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LED Help (no0b) Answered

I am just getting into building my own electronics/gadgets. I have decided that my first project is going to be a simple (hopefully) led light that can be toggled on/off via a small push button and most importantly can be toggled on/off when in contact with a metal rod. So, when the led is in contact with the rod, it will turn off, and when not, it will light up. The power source for the led will be a cr2032 (3 volt) battery. For a visual, think of those small led lights that you can add to your key chain. It pretty much the same concept, but if the led was on, and you were to place it on something metal, it would turn off. I think I can bring my project up to the point of a working led with a push button, but have no idea on how to set it up to turn off when in contact with metal. Any help would be greatly appreciated. Thanks Dan

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dyidan

9 years ago

Thanks for the help. I am going to spend a few days (maybe weeks, if it doesn't stop snowing) experimenting the techniques mentioned below. Thanks for the digram 11010010110! Also, Does anyone here have the tools and time to build a custom printed circuit board? I will be able to (and would like to) pay.

try a circuit like this start with the values of resistors shown and play with it you need the max resistance resistors (specially the 100 K one) with which the led lights with sufficient brightess this circuit does take power from the battery when metal strip is there but much less than short circuit a more power saving circuit can be built with FETs but i dont know how to connect them transistors like C945 C547 and some others should be ok. entry assignment (which entry is what) is not the same in all transistors

3v.png

or if you live in the US you could just use some 2n3904 I always had trouble with darlingtons for some reason, they just never worked... neither did joule thiefs...

you can use one transistor only (pick one with really high amplification)

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dyidan

9 years ago

Battery life is crucial, so a short-circuit technique may not be a sufficient solution. Let me try to explain myself a lil’ better with a process outline and diagram. - The pushbutton will be the main ON/OFF switch. When the LED is turned ON (illuminated) via the pushbutton, the LED will interact with the metal rod. And when the LED is turned OFF via the push button, the LED will remain off regardless if it’s touching metal or not. So the process would be: - Turn ON LED via pushbutton. - Metal strip located on the circuit board touches something metal and turns OFF the LED (no power being drawn from the CR2032). - Separate the metal strip and metal rod, and the LED turns ON (illuminates). - Turn OFF the LED via the pushbutton and the LED will remain off regardless if the metal strip on the board is touching anything.

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dyidan

9 years ago

Thanks for replying Kiteman.... The light will be off more than on... the light would only be on for a brief moment.

In that case, go with the short-circuit. The light will blink out when you touch metal (or any other conductor).

short circuit wastes energy. itll kill a cr2032 in very short time if you use resistor with the led then short the led only and leave the resistor outside the affected part of the circuit. this will let the battery live a bit longer but not much

You mean you don't want to go with the shortcircuit, LOL

No, he wants to have the LED on when he holds the button, and go off when he touches metal. For a simple circuit, with a brief contact time, the short circuit is the easiest to make.

The simplest way is to set up a short-circuit - connect your circuit up as a simple LED torch or throwie, but with the legs of the LED sticking out as your probe.

When they both touch the same piece of metal, the LED will be shorted out (the current will flow through the metal, not the LED), and the LED will go out.

Only useful for brief contact, though, as a short like this can cause batteries to heat up.

It would be better, and make more sense, to set up the LED to come on when you touch metal.