Sorry to be a pain. I've tried to get an RGB LED to swith between green & red accorging to the output of a 555 timer. The output is giving high and low as required but all I seem to have done is create a very complicated way of having a green LED lit up (never off).

This is about the only configuration I haven't tried. Before my head explodes from soldering and de-soldering can anyone see if this will or won't work? The problem Ican't get my head around is the common cathode of the RGB and how to deal with it on the NPN & PNP.

Sorry in advance for being idiototically stupid.

 

You can eliminate the NPN transistor and its base resistor. If the timer output isn't high enough to turn off the red LED, add a diode on the emitter.

Before my head explodes from soldering and de-soldering

Get a solderless breadboard so you can test circuits before getting out the soldering iron.

 

You can eliminate the NPN transistor and its base resistor. If the timer output isn't high enough to turn off the red LED, add a diode on the emitter.

Get a solderless breadboard so you can test circuits before getting out the soldering iron.

Won't I fry the 555 if I just go straight from the 555 base to the LED? (I should have added, I intend to have a 2nd load coming out there. Not very high current (20mA or so).

As for the solderless breadboard, I've got loads but spend my time tracking down loose jumpers when something doesnt work.

 

Won't I fry the 555 if I just go straight from the 555 base to the LED? (I should have added, I intend to have a 2nd load coming out there. Not very high current (20mA or so).

You still need the current limiting resistor. If you're using a bipolar timer, it can source 200mA.

As for the solderless breadboard, I've got loads but spend my time tracking down loose jumpers when something doesnt work.

If you're using #22 wire, you need a better breadboard. If you're using thinner wire, you shouldn't go smaller than #24.

Loose wires are an opportunity to improve your troubleshooting skills.

 

Can I just check, is this what you mean? (please excuse the odd layout)

 

Can I just check, is this what you mean?

Yes.

 

Yes.

I'll try it in the morning & let you know. Cheers.
(using my solderless bread board )

 

Yes.

dl324, you're a star. The diode did it (although I sort of like the brown LED that red & green gave without it). I need to look again at it and get to understand the circuit a bit more (ie what's going on with the diode, base and emitter)
Huge thanks. Now I also have to see how well it works with the "other load".

 

The diode did it

Are we talking about the same circuit?

I need to look again at it and get to understand the circuit a bit more (ie what's going on with the diode, base and emitter)

Feel free to ask questions if there's something you don't understand.

 

Here's the diode trick. No transistors needed:

 

Shouldn't need to be pointed out, but the OP is using an RGB LED with a common cathode.

 

Except that the LED as drawn by the TS has a common cathode.

Bob

 

Oops

 

Diode trick for common cathode: