Make LED not light up until voltage not less than 12V? (Arcade button lights)

[polarwong]

First I would like to thank everyone for helping me out in the last post (looking for a solution to eliminate the thick 20-wire cable). I decided to build a larger cabinet to house everything in one piece.

Now I am facing another problem. The original arcade machine uses 12V incandescent bulbs for lighting up buttons and coin mechs. The original bulbs breaks too often and doesn't look good (the buttons are yellow, the bulbs will make it look more amber than yellow), I ordered some LED lights and swapped them in - and I never expected such problems -

- I cannot turn off the LED lights (they dim a slight bit when I turn them off in the menu)
- Measuring with a multimeter it shows 12V when turned on and around 10V when it should be off.

I understand this is perfectly fine with incandescent bulbs as they doesn't fully light up until the rated voltage is reached, but LED lights have a larger threshold.

Is there anything I can do to make the LED light work? The 12V for the bulbs is output from an IO  board which I cannot modify. I cannot just lower the input voltage as there are other crucial component on the board. There are 5 buttons, each have their 12V+ line and a common ground.

I have very limited knowledge about circuit building and the only thing I know should work is adding a relay but it is not exactly cheap and quite bulky for a little bulb. I still have 20 machines to go and I really want the LED to work.

[MosherIV]

Hi

How about putting a 10V zener diode in line with the LED.

The principle is that the zener diode will not conduct unless the voltage across it is 10V or greater, once it starts to conduct the current flows through it. So putting it above and in series with the LED should make it only turn on when the voltage goes above 11V

[Seekonk]

Do what they do in cars, put a resistor in parallel.  It would be better if you drew out the circuit.  Obviously there is leakage from the driver circuit. I can't imagine how that could happen.  So a 470 (220 if a bleed) ohm resistor from driver to power would eat up a few ma and might make it go out.  They could have been bleeding some current through the lamps to keep them warm and last longer.  Then if that isn't quite close enough, a couple regular diodes.

[Gyro]

Do what they do in cars, put a resistor in parallel.  It would be better if you drew out the circuit.  Obviously there is leakage from the driver circuit. I can't imagine how that could happen.

My guess would be that they are passing enough current to keep the filaments warm when off. It significantly reduces thermal shock in flashing applications, increasing lamp life. Yes a parallel resistor should do it (the resistor/diode combination would help reduce heat dissipation).

If you study the circuit you might find a 'keep-warm' resistor in parallel with the driver that you can simply snip.

[Totalsolutions]

Just stick with decent quality lamps not chinese fakes and you will be fine. Much easier and more authentic. Lamps will flash, dim and fade as required where LED's are on or off.

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[oPossum]