Help with a simple circuit

[GaryP]

HI, I am a complete noob with electronics but I am trying to work with an Arduino and a GSM phone module. My problem is that the designer of the module neglected to put in a software way of turning the module on (you have to press a switch on the module-Yikes).

I found a circuit in the design manual for the module (PDF page attached) that shows how to implement a power-on circuit using a NPN transistor and a couple of resistors. I figure I could solder onto the PWRKEY side of the switch and breadboard the circuit.

My questions/problems are these (I don't want to fry anything)
1. The supply voltage on the GSM module (provided by the Arduino) is 3.3V, they have the same ground. The digital output pins from the Arduino are 0 or +5. If I use a digital output pin to drive the transistor (the base, I think) will I fry anything?

2. The transistor in the diagram is a surface mount one that I can't imagine getting on a breadboard. What could I use instead?

Thanks for any help.

Gary

[pebe]

Hi Gary,
The transistor, Q1, is used as a switch, so when you apply current through the 4K7 resistor to its base, it 'switches on'. In effect, its collector is connected to its emitter, like a switch. You can safely apply 5V to the resistor without causing damage to the 3V circuitry of the rest of the module.

The BC847 is a small signal NPN transistor, and you can replace it with something like a 2N3704 or a BC547.

[GaryP]

That's great. Thanks for the help!

I was worried that the 5v would somehow infiltrate the 3.3v circuit (not understanding exactly how transistors work).

[GaryP]

Breadboarded it and it worked great! Thanks for the help.