i am having a problem with this circuit : enter image description here

Basically, the ATtiny85 waits for a signal on BS coming from a momentary button, when the button is pushed, it puts HIGH on the pin called Load to power up the RF-Nano.

This is part of the PCB used :

enter image description here

The circuit works only if i touch with my finger the two pins which are Load and Button Signal (BS), and works only if they are touched at the same time otherwise it does not work. I have a ground plane on both bottom and top layer one the whole pcb.

Thanks for your help and excuse my english.

  • \$\begingroup\$ I forgot to mention that the circuit works perfectly fine if power is supplied from Arduino Uno 5V pin and GND pin. \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:11
  • \$\begingroup\$ How is it not working? \$\endgroup\$ Aug 17, 2021 at 13:40
  • \$\begingroup\$ It is just not powering the RF-Nano. \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:41
  • \$\begingroup\$ Can you check with your multimeter whether the ATTiny85 is outputting the Load signal, if it's supposed to do that? \$\endgroup\$ Aug 17, 2021 at 13:46
  • \$\begingroup\$ Thanks for the help. i got it working by using a 10uF capacitor as Tony suggested \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:49

1 Answer 1


This is a common problem with a noisy PS and input is unbalanced with conducted and radiated noise.

Putting your finger adds a large common mode shunt capacitance (your body) in series with your finger tip which absorbs the radiated CM noise.

The solution depends on minimizing input wire loop area and shielding the supply and wires to reduce CM noise. If this is not sufficient a cap to earth ground or ground wire to supply earth ground and/or a CM pi filter to power is required.

  • \$\begingroup\$ Thanks for your reply, i tried to use a capacitor between my 5V and Gnd (100 nF) and it really does not work, i would like also to know how it is possible that it works fine if power is supplied using an Arduino Uno, is the 5V of Arduino is more stable and filtered well ? \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:37
  • \$\begingroup\$ Was that Gnd floating or PE gnd? \$\endgroup\$ Aug 17, 2021 at 13:49
  • \$\begingroup\$ I am not reallu syre of what PE means (i ve done my studies in French). btw it s working , i guess the 100 nF was not sufficient, the 10uF is working fine. \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:51
  • \$\begingroup\$ Do you suggest for me to contnue using the 10uF. as i can see now on the schematic of arduino Uno, theu used a 100nF between gnd and 5V that s why it worked. \$\endgroup\$
    – GellyHamb
    Aug 17, 2021 at 13:52
  • \$\begingroup\$ PE is protective Earth gnd from a 3 pin plug. 10 uF looks like it worked \$\endgroup\$ Aug 17, 2021 at 13:59

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