I am doing a simple 7 segment display circuit using ne555,74ls90 and 7447 ic I connected everything up but the number run 0,2,4,6,8 and did not go to 1,3,5,7,9 and continue... what is the main problem that caused this? This is my schematic diagram enter image description here enter image description here

  • 5
    \$\begingroup\$ That schematic is far too small to read. \$\endgroup\$
    – Hearth
    Jul 29, 2018 at 14:04
  • \$\begingroup\$ goo.gl/images/ND4uoK this is the clearer version of schematic diagram \$\endgroup\$
    – james
    Jul 29, 2018 at 14:13
  • 1
    \$\begingroup\$ Is pin 7 of the 7447 connected to pin 12 & 1 of 7490? \$\endgroup\$
    – D Duck
    Jul 29, 2018 at 14:30

2 Answers 2


There are two possible scenarios that spring to mind. If you look at the modified circuit below with the pin names on, it'll be clearer: -

enter image description here

For it to count only even numbers I suspect that the QA output is not reaching input IA of the 7447. This means that IA on the 7447 is probably high or low and so it only registers changes that are multiples of two and produces odd or even numbers. You could test this by connecting IA to 5 volts to see if it now counts only odd numbers.

The other possibility is that you have QA and QD outputs swapped over but that would then lead to counting odd numbers once you have got past a count of 8.

  • 1
    \$\begingroup\$ Wouldn't an unconnected one's bit lead to odd numbers? Being stuck at ground would be more consistent with the observed behavior. \$\endgroup\$ Jul 29, 2018 at 16:02
  • \$\begingroup\$ Ooops yes you are quite correct @ChrisStratton \$\endgroup\$
    – Andy aka
    Jul 29, 2018 at 16:19

Possibly you're getting double counting due to lack of bypass capacitors on any of the chips (particularly the 555 and the 'LS90).

Your power supply schematic looks a bit questionable as well. The grounds should be tied together and Vcc fed by a regulated 5V.

Of course there could be a bad or incorrect interconnection but that's hard to diagnose remotely. An open to the 'A' input of the 7447 would lead to it counting in odd numbers, so that's not it.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.