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6601  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 09, 2011, 10:30:48 am
Trouble is I want the DC power supply to be isolated as well.

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Rob
6602  Using Arduino / Project Guidance / Re: Arduino with shift registers to control 70 devices. on: May 09, 2011, 10:23:31 am
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I am currently using 3.3V
Then it looks like it's not OK. I can't remember, is there any reason not to use 5v? Even if there is it would be a quick test to see if that's the problem.

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Rob
 
6603  Development / Suggestions for the Arduino Project / Re: Crystal vs. Resonator (Arduino Uno) on: May 09, 2011, 10:03:22 am
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any issues could be resolved.
Yep, I doubt they'd be the first with a clock signal running around a board.

EME => ElectroMagnetic Emissions.

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Rob
6604  Using Arduino / Networking, Protocols, and Devices / Re: I need a message bus on: May 09, 2011, 09:55:15 am
I'm working on something at the moment but it's not that fast, needs two signal wires, and is only single master. Apart from that it's perfect smiley

100kbps on one wire, offhand I can't think of a PHY layer that will do that except of course Ethernet.

There are 1000s of proprietary protocols around maybe one of them will do this. But I assume you want to DIY or at least get something open source.

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Rob

6605  Development / Suggestions for the Arduino Project / Re: Crystal vs. Resonator (Arduino Uno) on: May 09, 2011, 09:46:52 am
I often wondered why they didn't make use of the free (and more accurate) clock from the 8U but never even bothered to look and see if it was available.

Maybe that big chunky 16MHz signal running half way across the board would be an issue for EME certification.
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Rob
6606  Using Arduino / Networking, Protocols, and Devices / Re: I need a message bus on: May 09, 2011, 09:25:30 am
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(2 wires)
Two signal wires or two wires including earth return?

How fast?

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Rob

6607  Using Arduino / Programming Questions / Re: Software interrupts on: May 09, 2011, 09:16:26 am
You can fudge SWIs by writing to the pins normally used for hardware interrupts, ie INT0-1 and PCI.

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Rob
6608  Using Arduino / Project Guidance / Re: Arduino with shift registers to control 70 devices. on: May 09, 2011, 09:05:17 am
40mA seems like an awful lot, was that mentioned before? I thought we were dealing with a logic signal.

You can probably use a FET or transistor, what exactly does the camera need to trigger? (too many pages to trawl back through) The way it is now I think it gets a 12v logic signal, if the FF is not up to the job the trigger signal will not go all the way to 12v and quite possibly won't propagate to the next FF. Is that what's happening?

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Rob
6609  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 08:43:58 pm
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I read that they would still server their purpose even though they're not connected directly across the coil - is that correct?
It may be, but I've never seen it done like that. I can't see how that will clamp a positive spike.

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Rob
6610  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 08, 2011, 08:27:13 pm
I think you're right, I can't use 12v->12v as such because the input is from batteries that go through the normal charge/discharge range of volts.

But most of those converters have a large input range so that's not a problem.

Thanks everyone, I design by myself with no one to run ideas passed and it often makes things clearer having to spell the problems out.

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Rob
6611  Using Arduino / LEDs and Multiplexing / Re: How many LED's can you run off an Arduino Uno on: May 08, 2011, 08:02:26 pm
The max current per IO pin is 40mA but most people suggest keeping to 20. So that's roughly one LED per pin.

But the 328 has a max total of 200mA for the package.

So I would say as a rule of thumb 10 LEDs max, but 5 would be better (using my 1/2 max rule).

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Rob
6612  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 08, 2011, 11:29:26 am
Yes I should have stated the app.

I have a network with RS485 + power (9-30v) on the wires. I'd like to have a small box to plug my RJ11 connectors in that isolates both the signal (that should be easy) and the power. The theory being that if I need a single node or maybe a few nodes to be isolated I just plug in this box.

As I said before I'm sort of happy to have a reduced V on the output, as long as it's about 9v or more the nodes will be happy, but that does place a limitation on the input as it has to have enough headroom over the 9v. However as the nominal system power will be 12 or 24 volts this wouldn't be a problem.

If I go this route then I can use any DC/DC converter.

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Rob
6613  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 11:16:25 am
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If they weren't at 5V they'd probably get hot
Hence my question, I don't see any mention in the PDF though.

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"You could up the gate resistors (R1-21) buy 10x."
I reckon the gate resistors could be 1k easily and the pull downs 100k. FETs don't need any current to operate. I assume these won't be switched at a high frequency. However apart from using a little more current I don't think it matters.

Flyback diodes usually go across the coil/motor, cathode to +V and anode to the low side or the FET drain.

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I tend to make stupid mistakes
Likewise.
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Rob
6614  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 08, 2011, 10:09:13 am
Thanks Grumpy, I have some idea of the basics but this sort of hardware is a little out of my comfort zone and I was hoping for a black box off the shelf.

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Isolated DC to DC converters do this.
I can't find one that follows the input voltage though, they all seem to have fixed outputs.

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Rob
6615  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 09:57:41 am
I don't know a huge amount about FETs, they are very prone to being zapped though. Personally I'd be worried about running wires from them all over the place, but I may be being a bit paranoid.

Are they logic-level FETs? They are only getting 5v on the gate.

I'm not sure the diodes do anything, they certainly won't snub any motors/solenoids you drive although they might protect against -Ve spikes.

You could up the gate resistors (R1-21) buy 10x.

On the PCB.

What current are you expecting to drive with the FETs? The traces are pretty small. Especially the GND from all the FETs back to CONN3, that could be carrying the current of 10 motors.

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Rob



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