Decoupling capacitor for timer and ATTiny85 (was Noises / Electric Peaks)

Hello guys,
I developed a list of different component, in Arduino or simple electronic and now I’m experiencing issues like “restart” or false signals along the signal cables.

For example, I’ve got a simple timer, it make a countdown and it is composed by a button, a 4 digits 7 segments display and a ATTiny85. I attach simple schematic view.
The “start” signal has a pull-up resistor and the timer restart when the signal goes down.
The “stop” signal has a pull-down resistor and the timer stop when the signal goes up.

Yesterday, the timer restarted autonomously, even if no-one made anything (no-one pressed the restart button). Cable that bring the signal down is, I think, 5cm long.

The power supply is built as following

  • AC 220 to DC 12V - with a power supply 1A
  • DC 12V to DC 5V - power regulator

We noted something similar with another tool where the cable is longer (quite 2m): a Raspberry Pi should send a high signal along the cable and when we have a current spike in the flat (we turn the light on or we turn on a drill or - it happen - when just we connected the drill to the plug), the cable bring a floating high value alone…

Could someone give me some ideas on out to fix this issues?

Can you hand sketch a complete diagram - I see no button or resistors, or any ground or Vcc connection to the switch logic, so it cannot be complete.

There is also no decoupling capacitors shown. If you have none then that is the cause of your problem.

You are all right!
That was the sketch of the circuit I printed in Fritizing, but button and other parts are not directly connected to the PCB but through some cables.

The capacitor is connected closest to the 5V source then between the VCC and GND of the ATTiny.

Attached the completed sketch.

A 10nF capacitor is a bit small, is it ceramic? It has to be.
Also I would add a 47uF in parallel with it.

Finally the pull up should be dropped from 10K to 1K for extra immunity.

Yes, it's a ceramic cap. Another one, 47uF 25V Electrolytic Capacitor?
Good to know for the pullup resistor...

Yes that is the only type of cap for this sort of value.