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Hi,
I'm fairly new to electronics but hopefully this will be a fairly simple question!

I'm going to be building a circuit i've found here:
http://homeeasyhacking.wikia.com/wiki/Nano_Breadboard_Interface

which uses RF modules to communicate with Home Automation stuff...

Anyway, my modules arrived today and i've found a datasheet for the reciever:
http://www.telecontrolli.com/download/schede-tecniche-prodotti/receivers/14-rr3_it.html

Now, according to the circuit picture, the modules connects directly to the Nano +5v pin. I'm sure i've read that the Arduino pins provide 40mA, is that correct?
And if so, the datasheet says this module needs 2.5mA (3mA Max).

There are no resistors in the circuit, so won't this blow up the RF module? Or am I missing something?

I've got an Arduino Uno, which I will be using instead of the Nano. I'm assuming all the voltages and currents will be the same, but is there anything I need to know in terms of differences between the two?

Many thanks in advance!
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I'm sure i've read that the Arduino pins provide 40mA, is that correct?
Yes that is true BUT it only applies to the processor's pins, the ones you control from the software.
The +5V pin is capable of supplying up to 500mA when connected to the USB, and a bit more when connected to an external supply.

You need to power the module, so that means a direct connection with +5V and with the ground to your module.
You will find that the module has a third pin, and that is connected to one of the arduino's processor's pins
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ok...

So if it's capable of supplying 500mA, isn't that worse?
What's stopping it from frying the module that can only handle 3mA?

Sorry if this is a noob question!
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So if it's capable of supplying 500mA, isn't that worse?
Because it is only capable, it won't actually force that amount of current through anything unless the resistance is very low.

See:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
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Ah ok,

so, just so I understand...
how do I tell if a component will limit the current drawn?

i.e. if I connect an LED without a resistor then it will blow? but this RF module won't.
taken from that explanation, the module has a high enough internal resistance whereas an LED doesn't.

but how do I know? I can't see anything on the datasheet about it...
or is it just LED's that have such little resistance?
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if I connect an LED without a resistor then it will blow? but this RF module won't.
Yes.
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the module has a high enough internal resistance whereas an LED doesn't.
Not quite, the module is an electronic device designed to be powered by 5V, so that is what you give it. It will take as much power as you need.

An LED is a component that is driven, in this case it is a non linear component, that is ohm's law does not apply, a plot of current against voltage is not a straight line.

See :- http://www.thebox.myzen.co.uk/Tutorial/LEDs.html

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but how do I know?
Has it got a terminal on it saying 5V ( or at least in the data sheet it says 5V ) - then you know you can detect it directly to 5V.
If it is a component it might have a voltage rating like a motor, or it might have a current rating. If it has a current rating then you arrange the voltage such that the correct current flows. Note a rating is what it can stand, a rating is not the same as saying this is how much it draws.
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