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Old 06-10-2012, 10:38 AM   #11
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That was one of my questions, and I think you havve a good point. Come to think of it, my old laptop wasn't incredibly reliable, and the wireless shield is cheap. Am I on the right track with those relays I posted?
That should work just fine. You can also use solid state relays (SSR), which can be driven directly by the arduino.
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Old 06-10-2012, 10:52 AM   #12
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Hi

Ok, since this is gaining a life of it's own.

The original post included a question "can I use an old laptop in place of a wireless shield?" or something very close to that. My comment was in reply to that question. If you believe that replacing a wireless shield with an entire laptop is a good idea, go for it. I'd go for the shield.

Bob
Never said it was a good idea, it's just another option. I tend to re-use and re-purpose as much as possible. I've resurrected older computers for people that wouldn't otherwise have been able to afford a new one (up until recently I had an old 486 system running as a file server). If he wanted to, he could use the laptop instead of the arduino and wireless shield and relay shield, so now it's one box instead of three.

I'm just providing other options.
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Old 06-10-2012, 01:22 PM   #13
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Quote:
Originally Posted by Eighty2Fifty1 View Post
That was one of my questions, and I think you havve a good point. Come to think of it, my old laptop wasn't incredibly reliable, and the wireless shield is cheap. Am I on the right track with those relays I posted?
Hi

The relays look fine for anything up to a hot water tank heater. With mechanical relays, be sure you have enough power supply current available to run them. They likely will pull more current than all the rest of the stuff in your system. Still not a lot of current, but it could nuke a tiny wall wart.

Bob
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Old 06-10-2012, 02:41 PM   #14
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I used matchport for my wireless interface

http://www.lantronix.com/device-netw...matchport.html

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Old 06-10-2012, 06:21 PM   #15
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Hi

The relays look fine for anything up to a hot water tank heater. With mechanical relays, be sure you have enough power supply current available to run them. They likely will pull more current than all the rest of the stuff in your system. Still not a lot of current, but it could nuke a tiny wall wart.

Bob
I'll have to sit down and draw the schematic out, but I'm thinking my 110VAC power in will split off and go two places. One, to the wall wart power supply for the Arduino (7-12VDC); and two, to the input side of the relays (110VAC). It says that the relay brick needs +5VDC to power the coils, but I think it gets that power from the Arduino as well. The Arduino output sends a signal to a transistor that in turn energizes the relay coil.

Would I gain anything by using SSR's? Probably depends on the duty cycle of the lamps, but I doubt they would be turning on and off so rapidly to burn out a relay. In any case, I'd probably fry the lightbulb first.
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Old 06-10-2012, 10:33 PM   #16
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Quote:
Originally Posted by Eighty2Fifty1 View Post
I'll have to sit down and draw the schematic out, but I'm thinking my 110VAC power in will split off and go two places. One, to the wall wart power supply for the Arduino (7-12VDC); and two, to the input side of the relays (110VAC). It says that the relay brick needs +5VDC to power the coils, but I think it gets that power from the Arduino as well. The Arduino output sends a signal to a transistor that in turn energizes the relay coil.

Would I gain anything by using SSR's? Probably depends on the duty cycle of the lamps, but I doubt they would be turning on and off so rapidly to burn out a relay. In any case, I'd probably fry the lightbulb first.
Hi

The relays are likely rated for several million cycles. Unless you get really nutty with a PID you will never burn out a relay. The main advantage of SSR's is that they don't pull as much off of the 5V power supply. I haven't looked up the relays on the board but I would not be surprised if they each pulled 100 ma off of +5V.

Bob
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Old 06-11-2012, 05:24 PM   #17
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They pull about 70 mA each. I'll probably get the shield wwith 2 relays, I'd only need one for a heat circuit and one for a cooling circuit. From what I've been reading, the relay coils get their power from the +5VDC regulated output pin on the Arduino board. I believe that pin is rated for 200 mA. So now my concern is to make sure the power supply that powers the Uno and then the board can handle the draw?

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Old 06-11-2012, 10:22 PM   #18
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Originally Posted by Eighty2Fifty1 View Post
They pull about 70 mA each. I'll probably get the shield wwith 2 relays, I'd only need one for a heat circuit and one for a cooling circuit. From what I've been reading, the relay coils get their power from the +5VDC regulated output pin on the Arduino board. I believe that pin is rated for 200 mA. So now my concern is to make sure the power supply that powers the Uno and then the board can handle the draw?
Hi

The four relay board you started out seems very fairly priced at $11. I'd go for it. You never know when you might decide to switch another load. Fans, alarms, lights, pumps, valves .. who knows. There's always more stuff out there to fiddle with.

Yes, you are correct about the power supply. Since the whole thing runs off of +5, you need a supply that will handle the relays plus the Uno plus what ever else you are tacking on (wireless card, display etc). If you are going to buy a power supply, one in the 3A to 5A range should be dirt cheap (sub $10). My only worry is that you are trying to re-purpose a cell phone supply that might be in the 500 ma range.

Bob
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Old 06-12-2012, 05:06 AM   #19
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I'll keep that in mind. I found a whole slew of the things on Mouser's website, but I'm sure I have one sitting in a drawer somewhere.

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Old 06-12-2012, 10:07 AM   #20
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Any recommendations for a 5v power supply for this kind of setup

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