user37878: I'm starting to explore using an Arduino to control a couple of switches programatically. I have read somewhere about relays firing during reboot due to floating inputs/outputs during the reboot phase.
What is the best way to ensure that a relay will not fire on a reboot?
Is there a simple wiring diagram to explain it? I am using an Arduino Uno and a Relay Module.
Any assistance would be greatly appreciated.

user30005: 
What is the best way to ensure that a relay will not fire on a reboot?

put pull-up/down, as appropriate, on those pins.

user359: You can add a pull down/up resistor between the wire and ground/vcc so that when the arduino pin is set to high impedance during reboot the wire is pulled low/high as desired.

user4143: Two things:

If that relay uses a FET input with no pulldown then you should add your own. If it uses an opto-isolator there is no floating problem to deal with.
Don't use pin 13 for a relay - that is connected to the LED which blinks during reset and will "flash" your relay.


37878: <p>I'm starting to explore using an Arduino to control a couple of switches programatically. I have read somewhere about relays firing during reboot due to floating inputs/outputs during the reboot phase.</p>

<p>What is the best way to ensure that a relay will not fire on a reboot?</p>

<p>Is there a simple wiring diagram to explain it? I am using an Arduino Uno and a <a href="https://www.jaycar.com.au/medias/sys_master/images/8978832654366/XC4419-dataSheetMain.pdf" rel="nofollow noreferrer">Relay Module</a>.</p>

<p>Any assistance would be greatly appreciated.</p>
 30005: <blockquote>
  <p>What is the best way to ensure that a relay will not fire on a reboot?</p>
</blockquote>

<p>put pull-up/down, as appropriate, on those pins.</p>
 359: <p>You can add a pull down/up resistor between the wire and ground/vcc so that when the arduino pin is set to high impedance during reboot the wire is pulled low/high as desired.</p>
 4143: <p>Two things:</p>

<ol>
<li>If that relay uses a FET input with no pulldown then you should add your own. If it uses an opto-isolator there is no floating problem to deal with.</li>
<li>Don't use pin 13 for a relay - that is connected to the LED which blinks during reset and will "flash" your relay.</li>
</ol>
