I want to use the arduino as a switch for 3,5v circuits. So I have multiple times, 2 wires that need to be "open" or "closed" like a switch and I want the Arduino to do the switching.
How to do that? With relays? Is there some IC with multiple relays in it?
Relays are the most straightforward way to go.
A relay may have more than one set of switch contacts. They would activate together, working off the same relay coil. There may be relay packs with multiple coils and contacts.
What is the application ? Relay is OK, if you need isolation, control higher voltage / currents , motors. But they are "slow", reed relay are a bit more faster, but lower rated applications. For motors controls, relays are just fine, if that is your application - example : Robot.
FETs may be good as well. Tell us what you are switching and how fast.
I'll be switching the contacts of an MP3 player.
The thing is I can't just put a HIGH on the connections because the MP3 player's buttons aren't working that way.
So I'll have to "simulate" a finger push on the mp3 player's button, by shorting the 2 connections beneath the button. (by closing a relay, or like "closing" a switch)
it doesn't have to be extremely fast, just the same like bushing a button
In that case, unless you know for sure what voltages/polarities/etc are across the switches the easiest way is to use relays. You can get very small ones that can be controlled directly from an Arduino pin.
I do know for sure it only runs 3,5V max through the relays. Would a FET work too? If it would which one? It has make the throughput "zero" or "max"
Cool, because I've got about 10 P2N2222A laying around.
this should be it's data sheet: http://www.onsemi.com/pub_link/Collateral/P2N2222A-D.PDF
so this would make it possible to switch the MP3 player's buttons with an Arduino and some P2N2222A Transistors.
Or would I need other Transistors?
I will go for a relay. A reed relay. The use of a transistor “may work”, but that thing is, I don’t know how the push button of your MP3 player is connected. If the push button is connected like : – switch – gnd than you can use a simple transistor. The switch connection is replaced by Collector and Emitter ← at gnd. Place a limiting base resistor of 1 K to 4.7 K , you wil be fine, and that might work.
Ok, thanks. I'll just try it out.