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What relay to use to switch 12V source using 5V arduino board? Answered

I need to activate
-4 solenoids 12V 250mah each
For as long as 3 hours at a time with a arduino.

I have
-Arduino
-Solenoids
-2A 12V source for solenoids.

I know I need a relay but idk which one I should get. If you could suggest one and send me a link that would be much appreciated.

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steveastroukBest Answer (author)2010-10-22

Just get a ULN2803. Tie pin 9 to ground, pin 10 to 12V supply.
Tie pins 1,2,3 and 4 to your processor pins, tie pins 18,17,16,15 to one end of your relays. Tie all the other ends of your relays to +12V.

Tie the 12V and 5V GROUND lines together.

Steve

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newrev426 (author)steveastrouk2010-10-22

Can this run all 4 solenoids at once? or will it be a 2 on 2 off deal. Im fine with that but was just wondering. The listing I looked at rates it at max 500mah.

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steveastrouk (author)newrev4262010-10-22

That's 500 per channel, so 250 should be fine, and you are only using half the package. You'll have a worst case dissipation of about a watt.

Steve

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newrev426 (author)steveastrouk2010-10-22

Ok last question. There is a lot being sold as ULN2803A, ULN2803xx etc but I want just the ULN2803 right?

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steveastrouk (author)newrev4262010-10-23

Doesn't make a lot of difference. There are minor differences in performance, but you are 50% off the top limits here, so I don't think you'll have issues with any version.

Steve

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newrev426 (author)steveastrouk2010-10-22

I really appreciate it and in my budget too! Im learning about gates in my digital logic class but never know what chips are ones everyone else likes.

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newrev426 (author)steveastrouk2010-10-22

I appreciate it! Will try that out!

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jcamachor (author)2011-05-23


Hi steveatrouk, newrev426,

I have a similar set up, only with 12v fans/ventilators instead of solenoids. Being a newbie to electronics, I was wondering if this is the set-up steveastrouk proposed:


If so, I was wondering also about the output of the 12v source in terms of mA. Does it have to output enough mA to power all 4 solenoids, so 1,000mA (or 1A), and then, does it require some resistor in case only one is on at any particular time or does it have to output just 250mA?

Cheers!

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steveastrouk (author)2010-10-23

Also, put big diodes across the relays, cathode to 12V, anode to the ULn2803. Put the diodes as close to the relays as possible.

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Re-design (author)2010-10-22


This one should work if the arduino can sink 72 ma.

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