Relay card for GPIO


13 posts
by ok1cdj » Wed Jun 27, 2012 8:27 am
Hello, you can get board with 8 relays (250V/10A). Size is 50x100mm.

Kit:

http://www.hamshop.cz/avr-a-arduino-c16 ... uino-i178/

Or ready board

http://www.hamshop.cz/avr-a-arduino-c16 ... uino-i179/

Regards, Ondra
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by pjc123 » Sat Jul 07, 2012 9:25 pm
I just ordered this board:

http://www.sainsmart.com/relay/8-channe ... logic.html

Just what I was looking for; 8 channels, optoisolated inputs and 10 amp high current relay outputs. With a jumper on the board removed, the optos accept a 3.3V input while the coil of the relay is driven by the 5V line. I plan on running 12V at a couple of amps through the relays.

I found a couple of schematics and detailed specs for this device, but unfortunately this forum does not allow the upload of pdf files.
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by pjc123 » Tue Jul 10, 2012 5:59 pm
I received my sainsmart board today and it works great except their isn't enough juice on the 3.3v rail to drive the optos bright enough to allow enough current flow through the transistor on the board that drives the coil, even when connecting directly to the 3.3V pin; the optos are on the hairy edge with the relay working occasionally. It would have been nice, but I fixed it by using the GPIO output to drive a transistor to supply 5V to both the opto and the coil and it works great. Between the transistor and the 2.2k resistor going to the GPIO output there is enough protection for the GPIO line, and of course the contacts of the relay are completely isolated.
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by bobc » Tue Jul 10, 2012 6:32 pm
I wish someone would sell a relay board inside a box with IEC outlet all wired up safely to CE standard.

I don't mind dabbling with electronics I don't really understand, but dabbling with power electronics is something I have never been comfortable with since that accident with the mains transformer...
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by felixfurtak » Mon Aug 13, 2012 10:02 pm
I've seen a couple of projects that get round the electrical safety issue by using remote control mains power sockets. These can be bought cheaply from pretty much anywhere and are usually already CE approved, etc. The Pi GPIOs can then be interfaced with the remote control which can control the relays inside the power sockets without having to dismantle them or risk high voltage shock. It's a neat way of avoiding the safety issue that you mentioned.. If you search around you'll find plenty of information on how to do this.
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by Saulverde » Fri Aug 17, 2012 12:20 am
Does anyone have any thoughts on something like this?

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=328
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by Saulverde » Fri Aug 17, 2012 2:12 pm
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by jfornango » Tue Oct 02, 2012 4:54 pm
I would assume that the first thing you want to do is put any of these in a case with panel-mounted connectors to the powered side of things.


Still, these are all sweet. I've seen plenty of projects that try to directly power 5V devices from the GPIO. The first recommendation I always give is to put a relay set in between, to that you can use the 3.3V to drive the relay, then feed whatever voltage/current is needed through to the circuit.
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by techpaul » Tue Oct 02, 2012 7:27 pm
A relay is an expensive, large and power hungry way to change between 3V and 5V. There are many articles in these forums on translating between 3V and 5V levels even bidirectionally.
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by Saulverde » Tue Oct 02, 2012 7:47 pm
techpaul wrote:A relay is an expensive, large and power hungry way to change between 3V and 5V. There are many articles in these forums on translating between 3V and 5V levels even bidirectionally.


But you didn't give names, acronyms or links for any of them so I have no more information having read your post than I did before. I just vaguely have the impression that I could do something more efficiently, which I typically feel anyways.
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by techpaul » Tue Oct 02, 2012 7:59 pm
Look at link in my sig, look at the Wiki for Pi, do a google search for FET level translater. Even look at the often quoted on these forums Sparkfun 2 or 8 channel level translater.

Stop posturing and do some simple searches.

As an example it is possible to get in one off quantities 8 chnanel BI-directional level translaters ICs for less han 2 pounds, more often than not a single direction relay will cost the same possibly even get two, but use many orders of magnituide more cuirrent.

Relays need proper driviung and protection.
Last edited by techpaul on Tue Oct 02, 2012 8:09 pm, edited 1 time in total.
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by techpaul » Tue Oct 02, 2012 8:01 pm
Also look at this thread
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by Saulverde » Tue Oct 02, 2012 11:25 pm
That's all I was saying. Not everyone would know to search for 'FET'. If you had said what you did and then said a FET would work better then it would have led me down the rabbit hole of internet searching and I could have probably run across most of what you were talking about. Thanks for adding the info.
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