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Why doesn't it show anything on the seven-segment displays when it's running? It also shows grey areas at the connections.

  • \$\begingroup\$ difficult to guess ... maybe you did not connect the 7 segment displays to anything \$\endgroup\$
    – jsotola
    Sep 28, 2022 at 3:17
  • \$\begingroup\$ Are you sure that 7 segments common pin is to be connected at ground and not at power supply 5V? What is the "driver"? \$\endgroup\$
    – Antonio51
    Sep 28, 2022 at 8:59
  • \$\begingroup\$ What type are the seven-segment displays, common anode or common cathode? \$\endgroup\$ Sep 28, 2022 at 9:05
  • \$\begingroup\$ You need to start the simulation. In this screenshot, the simulation isn't running as you have no red/blue/grey logic indicator boxes on the IC pins \$\endgroup\$
    – MCG
    Oct 5, 2022 at 7:20

1 Answer 1


Instead of DC sources with U6 and U7 use POWER terminal. Although the DC sources work as well but you might have forgotten to set the voltage. Anyway, POWER terminal can be found under TERMINAL group to the left. It has an up arrow symbol, and is a 5V source for logic components.

Plus, D1 LED loads the output of the topmost OR gate (U2-A) so either use a logic probe or drive the LED with a suitable current sense resistor.


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