Keypad
This logic circuit shows a keypad having 10 keys representing the numbers from 0 to 9. The input will be stored using the latching method. The input in decimal will be converted to binary numbers and will be displayed as decimals again.
Schematic Diagram:
Assembly Instruction:
The components to be used for the circuit are given on the figure above. For the switches, a push-button or tactile switch must be used. The small letter "a" in the diagram represents the 1st bit and "b" represents the 2nd bit and so on. The diodes used in the circuits are 1N4148 diodes. These diodes are fast switching diodes ideally used for these types of circuits. The diodes are placed in such a way that when pressing a certain number from 1-9, it will produce its equivalent binary number. For example, pressing 3 will give a value of 1 to "a" and "b" but none to "c" and "d" thus giving a binary number of 0011 - the equivalent binary number of 3. These values are then stored in memory using the latching method. To display the numbers in decimal form, the 74LS47 IC is used and connected to a 7 segment display. Pressing the number 0 will reset the circuit removing any memory thus giving a value of 0000 in binary or 0 in decimal form.
Pictorials:
