CSCE 211: Circuit No. 3

74LS47 and 7-Segment Display

 

  • 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 F LED will be ON because its inverter has a “floating high” input.
  • Insert the 74LS47 Decoder/Driver 2 pins to the right of the DIP switch.
  • Connect Vcc and GND to the 74LS47 chip.
  • About 2 pins to the right of the 74LS47, insert seven 330 ohm resistors, each spanning the gap.
  • Make sure there are no “shorts” 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 battery pack in the top right corner of the board.
  • Connect either Pin 3 or Pin 8 of the 7-segment display to Vcc.  There is no GND connection.
  • 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 the “lamp test” (LT_Low); when grounded all connected segments will turn ON.  Using a temporary tire 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 1.0 K 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. (See data sheet below).
  • 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.

 

Circuit 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.  Please print and include the next page with your report.

 

 

Connections for 7-Segment Display (LSD5061)

 

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