From childhood You always saw blinking of lights..right??And after getting older and studying electronics or computer hardware basics you always saw the term "clock Pulse" ...right?? So this clock pulse is nothing but a square wave.
Now a rectangle wave as a 555 timer can generate can also be a square wave for a particular values of resistors.We will see next.
See the picture and you can understand what is a square wave. It is due to that nature the LED light, if connected, always blinks at a particular frequency.
Now this clock pulse is very essential for counters, JK,RS,D,T flip flops and many other micro controllers too. So here I will be presenting a square wave generator using the very very popular and super cheap 555 timer.This circuit can blink a LED. This circuit will come in handy while dealing with flip flops ,counters,etc.That's why I build this, so that this can be ultra portable and super cheap.
Step 1: Parts Required
1 555 timer IC and 8pin socket
2 1MEG ohm variable resistor
3 2 Piece 1K ohm resistor
4 1uF capacitor (polarised)
5 LED or multimeter or oscilloscope (optional,just for testing)
6 9 V battery and clip
7 perfboard and solder kits
9. A PN diode( in case if you want a pure clean square wave....if rectangular is OK ..then it is not necessary)
Step 2: Understanding Circuit and Building on Breadboard
Now look at the circuit above. The 555 timer is in astable mode now.At this mode it can generate rectangular/square wave output. The duty cycle of this wave cannot be less than or equal to 50%. It is always greater. As always you can find more info over the net.Now we can change the resistance R2 and can change the frequency. So I have attached a variable resistance like 1MEG here. So by attaching this value of varistor we can get frequency ranging from 0.721Hz--1.443KHz at the output. You can use the formula given in the picture for finding that frequency. Now the on time and off time can be calculated by the formula given in the picture so for Ra/R1 much less than Rb/R2, you can take it as a square wave.So as an optional you can replace Ra/R1=1K by 1K varistor.Or best for getting a nice clean square wave( if necessary) then add a PN diode(eg. 1N4007 or anything else) parallel to R2 or Rb with the N side connected to the positive terminal of C. The capacitor at pin 5 is to reduce noise.
Now following the above circuit, build this on breadboard. You can use a multimeter or LED to test the output stage. If it is all right the LED should blink for the on time period .If not then rotate the varistor clockwise or anticlockwise and then you will get your result( since if the varistor was set initially at a value such that the o/p frequency is Khz range then you cannot see the led blinking). Be careful about capacitor polarity(longer one is +ve).Still if it is not blinking carefully build the circuit again.
Step 3: Finally.....time for Soldering
For keeping this circuit as permanent and portable you need to solder all components as in the circuit diagram.I have done it as in the picture above.You may position your components as per your convenience. After soldering test it again with a multimeter or led or oscilloscope. So now you are done finally and you can use it in any counters,flip flops or microcontrollers....