The Smell of Molten Projects in the Morning

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Doorbell Switch Re-LED-ing

Having had several folks ding our front doorbell in recent weeks, I thought it would be nice if the switch had a light inside and was mildly surprised it didn’t. Taking it apart revealed an even bigger surprise:

Doorbell - circuitry
Doorbell – circuitry

Much electronic! Many solder!

Obviously, that’s a bridge rectifier (MB6S for the curious) in the middle, with a pair of paralleled 1 kΩ SMD resistors on either side ballasting two white LEDs in series on the other side. As far as I could tell, both LEDs had stopped being diodes, most likely after one failed short and took the other down with it.

Having recently unpacked the small parts cabinet containing SMD LEDs, I could do this:

Doorbell - blue LEDs
Doorbell – blue LEDs

While I had the iron hot, I resoldered the fractured blobs attaching the spring contacts to their solder pads. I think the 201107 along the left edge is the PCB date code, so the switch has been in place for maybe a decade.

You gotta admit blue is distinctive:

Doorbell - installed
Doorbell – installed

While taking it off, I discovered it’s the second doorbell button in that spot; you can’t see the bottom screw hole and wood scar when you’re standing at the door. Unless, I suppose, you’re three feet tall, but most folks of that stature aren’t curious about doorbells.

Update: An alert reader provided more information:

I recently bought a doorbell button, Heath Zenith SL-315-1-90. […] My board is different but has the same circuit as yours. In case it’s helpful, I believe your button might be Heath Zenith SL-257-02.

That’s a perfect example of a “brand name” completely detached from its entire history and put to work doing something entirely different. AFAICT, I honored the Heath name by resoldering the poor thing.

Alas, the doorbell switch on the back door turned out to be a dead loss. Perhaps when they replaced the door, the wire got sliced just above the sill plate, leaving a stub in the basement and no way to fish a new wire to the switch. Anybody arriving via the trail from the Vassar College property out back must bang on the door to get our attention.

Comments

6 responses to “Doorbell Switch Re-LED-ing”

  1. Brent Avatar
    Brent

    Good to see you back.

  2. David Avatar

    When the old fashioned lamp failed in my doorbell switch, I replaced it with a blue LED. Plus a diode to control the reverse voltage and a resistor to limit current.

    1. Ed Avatar

      That’s exactly what I planned to do. Imagine my surprise at finding it was already done, just dead!

  3. david Avatar
    david

    Wow! That is some Extremely Robust and Well-Crimped wiring. A shame they’re entirely the wrong size for those screws…

    1. Ed Avatar

      Pretty fancy, eh?

      That’s the widowmaker end of a line cord plugged into a variable isolation transformer set at 19 VAC to match the doorbell transformer, because I hadn’t been able to find the Box o’ Bench Supplies or the test leads. One of these days I’ll find everything …

  4. Mailbox Post Repair – The Smell of Molten Projects in the Morning Avatar

    […] One doorbell ding came from a guy who sheepishly admitted he had just collided with our mailbox, which sits on the outside of a gentle curve and sticks out, IMO, a bit too far into the street. […]