I have designed a circuit to display the 2-digits data using two 7447 decoder. The design is shown below. enter image description here

I have two outputs, O1 and O2. O1 represents the ones digit while O2 represents the tenths digit. However, when I simulate the waveform, it is not correct partially. For example, '63', the '6' seems like is not a correct output. O1 has no issue, but O2 always has problems. How to solve this?

enter image description here

Thank you.

  • \$\begingroup\$ I don't know anything about your simulator, but you are aware that the 7447 is open collector and is active-low? \$\endgroup\$ Jun 27, 2023 at 1:36
  • \$\begingroup\$ I know 7447 is active-low decoder, that's why output 0 will light up the respective segment. \$\endgroup\$
    – CJ. T
    Jun 27, 2023 at 1:38
  • \$\begingroup\$ Just wanted to be sure, because I've no idea how your simulator works with such devices. Your connection looks right on first glance. So I suspected the simulator. \$\endgroup\$ Jun 27, 2023 at 1:39

1 Answer 1


You should have Y6 connected to C on the lower 7447. Otherwise the maximum you can display is 39 base ten.


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