An interesting magic eye substitution

[jim_beacon]

Originally Posted by YC-156

An EM34 only takes 200mA. Still, that should suffice.

You could always pulse the individual LEDs in sequence, as you would in a mutilplexed 7 segment display - this would dramatically reduce the average current.

Jim.

[YC-156]

Originally Posted by jim_beacon

You could always pulse the individual LEDs in sequence, as you would in a mutilplexed 7 segment display - this would dramatically reduce the average current.

Not to worry Jim, I've been doing this for a living. Progress on this little project has so far been limited by my usual supplier here in town not having any suitable PICs in stock, so I will have to wait for the shipping delay.

Frank N.

[XTC]

I don't see that powering this device is the main problem.

Mains transformers are not usually so tight that you can't pinch an extra 100mA of heater current.

In most cases you could fit a small mains transformer somewhere in the cabinet that would deliver 1 amp at 5V which should be more than enough.

It would be far neater to have it as a plug-in replacement for the original though.

Something that might be a nuisance is the RFI from the clock.

Pete.

[YC-156]

Well, since the cat is already out of the bag I might as well post the rest of my ideas for making an EM34 substitute.

What I have in mind is:

• A self contained plug in replacement, including its own, internal PSU. Will be a bit of a squeeze, but I believe it will fit.
• Prototype will probably use a PDIP, but the real thing will use a PIC87F871 in a 44 pin PLCC. Even accounting for a socket this should fit. The main problem at the moment is actually a pair of electrolytics for the PSU, but I haven't yet researched the sizes of readily available SMD caps. Need to test a prototype before I can nail the actual capacitances required.
• Current consumption of the PIC is negligible at the clock frequencies required, so the LEDs will eat the most. Accounting for a bit of losses in the PSU (+/-5V), then we could simultaneously drive 8 LEDs at 10mA through each for a total consumption of around 100mA. From testing even the weakest green LED in my junkbox this seems to be plenty for all but perhaps direct sunlight, assuming you smear this 'light power' out across a few square cm.
• True symmetrical PSU circuit. Ie. no DC current component on the 6,3V line.
• 32 pieces of green 5x2mm LEDs arranged in a circle. They have to be ground down a bit to fit the shape of an EM34 reflector.
• Dual sensitivity with a response curve closely resembling that given in the EM34 datasheet.
• Left- and rightmost LEDs are always full on (but see below) as power indicator. They can be driven by the same pin on the PIC. There are 33 I/O pins available, but one is required for the AGC line input for the ADC and another is needed for the...
• Ambient light sensor, used for continuously adjusting the duty cycle of the PWM waveform. This will make the LED eye more useful in daylight, while providing for a balanced light output at night. Should have a very long time constant, say 64 seconds, to ensure the LEDs doesn't flicker at the slightest provocation. The phototransistor can conveniently be located in the dark center portion of the front.
• Slow turn on at power-up. After reboot you get 15 seconds or so of nothing, followed within the next 15 seconds by a linear ramp-up to the level dictated by the ambience.

Originally Posted by XTC

Something that might be a nuisance is the RFI from the clock.

That is why they invented thin copper foil (or a piece of Aluminium piping) and the feedthrough capacitor. If the electronics of the eye is built inside a cylinder with a bottom cap, the waveguide effect will ensure that virtually no RFI 'escapes' out through the front opening.

But I plan to take this one a step at a time. First a breadboarded prototype as proof of concept. Then, depending on how convincing the results are, I may build a 'genuine' replacement in the EM34 form factor. I have been looking for an excuse to play around a bit with today's embedded controllers, and this application looks perfect.

Anyone having a dead Octal valve with the small diameter base they want to part with, please?

Frank N.

[Dave Moll]

Originally Posted by YC-156

Anyone having a dead Octal valve with the small diameter base they want to part with, please?

What diameter is small?

I have a dead VT52 which appears to be about 28mm diameter of outer and 20mm across the pins. One complication - it has no pin 6. May be possible to extract pin 1* (N/C on EM34) and relocate it.

*perhaps it needs the services of our resident dentist

edit: I've just noticed that there are two types of VT52 - mine is the one with the octal base (labelled VT52(RAF) in TDSL.

[YC-156]

Originally Posted by Dave Moll

What diameter is small?

28mm! 'Large' is the size of an EL34 base, 31,5mm.

Originally Posted by Dave Moll

I have a dead VT52 which appears to be about 28mm diameter of outer and 20mm across the pins. One complication - it has no pin 6. May be possible to extract pin 1* (N/C on EM34) and relocate it.

No need. Pin 6 on an EM34 is A2, D2. These will be NC in my construction, since I only need the low voltage pins: 2, 4, 7 and 8.

So if it is surplus to your requirements...? Maybe we should save on the shipping until I'm sure I have a design, which will fit.

Best regards

Frank N.

[ppppenguin]

Originally Posted by YC-156

PIC87F871 in a 44 pin PLCC. Even accounting for a socket this should fit. The main problem at the moment is actually a pair of electrolytics for the PSU, but I haven't yet researched the sizes of readily available SMD caps. Need to test a prototype before I can nail the actual capacitances required.

Frank, sounds like you've thought about this pretty carefully. May I add some extra thoughts:

• Consider using a QFP package processor since this is smaller than PLCC in a socket. The snag is that the PCB will have to be surface mount with fine tracks.
• Modern electrolytics are pretty small. Even 220u low voltage parts, especially SM types, are small. Even if you have some hum on the power supplies I doubt this will trouble the processor or LEDs though it might cause a beat effect with the LED switching if you use any form of multiplexed drive.

PS: I've just measured a 100u 6.3V SM part and it's about 6mm diameter and 5mm high.

[Brian R Pateman]

A further thought -

RS stock "electroluminescent film" in various colours.

It looks as though one supplies it with 20 / 200 volts and it glows in a fairly satisfactory manner.

I haven't played with it but I'll add some to my next order and report back.

Regards,

[Dave Moll]

Originally Posted by YC-156

So if it is surplus to your requirements...? Maybe we should save on the shipping until I'm sure I have a design, which will fit.

It's certainly no use to me - detached top cap leaving 2mm hole; lots of white getter oxide inside. But I knew there would be some reason not to throw it away. Yet again my hoarding of "junk" has been vindicated

I will wait until I hear from you before shipping it.

[YC-156]

Never mind...

A friend just came by and dropped off (not literally) the recently acquired set for which I was sure I would need this gizmo. Something worthy of an extra effort I would like to believe.

Did I ask the seller if he would package it carefully?
Did I offer to pay (quite a bit) for 'extra care in packaging'?
Did he tell me that this certainly wouldn't be needed?
Did he stuff the poor thing (all 18kg of it) in a thin cardboard box about 2cm larger than the set in all directions and stuff it with curled up newspaper so hard that you had a near 1:1 transmission of forces from the box to the sides of the radio?
Did this predictably break the (probably irreplaceable) dial glass into four pieces?

[evingar]

Deepest condolences.
Posting vintage equipment is such a lottery unless the person posting is a fellow enthusiast – but sometimes it’s a gamble that is difficult to avoid.

[YC-156]

Thanks Chris,

Well, hope I don't drift too far off topic here, but after closer examination I'm not sure this cannot be mended. While there are actually five main pieces plus all the tiny shards, it just might be possible to glue this back together, followed by a touchup to the paintwork on the back. Due to the location of the cracks it might not be that visible, once everything is back together.

I happen to know a genuine glass craftsman, but I suspect he will rob me blind for fixing this puzzle.

But I'm afraid my EM34S(emiconductor) project is on hold for now.

Brian,
It would be quite interesting if they can be cut up into smaller pieces. If so, then they might be an interesting alternative to LEDs.

Jeffrey,
My reason for choosing a PLCC was that I would like others to be able to copy the project if they wish. To that end I prefer only to use SMDs as a last resort, and a PLCC plus socket will fit, if only barely.

The caps I probably need are something on the order of 1000uF/16V and ripple is not the issue here, supply current is.

Best regards

Frank N.

[Paul Stenning]

Please bring this back on topic, or it'll be closed. Thanks!

[Brian R Pateman]

Originally Posted by YC-156

It would be quite interesting if they can be cut up into smaller pieces. If so, then they might be an interesting alternative to LEDs.

According to the RS catalogue the sheet can be cut into smaller pieces. I will order some (it is quite cheap - for RS) and have a play.

Regards,

[XTC]

EL film is interesting.

I assume the Konica ad at the foot of this page is made of it and it looks a bit like a magic eye.

http://world-electroluminescent.com/EL_light.html

Pete.