Is that 5v or is it 9v (or does it even matter)?
I was planning on using the little power supply thingy that comes with the breadboards.
Well, if we had even the faintest notion as to what you mean, we would probably be able to comment in a meaningful way.
5V, yes it matters. If you have 9V then it has to be regulated down to 5V. You can do this with the onboard regulator but that limits the current for other stuff to about 500mA, so the extra power supply capacity is wasted unless you get another stand alone regulator.
I avoid breadboard like the plague, it is just so unreliable. Make stuff on strip board.
but it's only to be used during the prototyping, then something permanent later
What is "Strip Board?"
It's the one that comes with virtually every arduino kit
Prototyping is exactly when you need a reliable circuit, using bread board leaves you wondering if the circuit design is why it is not working or is it the poor intermittent bread board.https://en.wikipedia.org/wiki/Stripboard
Those are 0.8A regulators quite useless for what you want.You see the "experts" here have never had to have an Arduino Kit, and very few of them use solderless bread board.
So how do I power things?
we always called that perforated bakelite.
Also, can an external supply and the laptop (while coding) be connected at the same time
The relay boards have a separate +5v and gnd connection that is isolated from the actual signal/logic jnputs
So, I get 3A 5V power supply, and plug it into the little jack on the breadboard power supply module, and power the arduino from the breadboardor do I ditch that and plug it directly into the arduino and power everything directly from the arudino? What is "Strip Board?"
Also, there is a pin labelled 5v on the Arduino.. Is this a point for being supplied 5v or to supply 5v to other things.. If the latter, what is the current limit on what can be run from that pin?
Piss all! (To use Mike's terminology. )Yes, to clarify, that is where you feed power into the Arduino, given that you have a regulated power supply at 5 V. You can also use the USB jack (and then take 5 V from the 5V pin) but it connects via a polyfuse rated about 500 mA. In general, use the 5V pin to power the Arduino from your 5 V supply and also connect that supply to everything else in parallel, that requires 5 V.Consider the "Vin" pin and the (2.1 mm pin) "barrel jack" on the Arduino and the breadboard adapter, as of negligible use. Maybe a couple of indicator LEDs.The USB socket on the breadboard adapter is actually more useful for feeding 5 V directly into it, but you need a male-male adapter cable to do it.
The purest would say no but i practice it does not cause any feedback problems that I have come across. In fact they are not isolated despite having an opto isolator on them. You use that extra 5V to insert extra decoupling like the last circuit on this page:- http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
The USB socket on the breadboard adapter is actually more useful for feeding 5 V directly into it, but you need a male-male adapter cable to do it.
I was talking about the relays being isolated.. ie that they do not draw any power from the arduino to operate, only the logic signal, with the operating power being provided via a separate 5v input to the relay boards.
First of all, is noise rejection required across the relay coils,
As a general rule, should I plan to put a 47uf electrolytic across the output of the power adapter where it supplies power to the entire project?
As for as the individual caps, do these go across the 5v (or 3.3v) to ground whenever supplied to a discreet device?
Can the full 3A of the power adapter be fed into the system via this port?
Yes so was I.Yes, mainly a reverse polarity diode to stop back EMF from the coil when it turns off.Yes but bigger if you are drawing more current.
What do you mean by discreet device? It is a yes for active components like integrated circuits. No for real discreet devices which mean transistors and the like.