Monday, June 17, 2013

LED Flasher Using 555 Timer IC - Hobby Electronics

Good Evening Everyone. Hope you guys are doing great. Today I'm going to show you how to make a very simple LED flasher using a very common IC the 555 timer IC. I came across this IC long ago. Maybe 8 years or so. This IC is awesome for making small projects like LED flashers even large lamp flashers, or even making a timing circuit or a frequency generator! So let's dive in.

What is a 555 Timer IC?


555 timer IC is an Integrated IC that can be used in pulse generator, timer & oscillator applications. It can provide time delay, it can work as a oscillator or even a flip-flop. It's main positive sides are easy to use, very cheap & good stability. It is an analog IC. It can also be found as digital version which is called 7555. This IC can be used in three different modes. Monostable mode - where it works like a one shot weapon, Astable where it runs freely & Bistable where it can run as a flip-flop. I will talk about 555 & digital IC's later. Now lets look at the diagram.



How does they look like?



NE555 on the left and 7555 on the Right

The left one is the NE555 the analog one, & the right one is the HA 7555 which is the digital one. Digital one is more accurate & has higher voltage range but reverse polarity can destroy the chip easily. 7555 one is the CMOS one.


Pin Configuration


Pin 1: GND - Ground reference voltage, this is where usually 0V line is being hooked up.

Pin 2: TRIG - Voltage below 1/3 of +Vcc to Trigger the pulse. 

Pin 3: OUT - This is the output pin. Approximately 1.7V below the +Vcc or GND.

Pin 4: (invert)RESET - A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR(Pin 6). It is an active low pin. It interrupts the timing interval at output.

Pin 5: CTRL - Provides access to internal voltage divider. By default 2/3 Vcc.

Pin 6: THR - Pulse or timing interval ends when this voltage(voltage at THR) is greater than control(Voltage at CTRL). 


Pin 7: DIS - Open collector output to discharge the capacitor. It is in phase with output.



Pin 8: +Vcc - Positive supply voltage.
 

Diagram





Frequency Equation:

Description:

In this post I'm not going to go into the in depth mechanism of this diagram. I will do that on a later post. This diagram is simply an example of 555 running on Astable mode. Output will be pretty much a square wave that will drive the two light emitting diodes at two different time. You can use single LED too. Use calculated values for R1, R2 & C. You can put two variable Resistors just for experimenting. Better to provide a regulated power supply that I have already shown & you are all set. 


Datasheets of 555 , 7555, 556, 7556.


Take care everyone & keep experimenting.

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