On 4/24/2013 11:38 PM, gregz wrote:
The Daring Dufas wrote:
On 4/24/2013 10:07 PM, wrote:
On Thu, 25 Apr 2013 00:35:46 +0000 (UTC), gregz
wrote:

wrote:
On Tue, 23 Apr 2013 16:35:10 -0500, "ps56k"
wrote:

Our doorbell is the standard one with the small rectangular "illuminated"
button,
that is screwed to the door frame.
Every so often, usually just prior to Halloween
I go out and replace the button - as the tiny bulb has burned out.

Wonder if there are any LED style replacements ?
I had seen some comments on an electronics forum
about how you might contruct one -
but was curious if any retail versions existed ?

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.

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.

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.


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

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


Years ago I was building remote trouble annunciators for the Generac
power systems I was installing and I was using the new (back then) 10mm
super bright LED's I picked up from Radio Shack. I put the big LED in
series with a 5 volt DC 5mm red blinking LED and in series, the current
draw was within limits at 12 volts DC. You can see the light from the
big red LED flashing on the opposite wall of a garage. The annunciator
goes off when the genset trouble output goes active. You can push the
silence button to stop the noise but the big red flashing LED is
obnoxious enough that you don't forget to call for service. I actually
got a call a few years ago from a service guy who was working on one I
installed 15 years earlier. ^_^

TDD