This circuit decodes 4-bit binary and turns it into 16 separate outputs through AND &
NOT logic gates.
Explanation of logic gate input values on the right half of the circuit to create a high output. Top to bottom:
top two AND gates:
A: high, B: high
C: high, D: high
four NOT gates:
inverts A, B, C and D
top three AND gates below NOT gates:
D: high, C: low
C: low, D: low
D: low, C: high
bottom three AND gates below NOT gates:
B: high, A: low
B: low, A: low
B: low, A: high
All other AND gates use output values of logic on the right half of the circuit to light output LEDs.
If you want to build this circuit on a breadboard, I recommend replacing the 1 uF capacitor with a 100 uF capacitor to change the timer pulse to about 1.89 hertz instead of 189 hertz to create a visible pulse.
Parts you will need:
5v regulated power source
one NE555 timer
one 74HC193 4-bit binary counter
six 74HC08 quad 2 input AND gate
one 74HC04 hex 1 input NOT gate
one 1 Kohm resistor
one 3.3 Kohm resistor
one 10 nF nonpolarized capacitor
one 1 uF polarized capacitor
one SPDT switch
one normally closed push button
sixteen 4.5V 20mA LEDs
The SPDT switch is for selection between a random output or visible counting. The pushbutton is for stopping the count in visible counting mode or for revealing a random number in random output mode.
To gain a more thorough understanding of this circuit you can print it out and trace each wire with a different colored pencil to see where they lead and what they do.
