# False triggering on my Arduino Nano

**URL:** <https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704>\
**Category:** General Guidance\
**Created:** [August 11, 2025, 4:33pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704 "2025-08-11T16:33:22Z")\
**Posts on this page:** 6\
**Page:** 3

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**Author:** ![gmcappy53](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/gmcappy53/32/1133213_2.png) [@gmcappy53](https://forum.arduino.cc/u/gmcappy53)\
**Post date:** [August 15, 2025, 1:40pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/41 "2025-08-15T13:40:00Z")

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I just realized I made an error in my drawing, The 9 volts DC input goes to VIN.

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**Author:** ![gmcappy53](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/gmcappy53/32/1133213_2.png) [@gmcappy53](https://forum.arduino.cc/u/gmcappy53)\
**Post date:** [August 15, 2025, 2:08pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/42 "2025-08-15T14:08:23Z")

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just to update you on the changes I’ve made;

1. I am using pin 9 as an output instead of pin 1.
2. I am now powering the relay board with its own power supply.
3. I am now powering the nano with its own power supply.
4. I have gone from external pull up resistors to internal pull up.
5. I have changed my code for my outputs to the relays to read the following
6. 

```arduino
 digitalWrite(5, HIGH);
 pinMode(5, OUTPUT);

```

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**Author:** ![kmin](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kmin/32/1147370_2.png) [@kmin](https://forum.arduino.cc/u/kmin)\
**Post date:** [August 15, 2025, 7:15pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/43 "2025-08-15T19:15:54Z")

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> [@kmin](#):
>
> So none of the relays are driving any load at the moment?

> [@kmin](#):
>
> How long is your switch wiring?

> [@kmin](#):
>
> What is the exact misbehavior?

> [@gmcappy53](#):
>
> I have gone from external pull up resistors to internal pull up.

External strong pullup would be better.

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**Author:** ![Claudio\_FF](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/claudio_ff/32/239118_2.png) [@Claudio\_FF](https://forum.arduino.cc/u/Claudio_FF)\
**Post date:** [August 15, 2025, 7:51pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/44 "2025-08-15T19:51:43Z")

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In an industrial-like environment, it is necessary to apply strong filtering to the inputs. With the following circuit, we have:

- Strong pull-down, 645 Ω
- 14 mA of wetting current for the contact
- 33 kΩ isolation between the input pin and the external world
- RF bypass capacitor and debounce with a time constant \> 3 ms.
- 9 V for the contacts to minimize interference with the 5 V logic section.

 ![98765654543](https://europe1.discourse-cdn.com/arduino/original/4X/7/8/0/7806c42e9dd94bac8d22f19cfd0e712f1606f96a.png)

NOTE: in this case, configure the pin as INPUT, not INPUT\_PULLUP

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**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\
**Post date:** [August 16, 2025, 5:22pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/45 "2025-08-16T17:22:38Z")

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> [@gmcappy53](#):
>
> just to update you on the changes I’ve made;

Have your changes fixed the problem or do you still have interference from the AC?  
What steps have you taken, if any, to help reduce the AC interference?

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**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [February 12, 2026, 5:23pm UTC](https://forum.arduino.cc/t/false-triggering-on-my-arduino-nano/1401704/46 "2026-02-12T17:23:37Z")

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Closed on February 12, 2026, 5:23pm UTC

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