Is it possible 7490 is skipping number on 7 digit display?

Hello guys. I am pretty sure this is my fault but I have wired it many times by far and I am getting this strange behaviour from my circuit. So, just checking if anybody have had same problem before.

I am making a little test with the 7490 (SN74LS90N) and the 7445 (TC74HC411P) ics to create a decade counter.
So basically I am using the BLINK example on an arduino board, except that it doesn't go LOW for more than 10 millis.

It works. But it counts 0, 2, 3, 4...9, 0, 2, 3... skipping the number 1!
I have checked the 7445 connections, and when I change the values by hand, it can display correct numbers on the 7 digit display. Also, I have placed some leds on each output of the 7490 to read the binary, and it is really skipping the number 1 for some reason.

wiring seems to be ok, but I can redo it more a couple of times if needed. It is just that I couldn't figure out why it is working only 90% correctly...

Any clue?

Thanks in advance,


Post your code, maybe? And maybe a schematic?

Is it possible 7490 is skipping number on 7 digit display?

No it is not. Chips do not make mistakes people do. So the mistake in in the hardware of software. Once we see that we stand a chance of finding yours.

You’ve missed out decoupling the chip haven’t you? Sounds like a classic glitch,
switching from 0 to 1 causes a rapid drop in current(*), no decoupling and the supply
bounces up and triggers a second clock pulse.

Add decoupling and that current pulse is absorbed happily in the capacitor for only
several mV of bounce in the short term.

The most likely 7-segment sequences for glitching due to inadequate decoupling
are 0 to 1 (4 segments switch off) and 7 to 8 (4 segments switch on).

(*) perhaps +100mA in < 5ns - more than 20A/us