Show Posts
Pages: 1 ... 436 437 [438] 439 440 ... 582
6556  Using Arduino / Networking, Protocols, and Devices / Re: I need a message bus on: May 09, 2011, 09:25:30 am
Quote
(2 wires)
Two signal wires or two wires including earth return?

How fast?

______
Rob

6557  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.

______
Rob
6558  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?

______
Rob
6559  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 08:43:58 pm
Quote
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.

______
Rob
6560  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.

_______
Rob
6561  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).

______
Rob
6562  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.

______
Rob
6563  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 11:16:25 am
Quote
If they weren't at 5V they'd probably get hot
Hence my question, I don't see any mention in the PDF though.

Quote
"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.

Quote
I tend to make stupid mistakes
Likewise.
______
Rob
6564  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.

Quote
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.

______
Rob
6565  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.

______
Rob



6566  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 07:33:35 am
The LDR won't work, it's just connected to VCC with no divider. You could connect it to GND and use the internal pull up resistor (dodgy) or add an external resistor and tap from the centre of the two.

______
Rob
 
6567  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 08, 2011, 07:24:49 am
I guess it pretty much has to be a transformer, it's just that I don't want to do it, I'd like a little black box filled with clever stuff by someone who knows about this type of electronics smiley

I may decide that the far side has to have it's own PSU/battery, that's certainly an option but I didn't want to force that as it might be a remote sensor(s).

I can also stipulate that one side will be for example 12v, and the source > 12v (or whatever headroom is required). In this case there are a 1000 options.
 
_____
Rob
6568  Using Arduino / Project Guidance / Re: Doghouse automation design advice on: May 08, 2011, 06:58:00 am
How about PDF, I don't seem to have anything to read PS.

______
Rob
6569  Using Arduino / General Electronics / Isolated N to N volts on: May 08, 2011, 06:29:54 am
Can anyone tell me what you call a "DC/DC converter" that will take any DC voltage (well say 9-30v) on the input and produce the same voltage (a small loss is OK) on the output that is isolated from the input?

Please don't say a transformer smiley, I don't want to dick around changing from DC/AC/DC. 

I though a quick Google search would find something, and there are no end of DC/DC converters but they all have fixed OPs as far as I can see.

I'd like a PCB mount device, good for around 1-2A.

Maybe it can't be done because you have no reference across the isolation barrier, although a VCO could do that and I'm sure the Murata (or whoever) guys would be up to the job.

EDIT: Actually thinking about it 2A at 30V might be a bit of an ask. Still any ideas welcome.
______
Rob

6570  Using Arduino / Programming Questions / Re: Multiple Timer SYNC problem on Mega board on: May 08, 2011, 06:14:09 am
From the data sheet

Quote
Modifying the counter (TCNTn) while the counter is running introduces a risk of missing a compare
match between TCNTn and one of the OCRnx Registers.

Maybe you should stop the counters, do the updates, then restart. Then there's this

Quote
Writing to the TCNTn Register blocks (removes) the compare match on the following timer clock
for all compare units.
I'm actually not sure what that means exactly  smiley-confuse, maybe do the TCNT write before the OCRn writes (although you said that they seem good after the first run)

______
Rob



Pages: 1 ... 436 437 [438] 439 440 ... 582