# Relays for dummies

**URL:** https://discourse.nodered.org/t/relays-for-dummies/13714
**Category:** Hardware
**Created:** [26 July 2019 11:11 UTC](https://discourse.nodered.org/t/relays-for-dummies/13714 "2019-07-26T11:11:13Z")
**Posts on this page:** 1
**Showing post:** 53

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### Author: ![Paul-Reed](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/paul-reed/32/66906_2.png) [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [26 August 2019 19:07 UTC](https://discourse.nodered.org/t/relays-for-dummies/13714/53 "2019-08-26T19:07:48Z")

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@iungo - Andrey, [having read your earlier post](https://discourse.nodered.org/t/truck-weight-measurements-with-node-red/14463) and visited [www.ioton.ru](http://www.ioton.ru) I can see that you have experience in hardware development, so thanks for commenting.

I can see in your first post above that you have described a way to test the function of the **MRI-3.3D48** without attaching it to the door controller, by using the Raspberry Pi 3.3V & 5V power lines.

> [@iungo](#):
>
> You do not need 220R resistor.

Is your opinion that the **MRI-24D48** has an internal series resistor or other current limiting circuitry, so that the internal LEDs are not damaged when +24V is applied to A1?

Paul

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