OFF and this will alternate at a frequency of 0.7Hz.
The current that goes through the LED is given by:

I = (9V-7V)/510 ohm

= 14mA


It is assumed that the voltage drop across each diode is 2V when it turns ON. One can experiment with the oscillation frequency by changing the values of R1, R2, R3, and C1. The brightness of the LEDs can also be changed by changing the values of the resistor R4. However, always ensure that the current through the LEDs is not exceeded or else the LEDs will be damaged.


LED Light Flasher Parts List

Basic usage of a 555 timers!

Introduction
Timer circuit has been used in many projects and there are basically 2 types that are used these days. One of them is the use of analog RC circuit where charging of the capacitor circuit determined the T(time) of the circuitry. This type of circuitry has larger tolerance and is used in applications where the T is not so critical as the T is affected by the tolerance of the RC components used.
The other is the use of crystal or ceramic resonators together with microprocessor, microcontroller or application specific integrated circuit that need higher precision T in the tolerance of up to 5 ppm (parts per million).



555 IC
One commonly used circuit is the 555 IC which is a highly stable controller capable of producing timing pulses. With a monostable operation, the T(time) delay is controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor. The application of this integrated circuit is in the areas of PRECISION TIMING, PULSE GENERATION, TIMING DELAY GENERATION and SEQUENTIAL TIMING.
A typical 555 IC block diagram is as shown below.





Monostable Operation
Figure below shows the monostable operation of a 555 IC.





In this mode, the device generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to pin 2 falls below Vcc/3 while the its output is low, its internal flip-flop turns the discharging transistor Tr off and causes the output to become high by charging the external capacitor C1 and setting the flip-flop output at the same instant. The voltage across the external capacitor C1, VC1 increases exponentially with the time constant T=RA*C1 and reaches 2Vcc/3 at td=1.1RA*C1. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RA*C1, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RA*C1 controls the output pulse width. When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging transistor Tr on. At this time, C1 begins to discharge and its output goes to low.
Astable Operation




An astable operation is achieved by configuring the circuit as shown above. In the astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multivibrator. When its output is high, its internal discharging transistor Tr turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C. When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing its output to become low. This in turn turns on the discharging transistor Tr and the C1 discharges through the discharging channel formed by RB and the discharging transistor Tr. When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging transistor Tr turns off and the VC1 rises again. The frequency of oscillation is given as below.

Phone call detector circuit!

This circuit is quit simple, its uses a 555 timer ic set as a monostable multivibrator to prolong the detector circuit output... I have tried it my self and it worked perfectly,, hope you like it!

Parts list:

R1____________100K   1/4W Resistor
R2______________3K9  1/4W Resistor
R3______________1M   1/4W Resistor

C1,C2_________100nF   63V Polyester Capacitors
C3____________220µF   25V Electrolytic Capacitor

D1______________LED  Red 10mm. Ultra-bright (see Notes)
D2___________1N5819  40V 1A Schottky-barrier Diode (see Notes)

Q1____________BC547   45V 100mA NPN Transistor

IC1____________7555 or TS555CN CMos Timer IC

L1_____________Sensor coil (see Notes)

B1_____________1.5V Battery (AA or AAA cell etc.)

A simple yet useful electronic touch switch which can be used for intruder alarm!

Touch Switch And Delay Circuit Using 555 Timer IC

Touch Switch And Delay Circuit Description

In this simple touch switch circuit, the 555 timer is configured as a one shot multivibrator that is triggered by touching the touch terminal.
In this monostable mode, the timer generates a fixed pulse of about 4 seconds whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C2 and setting the flip-flop output at the same time.
The voltage across the external capacitor C2, VC2 increases exponentially with the time constant t=R3*C2 and reaches 2Vcc/3 at td=1.1R3*C2. Hence, capacitor C2 is charged through resistor R3. The greater the time constant, the longer it takes for the VC2 to reach 2Vcc/3. In other words, the time constant R3*C2 controls the output pulse width. When the applied voltage to the capacitor C2 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C2 begins to discharge and the timer output converts to low. In this way, the timer operating in the monostable repeats the above process.
To increase the time of the delay from 4 seconds, the value of R3 and C2 need to be increased. Similarly, to decrease the output time delay, the value of R3 and C2 need to be reduced.
The output from the 555 timer can be used to drive a transistor which in turn can drive a delay to control device like lamp, and other equipments.




Parts List




Source : Extracted from Popular Electronics April 1996, By Charles D. Rakes

 

Simple Electronics

This page is to give you insights how to create a simple yet useful electronic devices. the post will start next week so stay tuned!