I asked how can I turn on a 12V relay from a ttl signal before and I got the circuit below as a response. I tested it and it works fine but unfortunately I tested it by supplying 12V into the 2.2k resistor. Now when I've connected it to my little cpu it doesn't work. When I switch on the appropriate pin it can only muster .67 of a volt. The pin has an internal pullup and does switch from 0 to 5V without the transistor connected. Did I get the wrong transisitor or something? It's a BC338 from jaycar. I dunno what these figures mean but in the catalog it says "Diss @25C 500mW, Vcb 30V, Ic 800mA Hfe 100, Hfe Bias 100mA"
Many thanks yet again Michael
o----o----- +12V | | --- --- ^ | | 1N4001 / \ | | Relay coil --- --- | | -----o | / IN |/
----\/\/\/-----| 2K2 |\ Misc. NPN -V| | | --o-- GND