i need a circuit with 2 switches, so when you press switch A, LED A comes on and LED B goes off, then when you press switch B, LED B comes on and LED A goes off. whats the easiest way to make this?

 

Probably a simple bistable multivibrator, two transistors, four resistors, two LED's, and your two switches of course.

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Some similar...

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thanx. much appreciated

 

1 problem: i need a LED to stay on until the other button is pressed, switching to the other LED (which is then to stay on).

it is to be used to change between two different modes , so when i press button A, i need circuit A to come on and circuit B to go of, and vice versa

any ideas?

 

That's what bistables do, the one with the chip is actually identical to my suggestion using two transistors - both will light only one LED, when you press the other button it's LED will come on and the other LED will go off.

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do you have any schematics?

 

Here's a quick bistable I've just drawn, you can fit the switches in a number of ways:

1) From the base of the transistor to the emitter, in which case pressing the key down turns that transistor off, and lights the opposite LED.

2) From the collector to the emitter, where pressing the key down turns the other transistor off, and lights it's own LED.

The main difference is what happens if you press both switches together, with option 1 both will go out, with option 2 both will light.

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Bistable_862.gif (2.7 KB, 526 views)

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are the transistors just general transistors?

 

Yes, general purpose NPN transistors - nothing special at all, I'd normally use BC107's - but I use them for everything 8)

You could even use germanium transistors if you wanted!.

It's a very simple circuit to understand - all you need to know is that if you take the base of a transistor high, it's collector will be low. And if you take the base low, the collector will be high. Work from that, and follow the operation of the circuit!.

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i cant get it to work. when i press button A, LED A comes on, press button B, LED B comes on, press both, both LED's come on. av tried it connected all different ways. what am i doing wrong?

 

Very sorry! - I've had a momentary loss of brain! - I drew a circuit half way between an astable and a bistable, try this one instead.

Luckily no body noticed :lol:

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Bistable_134.gif (2.3 KB, 501 views)

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i have re-designed my circuit, so rather than have 2 buttons, i now have 1 which switches between mode A and B by pressing the same button... made this by usin an alternating on/off switch and making use of the extra gate to light the second LED. note that this is the unedited circuit.. if anyone wants an edited version post here and i will make it