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Author Topic: Driving Relay with Darlington (TIP120)  (Read 5032 times)
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That's what I used! Here, http://www.instructables.com/file/F9LKDFGGU7FXUMH, replace the motor with a relay in your head, that's the best I can do.

That does show a base resistor now doesn't it, but you didn't state using one. Also that shows using a 9 volt source, is that what you are using for your 3 volt relay coil? And why pick a 3 volt relay coil in the first place?
Also that drawing has the diode in the wrong place. Just because something is published on the web doesn't mean it's error free or even correct.

Lefty
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just in case I get wrapped up in this for a while

.... Hell yeah, we understand that, I've been Arduining all day and it's just gone 1900 here.
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Just because something is published on the web doesn't mean it's error free or even correct.

WHAT? Are you sure? DAMN!
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alright guys im back, still having an issue, ill upload the fritzing diagram of how my circuit is connected, maybe this will clear it up


* proto.PNG (44.44 KB, 590x489 - viewed 55 times.)
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alright guys im back, still having an issue, ill upload the fritzing diagram of how my circuit is connected, maybe this will clear it up

Still wrong. I don't see where you are providing any coil voltage for the coil? You have a connection for the output pin to the base resistor, you have a common ground, but where is the voltage to actually power the relay coil on? And are you sure you have correctly identified the emitter, collector, and base leads for your specific transistor. You didn't label them and I'm too lazy to find the datasheet to see if you did identify them correctly, not every transistor has the same lead layout.

And that is not a schematic drawing, just a poor pictorial but I guess better then just english words.  smiley-wink

Lefty
« Last Edit: March 16, 2013, 04:23:51 pm by retrolefty » Logged

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ok, so from what i gathered, hastily mind you, is that an external source was not needed as the rating is only 3v, which the arduino could provide easily. and from the schematics i saw, the source seemed like a bit of a black box that everybody just understood, clearly i didnt. is there a way to do this  without an external power source? also i never claimed it to be a schematic, i used the word diagram appropriately and i think it offers a better view of the physical connections as it's clear im having a problem with the schematic view
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I'm not trying to be funny, but why don't you just connect it like that example I linked to a few hours back. It's dead simple...

From the high voltage side, hook to the relay. The low side of the relay, to the collector. Diode across those two, backwards (cathode stripe to positive input. Emitter to ground.... Arduino digital pin to the base. Arduino earth and transistor emitter earth one and the same.

As Lefty says, you have no high side connection the relay as it shows in your Fritzing...
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Yep if the current's not too big, you can take 5v from the Arduino to the high side of the relay as the relay power source I guess.
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ok, so from what i gathered, hastily mind you, is that an external source was not needed as the rating is only 3v, which the arduino could provide easily. and from the schematics i saw, the source seemed like a bit of a black box that everybody just understood, clearly i didnt. is there a way to do this  without an external power source? also i never claimed it to be a schematic, i used the word diagram appropriately and i think it offers a better view of the physical connections as it's clear im having a problem with the schematic view

Ok the shield 5V pin is a source of 5vdc that could power the relay coil, but only if you are using that Darlington transistor as it drops 2 volts even when fully turned on so 3 volts left over for your 3 volt relay coil (your sure you have the 3 volt relay coil version?). So move the blue wire from the ground pin to the 5V pin and disconnect the emitter lead of the transistor and connect it to a ground pin. That is assuming the middle lead is the collector lead and the right hand lead is the emitter lead and the left lead is indeed the base lead. Why don''t you redraw via those words and see what it looks like after you verify the transistor leads via a datasheet for your specific transistor which I assume is still that npn Darlington one you started off with?

Lefty
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jimbo, that is what i followed but i didnt get it, i think i do now. here's a new diagram. apologies, programmer mentality is a bit different sometimes.


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Here's a really quick and dirty sketch of how it might look....



* IMG-20130316-00154.jpg (307.94 KB, 1600x1200 - viewed 52 times.)
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Here's a really quick and dirty sketch of how it might look....

Too quick, no base resistor shown. Now go to the corner for a time out.  smiley-wink

Lefty
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here's a new diagram.

Yeah that looks right, as long as the transistor pins are correct.... Datasheet shows base, collector, emitter, as you have.

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Too quick, no base resistor shown.

Ooops, well spotted... It's midnight here, time I turned in.

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thanks again guys, still not working but could be a blown transistor, relay, connection etc. atleast now i know where i went wrong. both of you were immensely helpful, thank you again.
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could be a blown transistor, relay, connection etc

Here's how to make a simple tester with an LED indicator. About half way down the page it explains how to check out all the ways through a transistor.

You can check the relay simply enough by putting the tester across the outputs while energising the coil.
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