Help reading a schematic diagram

Using Arduino General Electronics
#1

Hey everyone, this seems like (and is) a very nooby question, but everyone needs to start somewhere, right?

Can someone help me on how to build http://www.sparkfun.com/tutorial/Outlet/RelayBoard-Large-v11.pdf this?

All of the individual components make sense to me, however the diagram does not..

Any help is appreciated!

#2

What they're labelling "RAW" is "+V", coil voltage. By the looks of it, that could be as much as 20V, maybe more but not much more. Choose your relay coil voltage accordingly. "Load" is the relay contacts, one terminal goes to the voltage that gets interrupted and the other terminal goes to the device getting switched on/off.

#3

That makes perfect sense, but, what is the middle thing, far left, labeled RELAY, the middle thing (to me) looks like it goes to two resisters and just gets grounded right away?

#4

Q1 is a transistor.

Resistor from BASE to GND is not a requirement... more about good design.

Resistor from BASE to ARDUINO is not optional and is used to limit current to safe value for transistor "turn-on" from 5V Arduino PIN. The transistor is essentially a SWITCH that does "work" when the Arduino ASKS for it. It does "work" that would be unsafe for the ARDUINO pin.

Driving a relay directly can make your PIN (or arduino) never work again. The RELAY is an electro mechanical device that uses magnetism from the coil to move a mechanical switch (close/open "contacts")

Here is my driver circuit.

#5

That picture is awesome, thank you!

If I may ask, what exactly is stopping the flow of current over the relay when the transistor is closed? I guess the concept of the diode in this setting doesn't make sense to me

#6

The diode will have a voltage drop, this and the internal resistance of the coil / wiring will decrease the current till it "stops". The formula is dI = U/L dt.

#7

[quote author=Udo Klein link=topic=102150.msg767099#msg767099 date=1334943607] The diode will have a voltage drop, this and the internal resistance of the coil / wiring will decrease the current till it "stops". The formula is dI = U/L dt. [/quote]

Awesome explanation, thanks guys, I appreciate it; I think I get it now, I'll play with it some more and will find out!

#8