breadboard setup (transistor/relay) not working on arduino ?

I have two almost identical setups 1) a setup build on the breadboard and 2) the final one that's supposed to work along with arduino. The outset is this http://www.glacialwanderer.com/hobbyrobotics/?p=9 ... controlling a highvoltage tool with a relay.

My working setup is not identical to the one linked to. I have no visual scetch, but it's not difficult to visualize: I have a serie between transistor collector and emitter composed of a powersource (12vdc or Vin+gnd), A 100 ohm resistor, a rectifyer diode and the coil of the relay. This part works on both setups .. it's the control-current/voltage on the transistor-base that appears to be the problem. On the working setup, the base is sourced on the same voltage as the collector (12vdc) and added a 1k resistor before connected to the base. It works fine when I breake and reconnect .. the relay clikking away.

I've loaded the blink-scetch example on my arduino and make an analogWrite 255/0 on pin 11 .. along with blinking pin 13. The idea was ofcourse to connect pin 11 to the base. Anyway .. it doesn't work. The arduino is soursed with an external 12v. I've tried to bypass the 1k resistor and also tried using the blinking pin 13, but to no avail. What's wrong?

The transistor is marked "BC 547C" with possible specs at: http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXytvtz.pdf

Any comments?

Perhaps you should find a relay with a 5V 30mA coil so you can drive it directly with an Arduino pin.

hi John Wasser

I reduced the voltage across the transistor to 5v and eliminated both resistors .. and voila, it works ;o)

Carsten