Quick relay question

I am trying to get a relay working with the arduino, and I have done this schematic http://www.arduino.cc/playground/uploads/Learning/relays.pdf

So the arduino does switch between 5v and 0v, but my relay needs 9v to trigger. I am trying to use a 9v battery, and the schematic says to use an external power supply, but does not say where to put it.

Can someone tell me where in this schematic would I put the battery to get the relay to work?

That would be relay power V+.

hi l0cke,

to get a relay working properly with arduino you might need to add two components:

  • a transistor to amplify the output - i have a special fond for the little NPN 3904 but others will work

  • and a diode to protect the arduino from inductive current that comes from the coil of the relay- any diode from 1N4001 to 1N4007 may work

and you can also check this schematic (in spanish): http://www.arduino.cc/es/Tutoriales/Rele

bye bye

Both of those are in the schematic he linked.