Description

RGB Bulb Using NE555 Timer

Introduction

An RGB bulb is made up of three individual LEDs: red, green and blue. The intensities of these LEDs are varied to generate lights of different colours or shades.The main objective of this project is to produce different light colours with the help of NE555 timer IC.

Circuit

It is built around 230V AC primary to 12V-0-12V, 500mA secondary transformer (X1), a 5V regulator IC 7805 (IC1), three NE555 timers (IC2 through IC4), red, green and blue LEDs (LED1 through LED3), and a few other components.

Operation

• When the output of IC2 (NE555) is high, capacitor C3 charges through 1-kilo-ohm resistor, diode D3 and part of VR1 (say, VR1A). When capacitor voltage reaches 2/3Vcc, the output of IC2 goes low.
• Now capacitor C3 discharges through the other part of VR1 (say, VR1B) and D4 to 1/3Vcc.
• So sliding VR1 towards left decreases VR1A value, and hence charging time, ‘on’ time and duty cycle. At the same time, VR1B increases, which increases the discharging time as well as ‘off’ time.
• On the other hand, turning VR1 towards the right position increases VR1A, and hence the charging time, ‘on’ time and pulse-width. But as VR1B is decreased, ‘off’ time decreases too. Thus, pulse-width can be varied by sliding VR1 towards its sides. When this PWM signal is applied to the LED, the average voltage applied to the LED varies. This varies its intensity and brightness. Thus the three potmeters vary the brightness of red, green and blue LEDs.
• By varying a potmeter from minimum to maximum, the colour intensity of the respective LED varies from 0% to 100%. For example, if VR3 is turned towards maximum value, the blue LED intensity become almost zero Now varying VR1 and VR2 will produce different colours like red, green, yellow, lime, orange, and various shades of green and red.
• Similarly, set VR2 to maximum value in order to turn off the green LED. Then vary VR1 and VR3. This will generate red, blue, magenta, violet, and various shades of red and blue. Thus, by varying these three potmeters, many different colours can be generated. If the three LEDs are carefully placed inside an incandescent bulb glass housing, it becomes an RGB bulb!