Hi,

I have a circuit that utilizes a 74161 4-bit counter. The 1hz clock signal for this counter originates from a 555 timer. The output of the counter goes to logic gates, ultimately controlling the letters on three 7-segment displays.

Initially, the circuit functioned flawlessly when powered by a brand-new 9-volt battery with a voltage regulator. However, it now has frequent glitches. sometimes the displays get stuck on the first set of letters, other times they operate normally, and sometimes they switch super fast.

I connected the circuit to a 5V power bank, which resulted in a 50% less glitches. However, powering the circuit directly with a 5V wall adapter almost eliminated the problem, with glitches occurring only once in like 50 operations.


I use 10uf capacitor for the 555 timer and that's it. I've searched online and I guess there's some noise in my input, so what do you think?

 

Hi Max,
Add decoupling capacitors on the power line, say 100uF and 100nF
E

 

Hi Max,
Add decoupling capacitors on the power line, say 100uF and 100nF
E

Thanks for commenting.
Would you elaborate on the "Power lines" part? ditched the regulator and directly using the 5v powerbank.

 

Hi Max.
The +V supply and the 0V of the supply, on the board near the 555
Do you follow OK?
E

Update: @maxdha
Check 555 Pin #4 Reset, should be on +V connection, not open circuit.

 

Hi Max.
The +V supply and the 0V of the supply, on the board near the 555
Do you follow OK?
E

Update: @maxdha
Check 555 Pin #4 Reset, should be on +V connection, not open circuit.
View attachment 309772

Wow that worked! All 3 glitching disappeared!!! Apparently pin 4 need to be plugged to avoid false triggering..
Thanks so much for your help<3
You just saved me from a bunch of headaches.



,,

 

In general, never leave inputs floating. There are exceptions where it is okay to do so, but they are few, far between, and clearly spelled out in the data sheets.

 

As stated above,

1) Never leave inputs floating.
2) Always install 100nF capacitors between Vcc and GND as close as possible to all IC pins.
3) Always install 10-100μF capacitor across Vcc and GND as close as possible to LM555 timer IC pins.