LED Lighting a Trimphone dial...

[twocvbloke]

First off, the LEDs I got, they're not the nice phosphor green I hoped for like with the LEDs I played with initially, so this is just a "prototype", haven't wired them up (or worked out how to!) for line-voltage use, so they're running on low voltage DC...

Boy was it an absolute pain to wire these LEDs together though, had to snip them, remove the varnish/enamel coating from the wire, solder them together in parallel, feed them into heatshrink tubing and carefully bend the whole thing into the right C shape to fit the dial, all in all it took me about 4 hours from start to finish, soooooo, I don't think I'll be taking any orders for these, at all... 

I've ordered another string of Multicolour LEDs which from the pictures appear to use Gallium Nitride LEDs, which are what are on the multicolour string I initially played with, so fingers crossed, those ones will be the right colour, and I can wire them up in Series (saves time with snipping & stripping too) to have them run from line voltage with some assistance of resistors...

Anyway, pics, first two pics are the LEDs running off the Diode test voltage from my multimeter, so produced a nice low-level glow, just not in the right colour (for me anyway!), third picture is running the LEDs off a 3v battery pack, very bright indeed, camera's white balance makes it look like the "right" green, but in person it's still the same green as the first pics, and the fourth & fifth are looking at the LED tube blu-tacked into the dial...

[Key2871]

Can you add resistor to your power source to lower the input voltage more? If your running 3volts now, and you have no resistor, I think adding one about 50-75 ohms would bring it down more, to a more desirable level.
But so far it's looking nice, but I can see where you wouldn't want it that bright.

[twocvbloke]

I can use resistors to lower the input, yes, but I have plans to use line voltage, and 48v to 2-3v is a lot to drop, so wiring the next batch of LEDs in series would mean they'll need 20-30v to power them, much less to drop from line voltage...

[19and41]

That looks nice!  As an aside in thinking how the original appearance could be retained with LED's, I was thinking of a lucite (perspex) rod heated and set in a circular form  with 2 high brightness green LED's at each end facing into the tube, edge lighting it and have one side of the lucite circle, the part beneath the dial lightly sanded.  It would concentrate the edge lighting along the sanded area and have the appearance of an glowing tube.

[twocvbloke]

I'd thought about fibreoptic type illumination options, and some of them are seemingly easier, but I'm just doing this for experimental (mostly mental) reasons, I haven't got a whole trimphone to sit the dial in, so it's just a play project to open up another option for reviving the glow...

[Owain]

I can use resistors to lower the input, yes, but I have plans to use line voltage, and 48v to 2-3v is a lot to drop,

On-hook, but off-hook it's a lot lower, and you'd need the lights to work off-hook as that's when you'll be dialling.

[Key2871]

Right off hook the voltage is around 5 volts, so that's not too bad, but you will want a larger resistor.
Good luck with your phone!

[Jim Stettler]

Right off hook the voltage is around 5 volts, so that's not too bad, but you will want a larger resistor.
Good luck with your phone!

I would use a pot (adjustable resistor) to experiment with. Once you get everything set up, you can measure the resistance of the pot and install a regular resistor.
Just an opinion,
Jim S.

[Key2871]

Yes, but it could get hot and burn out. But that would be a good idea.

[Jim Stettler]

Yes, but it could get hot and burn out. But that would be a good idea.

The point I was attempting to make was, use a pot as a tool to determine approximate resistance.
I said for experiment. You dial it in and measure.  It would take a very long time to get hot enough to burn out as a bench tool.
You could also dial in a nice low level light and check ohms. Then a high level, check again and split the difference based an a standard resistor.
Please keep in mind these  are  proto-type experiments preformed by interested collectors for their own enjoyment. It is how many of us entertain ourselves.
JMO,
Jim S.

[twocvbloke]

Well, the On-hook versus Off-hook voltage has thrown a spanner in the works a bit, so that's something else to figure out...

As for the whole experimenting thing, yes it's just something I'm playing with, if it works, great, if not, I've passed some time doing some learning along the way, which is what I enjoy doing, and also helps serve up ideas for others who want to re-illuminate their Trimphone dials without resorting to shelling out on expensive small tritium vials...

[Key2871]

Jim, I understand what you were saying. My point was depending on the quality of the pot it may not last long enough for a reasonable reading.
But I do agree it would help narrow down the ohms needed to get better results.

And off hook voltages can be different in other areas / country's.

[19and41]

I keep a wirewound pot with clip leads to perform test functions.  They are also handy for simulating components in automotive and other electronic sensor testing.

[Key2871]

Excellent, wire wound is the way to go.
Thanks. I had forgotten about those puppy's.

[HarrySmith]

Maybe a stupic question bit what is a wirewound pot?
I am guessing some special kind of potentiometer?
Never heard that before and I have been working on cars since I was 12 years old.