doorbell - is LED avail

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On 4/24/2013 7:26 AM, bob haller wrote:

I see gear older than me with a sad little neon pilot light barely flickering but it's lit. ^_^
TDD
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On Tue, 23 Apr 2013 19:48:59 -0400, "John Grabowski"

You can buy all the diodes you want at Radio Shack. My "musical doorbell" (electronic) came with both the instructions detailing the need for a diode as well as a little package with two diodes in it.
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ed"

two

go

be

but

when buying diodes higher current rating and voltage never hurts. in continious duty the higher current rating is usually larger physically which helps keep it cool for long trouble free operation.
generally doubling voltage and tripling current rating is a good idea, plus diodes are very cheap:)
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wrote:

The only time there is any significant current is when the doorbell is ringing. It's a pretty short duty cycle. I"m not disagreeing with your general statement but this is not a very stressful application.
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geezI never had a liighted buttons bulb burn out.
Your transformer voltage may be too high
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I think you just have good luck or a well designed unit.
Greg
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wrote:

I don't think I've ever had a button burn out either. I'm on my second button and the house is 34 years old, but I think the house came with an unlighted button, so I changed that almost right away, and after 15 or 20 years, the new button got so weathered the light didn't show through. (Or maybe it burnt out but it was still after 15 or 20 years.)
I bought the 2nd button at Home Depot. It's just like the first one, pretty much the cheapest lit button that they sell, other than the round one that goes almost entirely in the hole. (This is a black plastic rectangle which sits on top of the wood, with a metal cover that wraps around the top, front, and bottom, with a white or cream colored plastic button in the middle**.) . When I put in a doorbell in the basement, in parallel, I had to put in a bigger transformer, so I got either 16 or 18v (whichever the bigger doorbell transformer is) from Home Depot. In other words nothing special.
The OP's voltage may be too high. Maybe the previous owner didn't use a standard doorbell transformer. Or maybe it's broken.
**Actually all the buttons by the same maker are probably of the same quality, just the cases are different. I know in 1967 when my car compass didn't work, I wrote to Airguide, I think the name is, and asked if I bought a more expensive compass would it work better? And they wrote back, "No. All the compasses are the same. Only the cases are different."
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On Tue, 23 Apr 2013 16:35:10 -0500, "ps56k"

If they dont sell them, find one where you can access the bulb. Wiring a LED would be simple. Your doorbells are usually running off a 24v AC transformer. So, you'd need a diode to convert to DC, then a suitable resistor (someone on one of the electronics newsgroups could help with selecting the right size), and of course the LED itself (probably white). 3 parts, and a little solder, and you'll have a LED lighted doorbell.
To wire it, one power lead goes to the diode, then to the resistor, and to the LED. The other lead on the LED goes right to the power wire. Polarity of the LED and diode are important. There are likely lots of simple circuits for them on the web. Or buy it at Radio Shack and there will be a wiring diagram on the package.
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It's nice to include a diode, which limits current in one direction, and also stops reverse current, but it will work without diode. Done it many times.
Greg
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wrote:

I didn't know that. I thought it was needed on AC power. Now that you mention it, I worked on a set of xmas LED lights and never saw a diode either.
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The Xmas lights might not ever go reverse current because I'm pretty sure it's higher than forward voltage to conduct. I don't like the look of blinkys. A bridge rectifier would double the frequency.
Greg
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I would not just add a bridge without testing. The LEDs might get too hot.
Greg
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On 04/24/2013 09:42 PM, gregz wrote:

A bridge would increase the efficiency a little. Probable too little to be concerned about here. If you do use one, consider that it adds an about 1.4V voltage drop.
I wouldn't use a bridge here, because of the increased complexity and reduced reliability.

Unlikely unless current was excessive (resistor too small).
BTW, I have (accidentally) connected 12V (1.5A supply) to a LED without a resistor. It popped and split in half immediately.

--
Mark Lloyd
http://notstupid.us
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On 4/25/2013 1:46 PM, Mark Lloyd wrote:

Terrorist! LED's everywhere are in fear for their lives. ^_^
TDD
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On 04/24/2013 09:38 PM, gregz wrote:
[snip]

Maybe not.
AFAIK, the reverse threshold (voltage that must be reached for a diode to conduct) is usually higher (AFAIK) than the forward voltage.
If there is ever any reverse current, it'll be too small to be concerned about.
--
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On 04/24/2013 08:37 PM, snipped-for-privacy@internet.com wrote:

For xmas LED lights, the series I've seen have 25, 30, or 35 LEDs. Longer strings have multiple series, in different polarities. These have diodes. That's what LEDs are.
However, some LED strings seem to have full-wave rectifiers (4 diodes) in them, in addition to the LEDs.
--
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On Apr 24, 8:37 pm, snipped-for-privacy@internet.com wrote:

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They put a diode and/or a resistor in a little lump somewhere in the power cord or in the string of lites itself.
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wrote:

How does a diode "limit current"? Without an anti-parallel diode, an LED will be toast. They won't take more than five or ten volts reverse.
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On 4/24/2013 10:07 PM, snipped-for-privacy@attt.bizz wrote:

I thought a regular 5mm red LED used 2 volts DC at around 30ma. A small switching diode rated at around 50 volts DC and a suitable resistor to limit the current with everything in series with the LED should work across the doorbell button since it's working as a simple continuity indicator across an open switch but in series with the doorbell and power transformer. ^_^
TDD
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Right, but 30 ma can be too bright with current LEDs. The very large LEDs which can take amps, are surprisingly bright at less than 50 ma. These have higher forward voltage levels,2-4 volts.
Greg
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