Lab-11, Flip-Flop and Counters

Physics U371/372, Electronics for Scientists, Fall 2007

Don Heiman, Northeastern University (11/12/07)

 

You will need:

·                    prototype board (with 5V power supply)

·                    jumper wire kit

·                    chip extraction tool

·                    patch cords

·                    function generator

·                    two 74112 flip flop chips

·                    three LEDs

·                    switch

 

 

I.  Truth Table

Study the specifications of the 74112 (or similar) packaged JK flip flop. Remember to connect each input (R,S,J,K) to either ground or +5V, and set S=R=1 for all measurements.

 

1.  Explain the features of the device.

2. Study its performance using the TTL output on the function generator set to f<1 Hz. Work out the truth table for changing inputs J, K, and CK, by using LEDs on the inputs and outputs.

 

 

II.  JK Flip Flops in Series

Connect Q1 to J2 and K2. Set J1=K1=1 (via 1 kΩ resistor to +5V).

 

1. Connect CK to low frequency and study output. Explain.

 

 

III.  Roll of the Dice

Build a binary counter with three JK flip flops. Use LEDs on the three outputs to indicate the binary equivalents of the decimal numbers 0 to 7. Connect CK1 to low frequency (~1/2 Hz).

 

1.  Verify the correct counting. Show this to your instructor.

2.  Now connect CK1 to the oscillator via a switch.  Use the switch to “roll the dice.”

At what frequency can you no longer predict your roll?

3.  How could you prevent the number 0 from appearing? Draw the circuit. You can build the circuit if you choose.