Will this work safely?

Pressing the door button of my commercial wireless door bell causes the mains-powered speaker unit in the hall to chime. Rather than buying another speaker unit I thought I'd make a simple extension myself. I'd then get an identical chime in my workshop.

With difficulty I was able to get access inside the unit and connected a couple of wires in parallel with its tiny speaker, like this:

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I was playing with connecting that pair to a simple audio amp powering a newly located speaker in my workshop. That's when I quickly discovered (the hard way!) an obvious flaw in my idea. Both wires were at half mains voltage above earth. (Which is 0V/ground for most of my circuits.)

So I now propose to isolate that with a small mains transformer. One that I have to hand is a 240V to 18V, with respective DC ohm measurements of about 900 and 30 ohm respectively.

Can I now safely experiment with that?

Terry, East Grinstead, UK

Reply to
Terry Pinnell
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Anything with mains is not safe for you.

Use batteries or let it be.

w.

Reply to
Helmut Wabnig

Eh?

Have you ever used a transformer? In the 40 years or so that I've been building electronics stuff, I don't think I'd have accomplished much without "mains"!

Terry, East Grinstead, UK

Reply to
Terry Pinnell

404

The hard way: so they are using a capacitive dropper to power the chime circuit?

That'd work, but an audio transformer might be cheaper and more compact, but nothing is cheaper than junkbox...

If the mains transformer is double insulated, then yes, if not ground the output then it's safe, it's probabaly best to ground it in the workshop: I seem to recall your location having some voltage difference between ground in the house and in the workshop.

--
  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

I quite qualified advice is for you to stay away from the mains. What's more, you can't just run that anywhere you want no matter where you are.

You want to extend those mains you need to know how to put pires in boxes and all that.

If you do it after all that then you can just use regular [phone wire. You should do that.

get a transformer, 1:1 would be good but rated for mains isolation just in case and wire that to the speaker. The wires from the secondary should drive another speaker. Nice thing about that is you can run those wires anywhere.

When you get to anything running off the mains you need to know how to deal with it, maybe even run conduit. You obviously don't and I figure it is better not to kill yourself.

Digikey deals there I think, they can probably hook you up with the transformer for a few bucks. If not you got somebody there.

Just stay away from the mains. I work on that stuff sometimes and I have seen wires arc and spark, and even burn. I have been shocked pretty good, but you got 230 over there.

No matter what, stay away, you could kill yourself or burn the place down.

Reply to
jurb6006

Thanks Jason, that's helpful. Sorry about the 404. Not sure of cause but have re-posted and now looks fine here.

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Re capacitive dropper. Yes, but unsurprising in a unit like this? Essentially a mains plug with some extras. After all, its innards are plainly not intended to be accessed by electronics hobbyists ;-)

I hadn't finalised my design for the add-on. I was in the process of bread boarding a basic LM386 audio amp, with an independent (mains-powered) 12V DC supply. I suspected that merely paralleling to the remote speaker would reduce audio volume from both of them. That's when I was unceremoniously reminded that my basic assumption was loose thinking! (Namely, that because the existing wires were to a 16 ohm miniature speaker, with a DMM-measured output during chiming of 3-4V AC, I could safely wire them up to any old DC circuit.)

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Why are you asking stupid questions when you gave 40 years of experience.

Your question is that stupid, that I issued a warning rather than an answer.

w.

Reply to
Helmut Wabnig

Easiest way out of that would be an optoisolator solution (there are dual isolators that can be used with some feedback to transmit analog signals). Or, using either a relay or digital optoisolator, you can trigger a sound-playback of your choice (there are a number of battery toys at the local dollar store that do sound effects). Heck, there's greeting cards that can be programmed to replicate your favorite annunciator's sound.

When light-dependent players were built into Christmas-y coffee mugs, an EE of my acquaintance noted that she could 'fix that' with her microwave oven.

Reply to
whit3rd

Yep the old opto isolater trick, that's your answer to the prob.

Reply to
Rheilly Phoull

** By far the cheapest and easiest solution is a second door bell unit - set to use the same coder as the first

What you are attempting is unsafe, expensive and trouble prone.

IOW completely nuts.

..... Phil

Reply to
Phil Allison

For him.

If I remember right, for the hard of hearing they used to have a doodad you stick on your phone and when it rings it lights a light. Probably can't get them anymore but the thing is while I could do it right dealing with the mains, I doubt the OP can.

So the best way to proceed is to detect the noise, right at the box. A cheap piezo mic will do. It can drive whatever, even pick up the sound and put it on the wire.

Using the mains, well first of all you got a whole bunch more rules dealing with that. Second of all you still need something to feed off it. This is all easier with low voltage.

Reply to
jurb6006

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