CSCE 211 Digital Logic Analysis and Design

Circuit 3

74LS47 and 7-Segment Display

Due: Thursday, November 18, 2010

• First, remove Circuit 2 from your board as follows: remove the 74LS04 and all its wires; remove the 74LS10 and all its wires.
• Leave Circuit 1 as is to generate and display binary codes 0000 to 1111.
• Make sure your DIP switch-LED circuits still work before continuing.  The 5th LED will be ON because its inverter has a “floating high” input.
• Insert the 74LS47 Decoder/Driver 2 pins to the right of the 5th LED. The diagram of 74LS47 is shown on the next page.
• Connect Vcc and GND to the 74LS47 chip.
• About 2 pins to the right of the 74LS47, insert seven 1K ohm resistors (at columns 42, 44, 46, 48, 50, 52, and 54), each spanning the gap.
• Make sure there are no “shorts” (contacts) between resistors on the top or bottom.
• Insert the 7-segment display 2 pins to the right of the last resistor.  The decimal point is in the lower right corner if your board is horizontal with the glued corner in the top left corner of the board.
• Connect either Pin 3 or Pin 8 of the 7-segment display to Vcc.  There is no GND connection for the 7-segment display.
• Now attach a wire from output Pin 13 (a) of the 74LS47 to one side of a resistor; attach another wire from the other side of the resistor to the Pin 7 of the 7-segment display.
• Test the a-segment by temporarily grounding the Pin 3 of the 74LS47.  This is called the “lamp test” (LT_Low); when grounded all connected segments will turn ON.  Using a temporary wire connection is faster than using the DIP switch signal that you will connect later.
• Continue to connect the remaining 74LS47 outputs (b-g) one-by-one.  Test each segment with the “lamp test” before continuing to the next segment.
• Use DIP switch #8 for the overall “lamp test” logic signal.  Remember to ground the “top” of the switch and connect a 1K ohm resistor from the bottom of the switch to Vcc.
• When the lamp-test signal is “0” all segments should be ON.
• Ignore the 74LS47’s “blanking” signals (pins 4 and 5); simply make no connection them.  (They are used to suppress leading and trailing zeros in large displays.)
• Finally, connect the DIP switch variables A, B, C, and D to the corresponding address signals (A₃-A₀) on the 74LS47.
• Test your circuit by disabling the lamp test signal (set it = “1”) and using DIP switch combination 0-9.
• Your 7-segment display will show the decimal equivalent of the binary numbers of the LEDs.
• Binary combinations 1010 through 1111 are not valid BCD codes; the 7-segment display gives unusual patterns.  Binary 1111 will turn all segments OFF.  
• A picture of finished Circuit 3 is shown here.

Check-off: Demonstrate that your circuit output on the 7-segment display is correct for all input combinations (i.e., from 0 through 9).

Report:  Show the very simple logical (not physical) diagram of the circuit for the 74LS47 and 7-segment display.  You must include pin numbers on your diagram.  For example, from pin (13-a) of the 74LS47, to one side of a 1K ohm resister, other side of the resister to pin (7-a) of 7-segment display.  You can print the following diagrams of 7-segment display and 74LS47 and include it with your report.  Use it to show connections from 74LS47 to display segments and DIP switch variables to the 74LS47.

Grading:  This circuit project will be due on Thursday, November 18, in class and will be worth 4 points toward your final grade. Your grade for each of the circuit assignments will be based on (1) demonstrating that your circuits work properly and (2) a short written report that provides a few details about the circuits.  You will demonstrate your circuits and turn in your report on your check-off day.

Connections for 7-Segment Display  

Shown in “horizontal” position with decimal point (DP) at lower right