One of the most popular and widely used IC’s of all the time. 555 Timer used in many electronic devices, ranging from simple toys to more even spacecraft.
555 Timer applications
555 Timer IC is used as Tone Generator or a Alarm Generator. It is used as a Flip-Flop element, Digital Logic Probes, Lamp Dimmer, LED Flasher, etc. Here in the given below a Piano and a Beatbox is shown using a 555 Timer IC.
Why 555 Timer
555 Timer IC is very cheap, popular, versatile of it’s multi-functionality and useful Precision Timing Device. 555 Timer IC generates output in a digital form 0 or 1.
Here 1 means HIGH signal or Power Supply and 0 means LOW signal or Ground.
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Why is it called 555 Timer
The 555 Timer got it’s name from three 5KiloOhm resistors connected in series that are used in it’s Voltage Divider Circuit.
555 Timer Pin Diagram
PIN 1 is Ground Pin, Pin 2 is the Trigger Pin, PIN 3 is Output Pin, Pin 4 represents Reset Pin, Pin 5 is the Control Voltage, PIN 6 is Threshold, PIN 7 is the Discharge PIN and PIN 8 represents Power Supply or Vcc.
555 Timer Internal Architecture
555 Timer is divided into 5 parts. First part is voltage divider circuit, second comparator block, third flip-flop circuit, fourth discharge circuit and last output driver circuit.
Voltage Divider Circuit
Voltage divider circuit is the first block of the 555 Timer IC. In Voltage Divider Circuit three 5KiloOhm resistors connected in series that are connected from PIN 1 to PIN 8.
Power supply or Vcc is divided into two parts 2/3 Vcc and 1/3 Vcc.
Comparator
Comparator is the second block of 555 Timer IC.
If voltage in Non-Inverting Terminal / Positive Terminal is greater than the Inverting terminal / Negative Terminal (It means V1 is greater than V2) then the output will be HIGH / 1 / VCC.
If voltage in Non-Inverting Terminal / Positive Terminal is lesser than the Inverting terminal / Negative Terminal (It means V1 is lesser than V2) then the output will be LOW / 0.
Flip-Flop
Output of the comparator is connected to S-R Flip-Flop. So, S-R Flip-Flop is the third block of the 555 Timer.
In S-R Flip-Flop Set input sets the output Q HIGH/1 and Reset input resets the output Q back to LOW/0.
If inputs Set(S)=1, Reset(R)=0 then the outputs will be Q=1 and not(Q)=0. Now if inputs Set(S)=0, Reset(R)=0 then the outputs will be Q=1 and not(Q)=0, no changes occured.
If inputs Set(S)=0, Reset(R)=1 then the outputs will be Q=0 and not(Q)=1. Now if inputs Set(S)=0, Reset(R)=0 then the outputs will be Q=0 and not(Q)=1, no changes occured.
Output Driver & Discharge Circuit
Output Driver Circuit and Discharge Circuit is the last block of the 555 Timer IC. In Output Driver circuit, an inverter is connected with PIN3.
Inverter is a device that gives the outputs a voltage representing the opposite logic-level to its input. If input is HIGH / 1 then the output will be LOW / 0. If input is LOW / 0 then the output will be HIGH / 1.
In Discharge Circuit, a transistor is connected with PIN7. So, PIN7 is the Discharge Pin of the 555 Timer.
If inputs Set(S)=1, Reset(R)=0 then the outputs will be Q=1 and not(Q)=0. We can see that not(Q) is connected to base of the Discharge Transistor and also connected to the Inverter of the Output Driver Circuit. Discharge Transistor is in OFF state and output of PIN 3 is HIGH because not(Q)=0
Now if inputs Set(S)=0, Reset(R)=0 then the outputs will be Q=1 and not(Q)=0, no changes occured.
If inputs Set(S)=0, Reset(R)=1 then the outputs will be Q=0 and not(Q)=1. Here Discharge Transistor is in ON state and output of PIN 3 is LOW because not(Q)=1.
Now if inputs Set(S)=0, Reset(R)=0 then the outputs will be Q=0 and not(Q)=1, no changes occured.
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