Is it possible to replace keyboard LEDs with neon indicators and a single inverter?

[seanspotatobusiness]

I want to modify my keyboard for a retro cyberpunk look and replace my LED (scroll, caps and num lock) indicators with neon indicators. I can power a neon lamp from a low voltage using a laptop CCFL inverter but I was wondering if there's any way I could power three from one inverter. They cannot be connected in parallel because only the one with the lowest forward voltage (or whatever the correct terminology is) will light. They must be connected in series. Is there some way I could use transistors to move the neon lamps in and out of the circuit? When all lamps are off, the inverter would produce a potential of, like, a 1000 or more volts.

 

[Alec_t]

It no doubt could be done, but it may not be simple. You'd have to take great care that the 1kV didn't somehow get to the keyboard electronics. Opto-isolators could help there.

 

[kellys_eye]

They can be connected in parallel - use a series resistor with each (in the MΩ range) to balance the voltage/current draw.

 

[Alec_t]

You could put a permanent load across the inverter to keep the volts down.
What are the strike voltage and current draw of these retro neons?

 

[Audioguru]

An NE-2 neon bulb operates from 60V to 90V through a current-limiting resistor of about 100k ohms. Then it is a string. Many strings can be connected in parallel. Simply use a 100k resistor in series with each neon bulb and use a 120V inverter.

 

[hevans1944]

I want to modify my keyboard for a retro cyberpunk look and replace my LED (scroll, caps and num lock) indicators with neon indicators.

This can certainly be done, but just because it is possible doesn't mean it's practical. I see two problems: size and voltage requirements. The most common neon lamp suitable for use as a keyboard key-status illuminator is the ubiquitous NE-2, mentioned by @Audioguru in post #5. Suggest you obtain a few of these and see if their size is going to be a problem.

The voltage needed to "fire" an NE2 is around 90 V DC, dropping to about 65 V, needed to sustain the glow discharge, after the lamp is lit. See this datasheet. You don't need (or want) thousands of volts for this. One hundred volts or so and a current limiting resistor, in series with each lamp, is all you need. All the lamps can be powered in parallel from the same power supply because the current-limiting resistors provide isolation of the lamps from the power supply rails.

The problem I see is how to turn the lamps on and off by placing a solid-state switch (transistor) in series with each lamp, supposedly controlled by a low-voltage logic-level signal, i.e., the original LED power source. So now you are mixing relatively high voltage with low-level logic voltages on your keyboard, which is presumably connected to a microprocessor that sorts out individual key presses.

Make just one mistake and you will have ruined the keyboard, probably beyond any hope of a cost-effective repair. So, are you really willing to risk that for a (possibly) kwel retro-looking or steam-punk or cyberpunk keyboard? Jeez... maybe you could just purchase a prop from the now-defunct Warehouse 13 television series. Oh, wait, props for TV shows don't have to actually work... nevermind.

 

[kellys_eye]

A circuit to flicker the existing LEDs at 50/60Hz would probably be safer. Putting the flickering LEDs behind some extra thin perspex would give the 'crappy' look neon's are noted for too....

 

[metalcore]

Can only be connected in parallel using a resistor.

 

[seanspotatobusiness]

Thanks for everyone's responses. The keyboard is not valuable so I don't mind risking its destruction for my project. I want to drill holes in the keyboard for the lamps to protrude out of the case.

I have designed this circuit which reroutes the output of the inverter to a resistor when the lamps are not lit to prevent the inverter producing a very high voltage when the lamps are not lit. I actually have two circuit designs but I don't know whether one is better than the other, other than the first using fewer components.

What kind of transistor should I use? The CE voltage will be high but the current will be very low (less than 3 mA for the transistor attached to the 62K resistor).

 

[Alec_t]

Ummm. All your switching is set up for DC, but the transformer/inverter output is AC .
If a transistor collector junction breaks down under high voltage stress, the keyboard electronics (and possibly the PC to which the keyboard is attached) is at severe risk of being fried. Consider using opto-isolators.

 

[seanspotatobusiness]

Are there opto-isolators which work with AC? If there are, would it be cheaper anyway to combine DC opto-isolators with a triac?

Here's opto-coupling triacs.

 

[Alec_t]

Yup. For example, here's some 800V-rated optos with triac outputs.

 

[seanspotatobusiness]

Version 2 has triacs and opto-couplers! Edit: MOC3010 should maybe be MOC3083.

 

[Alec_t]

I've replied over at AAC.