Automotive Relay question... for future reference.

Forum 2005-2010 (read only) Hardware Interfacing
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Hello,

I haven't yet bought an Arduino, but I intend on doing so very soon. Before I do though, I would like to find some information regarding the Arduino and relays, specifically automotive relays.

First off, you should know that I have very little to no experience with electrical hardware. I've setup and installed automotive wiring, computers, and tinkered with odds and ends every now and then, but I've never worked with the actual hardware parts like diodes, etc.

My aim is to use an Arduino to switch control circuits to various components within my vehicle. For example, switching on and off a interior light or something similar.

I don't want to 'blow things up' or wreck an Arduino, so any guidance would be great.

I've done some reading and so far I think I'll be needing a diode to block current from going the wrong way, into the Arduino (if I understand diodes correctly).

So here's my questions summed up, and in a more specific manner:

  1. What hardware would be needed to enable an Arduino to control an automotive relay (I assume the relay would be 12v)?

  2. I 'think' the Arduino has a 5v output; could that output be used for the 'switching' 12v current?

Again, I know very little about this hardware stuff. I figure there has to be some people on here who know their stuff. Why not ask?

Anyways, any guidance or response will be greatly appreciated. If there's any questions or things that aren't clear, feel free to ask me.

In the meantime, Happy New Year!

Thanks! :slight_smile:

PS: Sorry if it's unclear, I wrote this post at 4:30AM or so...

2
  1. What hardware would be needed to enable an Arduino to control an automotive relay (I assume the relay would be 12v)?

Depends on what relay you use. Some have low current 5 v coils and therefore nothing is needed.( except a diode for feedback protection) Some use higher power coils and you will need a transistor or better yet a photo transistor to isolate the Arduino from the relay circuit.

  1. I 'think' the Arduino has a 5v output; could that output be used for the 'switching' 12v current?

Yes of course it can with the proper circuitry.

My advice to you, is to start going to the free resources on the net to learn about basic electronics. I bought the Basics of electronics or electricity or something by Forrest Mimms from Radio Shack years ago, when I started working on cars. It is an amazing book, because it brings electronics down to my level. ( which is very low) Not to mention his art work is amusing.

If you can't find the Forrest Mimms Book for beginners, there are also a huge selection of web sites with walk through like tutorials on how to use diodes, transistors and even old 4000 series CMOS and TTL chips that are cheap and widely available.

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Hello,

Thanks for the replies.

I have done some thinking regarding my initial setup plan...

From reading a few pages, and watching a few videos, it seems that a transistor can be used as a switch. I think that would rule out the need for a relay in my case, because if I can achieve a switch with the transistor, why add a relay?

I think a bonus to using only a transistor would be eliminating the mechanical aspect of the relay, possibly making the whole thing more responsive.

So couldn't I just use a transistor?

I'm not sure on the voltages though. Would it work with 12v on the collector and 5v on the base?

If someone could explain to me the relation between the base and the emitter, I'd be grateful. From what I've gathered so far, the emitter's final voltage depends on that which is supplied to the base. I assume I would still need a resistor between the Arduino and the base.

5v from the Arduino to the base with a resistor in between, and then the 12v circuit from the vehicle would be run through the collector and emitter.

Let me know what you think, and if I'm missing something...

Also, I was half way through making a diagram for what I'm trying to explain, in the process I looked for examples of what the circuit symbols mean. I came across this


The top image is what I'm aiming for, but I'm curious as to why there's a diode in the second image... could someone tell me the difference? :slight_smile:

Thanks again!

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Oh, ok. Sorry, I must have overlooked the line regarding the Snubbing diode. I read your post when I was half asleep. Thanks for explaining that.

Edit: Anyways, I think I have a decent idea of where to start. My next step would be to get an Adruino and try some things out.