use a pushbutton to control a light

audioguru said:

There are 21 LEDs. There is nothing to limit the current and we don't know if some of the LEDs are in series.
If the LEDs are all in parallel and use 20mA each then you need a darlington transistor that can switch 0.42A from a low current from the CD4027, not a little BC548 transistor.

Click to expand...

what you're saying is it's better to use a different transistor? it's more reliable? if it doesn't affect i could buy it instead of bc548..


well, i was about to choose the resistor but i don't know if i should buy 1/2w 220k, 1/4w 220k, 1w 220k, 2w 220k or SMD 220k??.. what should i buy?

and for the 1k resistor, here has N.T.C. 1k, is this the one i should buy??

transistors they have BC548B and BC548C, i don't know what's the best to buy or what's the difference.. the price is the same..

sorry but i'm so noob.

1/4W carbon or metal film is fine for all the resistors used in the circuit and you don't want SMT, get through hole.

You really need to know how much current the light draws and should measure it with a multimeter.

Get the BC548, it has a higher gain which is better.