Johnson Counter

1. Johnson Counters Jatinder Kumar chaurasia (11508173) M.Revanth (11503559) O.Purnachandra (11504239)

2. Introduction to counters Counters –count no of times a particular event occurred A counter used two or more flip-flop depending upon the no. of bits required There are two types of counters: 1.Asynchronous counter 2. Synchronous counter Asynchronous counter used a single clock at the first stage Synchronous counter ,all flip flops are clocked together with a common clock pulse

3. Johnson counter Johnson counters also called twisted ring counters It is a modification of ring counter The only difference is that instead of last output( Qd ) back to the input( Qa ) the not of (^ Qd ) is connected to the first input.

4. Circuit diagram of 4 bit Johnson counter

5. Truth table of Johnson counter

6. Timing diagram of 4 bit Johnson counter

7. Uses of Johnson counter Used in walking LEDs Used to convert square waves to sine waves

8. Conclusion Johnson counter is a modified ring counter where the output from the last flip-flop is inverted and feed back to the input of first flip-flop The main advantage of Johnson counter is that it only needs half the no. of flip flops compared to the standard ring counter of same mod If we use n flip-flops then it is known as 2n bit Johnson counter or mod-2n Johnson counter

9. Components used for making 4 bit Johnson counter 7474-IC(D-flipflop):2 5 resistors(100 ohm) 5 LED bulbs One battery(9v) Wires(20m) One 555 timer( bistable multivibrator used as a clock)

10. Thank you