Having trouble switching a relay for my arduino project

Gabriel Spound wrote:

 

but i'm not sure because it was switching my 10A relay jsut fine.

I can't believe that - your 10A relay must have had additional circuitry on-board such as a transistor.

The information you seek is in the comments on the sparkfun page that you refer to:

(Quote:)

Can you drive this directly from an Aruino?? It says power consumption is 0.9W @ 5.0V, that’s 180mA, which exceeds the current capability of an Arduino port.

Rohar / about 2 years ago /  1

You cannot drive it directly from an Arduino, but you can add a transistor to the circuit. The Arduino activates the transistor, the transistor activates the relay. See the Relay Tutorial to see exactly how this is accomplished.

thank you very helpful, the 10 amp relay is attached to a circuit board so that might be the transistor, i am still new to this kind of stuff, so could you link to me a transistor, i could figure out how to wirte it up, just need to know what transistor to use, thanks

It's in the link at that post (hit Ctrl-F and search for "See the Relay Tutorial to see exactly how this is accomplished.)

It's in the link at that post (hit Ctrl-F and search for "See the Relay Tutorial to see exactly how this is accomplished.)

it just says an npn transistor, there are a lot of those, which one

also they provide a schematic with a bunch of resistors, do i need those as well?

Gabriel,

Please take the time to read it. I quickly scanned it, but it clearly indicated the transistor part number on the schematic, and even provided a URL to the part to help you. How do you expect to learn if you are not prepared to read? The author took a lot of time to write in detail exactly how to go about it.

R2 and D1 are mandatory, the remainder you can ignore.

Please be aware, don't use this circuit to switch mains circuits unless you know what you're doing (i.e. if you are qualified engineer).

If you wish to switch mains, this project is not appropriate for beginners - consider wireless methods.

ok, i've read through it, and i understand it a lot more, but it still doesn't say what transistor i should use

The schematic (where you saw the resistors) has text component identifiers (like R1 and R2) but also specifies values. The value for the transistor Q2 is written right there : )

wait i thought JP2 was the transistor, now i'm confused, how would i wire it up with only the necessary components?

JP2 is not a transistor. You could have looked up 'transistor' in Wikipedia and identified the symbol if there was any confusion.

At this point, I don't know what to suggest I'm afraid.

I'm not prepared to spoon-feed (others might), because then I feel there is no learning.

There are a couple of approaches, perhaps these could help?

1. Look for a tutorial you can understand, if that one is too difficult. Perhaps a youtube video, see here: http://www.mcmajan.com/mcmajanwpr/?p=1259

2. A book on electronics - and study. This one seems to have lots of positive reviews:  http://www.amazon.co.uk/Make-Electronics-Discovery-Charles-Platt/dp/0596153740/ref=sr_1_2?s=books&ie=UTF8&qid=1443829468&sr=1-2&keywords=electronics+for+beginners

i'm not asking for you to spoon-feed me, i'm not asking you to design my project, i've done that, i had it all done i just had trouble with this one thing, and you been helpful, but i'm not just doing this for the sake of doing this, i'm trying to learn, not just trying to get it done, i'm not asking for much more, i just don't know what JP2 is.

JP2 is a connector. What did you think Q2 was? You could have asked yourself; where do you plan to wire your Arduino to this circuit?

And if you didn't know, it was described in the text:

When the ‘RELAY’ pin (aka CTRL) goes high, the NPN transistor connects to ground sending current through the coil (activating the relay) and through the LED (turning the activation LED on).

With that knowledge, it would have been clear that the connection marked 'RELAY' goes to your Arduino, and therefore J2 is likely a connection of some sort.

Strongly suggest you pick up that textbook and study!