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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Dec 2019, 11:42 am   #1
Nickthedentist
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Default Driving a piece of electroluminescent tape in lieu of a magic eye

Hello everyone,

I have a few shabbier radios which have magic eyes with zero emission, but which don't really merit spending a lot of money on a replacement.

A black void where the glow used to be looks rather sad.

So I thought of using a bit of EL tape in its place, masked to replicate the shape of the original eye's target. Not functional, purely for aesthetic reasons.

Q1. Can the lengths of EL tape available on eBay etc. be cut into multiple pieces, and each bit utilised?

Q2. What are the typical drive voltage requirements, and can this be obtained from a valve set without resorting to a separate transistorised driver?

Many thanks,

Nick.
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Old 2nd Dec 2019, 12:26 pm   #2
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

I'm sure I've seen a project somewhere with seperate segments of tape used, so I would say that is OK, just a matter of interlinking the pieces.

Voltage wise - 120VAC rms (can go higher), 50-2000Hz.

Higher voltage = brighter display but shorter life, same with frequency - yes, this stuff does "wear out".

Haven't played with this stuff quite a while now, was playing about with using it as backlighting in some moving coil meters.
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Old 2nd Dec 2019, 12:33 pm   #3
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Thanks Terry, that's very helpful.

Presumably the current drawn is pretty negligble?
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Old 2nd Dec 2019, 2:47 pm   #4
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

I think Philips tied their EL scale plates directly to the hv winding of the transformer, though I seem to remember that a somewhat higher frequency is better. They didn't live too long anyway, but modern technology is probably better. You could tie a modern EL material to the 120V winding through a resistor. Most important is a symmetrical wave form.
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Old 2nd Dec 2019, 2:59 pm   #5
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Thank you too Maarten.
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Old 2nd Dec 2019, 3:07 pm   #6
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

I've thought about this 'fake magic-eye' thing a bit in the past - rather than using electroluminescent stuff I had the idea of using a disc of relatively-thick Perspex/Plexiglass/Lexan or similar, with both faces very finely abraded [2400-grade wet&dry paper] so they're matt and act as a diffuser, then place a green LED behind it.

I even pondered using a few milliamps 'stolen' from the output-valve's cathode to light it: maybe add in an AGC-controlled FET to vary the brightness of the LED to better replicate the function as a tuning-indicator.. Modern green LEDs are really rather bright even at 5mA!
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Old 2nd Dec 2019, 3:51 pm   #7
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

I like that idea too and will give it a try.
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Old 2nd Dec 2019, 4:47 pm   #8
Alistair D
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Solid state magic eye replacements have been discussed a few times. A lot more work than a simple bit of glowing tape but give a more realistic result.

https://cse.google.com/cse?cx=008872...h+this+website

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Old 2nd Dec 2019, 10:40 pm   #9
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Quote:
Originally Posted by Nickthedentist View Post
Thanks Terry, that's very helpful.

Presumably the current drawn is pretty negligble?
I actually had to look that up - most places are quoting 0.14mA/cm2 but not listing what voltage/frequency that was measured at.

A possibly better material than tape would be Electroluminescent Panel (same principal) as it can be cut (carefully) to any shape needed.
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Old 3rd Dec 2019, 7:23 pm   #10
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Subject to possible interference, a 1" green OLED might be suitable with an 8 pin ATtiny driving it.
example only:-
https://www.youtube.com/watch?v=5Y9L4SADUDg
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Old 3rd Dec 2019, 7:57 pm   #11
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Or an arc of small green LEDs behind a translucent screen, with that old favourite the LM3914 IC driving them to give a pseudo-representation of a 270-degree 'meter' scale?

[The LM3914/15/16 - though an IC - counts as vintage! NatSemi released it in 1980!]
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Old 3rd Dec 2019, 9:48 pm   #12
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Every now and then, it's possible to find ex-Soviet miniature (sort of 1" to 3cm range) CRTs being sold for not a lot on the auction site- I'd toyed with the idea of messing around with one of these to see if it would make a magic eye alternative. If the existing HT isn't enough to make a significantly bright trace, a sniff of secondary AC could be doubled as only tens or low hundreds of uA would be needed including the biassing chain. Probably unwise to go beyond a few hundred volts to avoid undue beam stiffness and low plate sensitivity. The appropriate amount of secondary AC could be applied to one set of plates to generate a de-focussed (i.e. both broad and non-burning) line in one plane with AGC being used to deflect it in the other plane. Things like whether to run elevated cathode (beware heater) or anode would need to be thought about, with necessary level-shifting applied to plate drive (involving not too much complexity with not too many small HV transistors). There's probably a glaring flaw in this scheme that I haven't spotted yet!
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Old 4th Dec 2019, 12:33 am   #13
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

If you really want to get a good representation of a magic eye, an arduino and tft or OLED screen could be used to display an actual moving picture of one.

You do of course have to work out how to mount all this, but the OLED screens do come in an approx 1" size (digital hash could be a problem in some cases).
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Old 6th Dec 2019, 12:25 pm   #14
David G4EBT
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

I think the best compromise I've seen over the years is the one that Joe - 'Pillenwerfer' -posted a link to at post #7 in this forum thread in Summer 2017.

https://www.vintage-radio.net/forum/...d.php?t=137110

It refers to a PIC driven circular array of fifteen green LEDs is a 300 degree arc, with a red LED at the bottom. The power for the project is derived from the rectified 6.3V heater supply of the valve. It had been mentioned in forum thread back in 2016 (which I can't now find) and I got as far as building one, but the project stalled as I was unable to get the PIC programmed. (See post #8 in the above link). Full constructional details are at the link below, including the source code for the PIC:

http://electronbunker.ca/eb/6U5.html

The circular LED array is still available cheaply from China on ebay, described as '1.3" Annular LED Ring Display Green Bars & Red Dot (Rotary Encoder or Clock)'

https://www.ebay.com/itm/251437248842/

$4.18 USD inc free post. (Just over 3.00 GBP).

I wondered if anyone on the forum has built the project?

If not, and anyone is able to program the PIC and would like to have a go at building the replica eye, I do have a spare PCB that I etched, and two unprogrammed PICs, which I'd happily exchange on a 'quid pro quo' basis for programming a PIC for me. Alternatively, if someone could program a PIC which I'd supply, I'd be happy to recompense them.

The pic below is how far I got with the project. I don't actually need an eye at present - I just thought it was an interesting project so built it on impulse as I've been prone to do over the years if something takes my fancy. Too easily distracted - too many half-built projects. Probably undiagnosed ADHD or some such thing.

Hope it's of interest.
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Old 6th Dec 2019, 6:33 pm   #15
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Default Re: Driving a piece of electroluminescent tape in lieu of a magic eye

Thanks for jolting the memory on that project David- I'd forgotten about those LED collars for rotary encoders, one of those behind something like translucent Perspex would make a nice facsimile of magic eye action. I'd chewed over using a LM3914 to drive it, with two arcs of 7 LEDs on each side sweeping upwards to close the shadow but I see that the display is multiplexed and would need electronically "unstitching", so a simple circle of separate LEDs would make more sense if not using a PIC. At least the LM3914/5/6 family continue to be widely available, they must be one of the most popular "project" ICs over the years,

Colin
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