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I was wondering what's wrong with my Proteus schematic.

This schematic is supposed to show the frequency in Hertz on the display but instead only three zeroes are displayed.

Is there any component that is missing or needs to be added?

enter image description here

So far my LEDs are now somehow displaying numbers but it does not precisely display the exact frequency number. It is always stuck at 999 or 332 on the display.

enter image description here

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  • \$\begingroup\$ You have the enable inputs of your 74LS75 chips tied low. \$\endgroup\$
    – Dave Tweed
    Commented Jul 28, 2022 at 11:08
  • \$\begingroup\$ Thank you very much sir! \$\endgroup\$
    – DyBancs
    Commented Jul 28, 2022 at 11:22
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    \$\begingroup\$ For future reference, set the clock source to a low frequency (like 1Hz) and watch the (red/blue, high/low) states of the pins. You'll want to have the chip datasheets open to verify each pin is doing what it was designed for. \$\endgroup\$
    – rdtsc
    Commented Jul 28, 2022 at 13:00
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    \$\begingroup\$ @DyBancs - Hi, Your "answer" (which wasn't an answer to your original question, and therefore should not have been posted in the "Your Answer" box) has been added to the question as an edit i.e. an update instead. Unless you are writing a full & final new answer, unlike any existing answers from other people, to your own question (i.e. unless you have solved the problem yourself, with no further help needed) please don't use the "Your Answer" box below. Instead, you should edit the question to add new information. See the tour and help center for more rules. Thanks. \$\endgroup\$
    – SamGibson ♦
    Commented Jul 28, 2022 at 13:12

1 Answer 1

Reset to default
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You appear to be clocking both the two set and reset inputs on all the 74LS90 counter chip. This will confuse the logic and possibly keep the counter permanently set to zero.
Similarly you have tied all the enable pins of the 74LS75 latches to ground which will permanently disable them.
It looks as if you have interchanged the signals to these two sets of inputs. You meant to clock the latches and disable the set and resets.
Have a look at this tutorial web page which shows the correct connections for the 74LS90 (they should all be tied to 0V for your applications) and gives a lot more useful information. Also Googling "BCD counter to 7 segment display" will give you dozens of useful tutorials.

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  • \$\begingroup\$ But for a frequency counter, you do need to be able to reset the counters at the beginning of each sampling cycle. \$\endgroup\$
    – Dave Tweed
    Commented Jul 28, 2022 at 12:01
  • \$\begingroup\$ @DaveTweed Agreed, I was only looking at the basic design of the counter / latches / decoder / display. Even so, clocking all 4 set and reset pins simultaneously, as the schematic seems to be doing is still wrong. It should be done from a separate source defining the sampling cycle, and to only one reset input per counter. \$\endgroup\$
    – Peter Jennings
    Commented Jul 28, 2022 at 14:07

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