Encoder Lab

Objective:

Build a Decimal-to-binary encoder circuit
Understand the functionality of the keypad
Understand 74147 IC priority encoder.
Learn how to use the debugger board.

Task:

In this lab you will make a decimal to binary encoder. Use the keypad as your input and the debugger board to display your output.

Part list:

One SN74LS147N
One 16key Keypad
Two Resistor Array (10x-1-102)
Debugger board

Background:

Encoder Chip

We will use the 74147 IC as the encoder in our circuit. This encoder is called a 0-line-to-4-line priority encoder by the manufacturer. The 74147 takes the selected input and outputs the corresponding 4-bit binary number. See the datasheet for more information. http://rabbit.eng.miami.edu/info/datasheets/

74147 decmial encoder
74147 function table 74147 schematic diagram

Hexadecimal Keypad

A keypad provides an easy input device to a digital circuit. It consists of several switches, one under each key, which have one of their two poles in common. To use a key to send a HIGH (1) signal, one must connect the common pin to 5 volt supply and put a resistor to ground from each of the other pins, as with the DIP switch package. Using 16 individual resistors to do this it would be rather tedious, so we will once again use the resistor arrays. The particular resistor array which we will use has several resistors in it which all have one end in common.

However; in some cases, such as in this lab, you will be using the keypad for input to devices which use active low inputs. This means that you will want a key pressed to give a low output on the corresponding line. To do this, simply switch the common connections of the keypad and resistor array mentioned above. This means you will connect the common pin of the keypad to ground and the resistor array to Vcc (+5V).