Help with choosing a transistor

[Messugga]

Hey guys

Now, I used to know how to do this, but I'm kinda rusty.
I've been tasked to build a circuit to switch LEDs on and off, by making use of transistors. Now, the problem comes in with choosing which transistor to use. I have a maximum of 15mA to actually switch the transistor with, but I'd like to keep it <10mA.
Can anyone help me out with a circuit maybe or at least tell me which transistor I should be looking at?

Cheers

 

[zophas]

Any general purpose small signal transistor should do the trick. E.g BC109, BC547
There are lots of circuits on the net to flash leds. Look for multivibrator/oscillator circuits. You could can even get a led that flashes on it's own, no circuit required. Also try Yebo Electronics for kits.

 

[.Froot.]

Flashing LEDs is an option, although you could try using a 555 timer to give the LED a pulse. It's a very easy method of flashing LEDs...

 

[zophas]

Yes, IC's would make many things easier. But I think the OP was specifically asking about using transistors to do the flashing. That's why I did not mention IC's. Maybe he is doing a "back to basics" course?

 

[.Froot.]

Could be. I'm not always fond of transistors because they have a tendency to um.... crash out on me, but will take a lookie for you.

 

[.Froot.]

http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#flash2.gif
It's the one with the two transistors and the capacitor. "Two Transistor LED Flasher"

 

[Messugga]

well, thing is, the LEDs need to be controlled by a microcontroller, so just flashing them's not really quite what I want to do. Thanks for the suggestions though, much appreciated!

 

[zophas]

I built a timer circuit with a PIC microcontroller and some 7-segment displays and I used BC547's to drive the displays. Worked like a charm. Most of the transistors I had in my junk box from things that I cannibalised.