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Topic: Directly Using Relays (Read 575 times) previous topic - next topic

gregr

I've got a couple small relays connected directly to my Arduino. I need more relays with similar specs. Could someone point me to relays similar to this one http://www.radioshack.com/product/index.jsp?productId=2062478 on Digi-Key?

Thanks!

Oracle

Yeah...don't connect an electromechanical relay directly to an Arduino pin.  

retrolefty

Yea, here you go:

http://www.allelectronics.com/make-a-store/item/RLY-515/5V-REED-RELAY/1.html

This one would only require 10ma of current draw from the Arduino I/O pin, about the same or less then a standard LED. It's still a good practice to wire a reversed biased diode across the relay's coil terminals. As long as you stay within max coil current specs and use a protection diode it's perfectly fine to drive a relay directly from a Arduino I/O pin.

Bye the way I couldn't find the coil current requirements of the radio shack relay you listed? You must keep the current draw from a Arduino I/O pn to less then 40ma max and less would be better.

Good luck

Lefty

gregr

Thanks for the link!

Is it safer/better to use a SSR in a situation like this?

retrolefty

You didn't mentioned what you are switching (voltage type, level and current ) with the relay contacts so can't say if one or the other would be better. From the coil Vs SSR input there is no big difference as far as the Arduino is concerned.

Lefty

gregr

I've got a little point and shoot camera with a bunch of the buttons wired to relays so that I can "push" the buttons with the Arduino.

westfw

Quote
From the coil Vs SSR input there is no big difference as far as the Arduino is concerned.

Huh?  Coils have dangerous (to semiconductors) back-emf issues.  SS relays don't.

(On the other hand, many solid state relays are designed to switch AC only.)

retrolefty

#7
Apr 11, 2009, 05:19 am Last Edit: Apr 11, 2009, 05:19 am by retrolefty Reason: 1
Quote
Huh?  Coils have dangerous (to semiconductors) back-emf issues.  SS relays don't.

(On the other hand, many solid state relays are designed to switch AC only.)


With installation of a back EMF diode across the coil and the built in clamping protection diodes in a AVR chip I haven't ever had a problem driving low current relays, have you?

Lefty

transam

#8
Apr 11, 2009, 07:51 am Last Edit: Apr 11, 2009, 07:52 am by transam Reason: 1
You can switch "push the button" with a transistor :)

http://todbot.com/blog/bionicarduino/ <- class 3 page 11 about transistors as switches. Great stuff!

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