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Will this work safely?

Started by Terry Pinnell August 24, 2019
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:

https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1

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
On Sat, 24 Aug 2019 20:12:52 +0100, Terry Pinnell
<me@somewhere.invalid> wrote:

>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: > >https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1 > >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
Anything with mains is not safe for you. Use batteries or let it be. w.
Helmut Wabnig <hwabnig@.- --- -.dotat> wrote:

>On Sat, 24 Aug 2019 20:12:52 +0100, Terry Pinnell ><me@somewhere.invalid> wrote: > >>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: >> >>https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1 >> >>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 > > >Anything with mains is not safe for you. > >Use batteries or let it be. > >w.
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
On 2019-08-24, Terry Pinnell <me@somewhere.invalid> wrote:
> 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: > > https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1
404
> 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.)
The hard way: so they are using a capacitive dropper to power the chime circuit?
> 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.
That'd work, but an audio transformer might be cheaper and more compact, but nothing is cheaper than junkbox...
> Can I now safely experiment with that?
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.
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. 
Jasen Betts <jasen@xnet.co.nz> wrote:

>On 2019-08-24, Terry Pinnell <me@somewhere.invalid> wrote: >> 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: >> >> https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1 > >404 > >> 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.) > >The hard way: so they are using a capacitive dropper to power the >chime circuit? > >> 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. > >That'd work, but an audio transformer might be cheaper and more >compact, but nothing is cheaper than junkbox... > >> Can I now safely experiment with that? > >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.
Thanks Jason, that's helpful. Sorry about the 404. Not sure of cause but have re-posted and now looks fine here. https://www.dropbox.com/s/wtgfyyfeo3x5ls1/Sketpg?raw=1 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
On Sat, 24 Aug 2019 22:39:37 +0100, Terry Pinnell
<me@somewhere.invalid> wrote:

>Helmut Wabnig <hwabnig@.- --- -.dotat> wrote: > >>On Sat, 24 Aug 2019 20:12:52 +0100, Terry Pinnell >><me@somewhere.invalid> wrote: >> >>>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: >>> >>>https://www.dropbox.com/s/xvvhz7pnnsdbpc2/DoorBellExtensionSketch.jpg?raw=1 >>> >>>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 >> >> >>Anything with mains is not safe for you. >> >>Use batteries or let it be. >> >>w. > >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
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.
On Saturday, August 24, 2019 at 12:12:56 PM UTC-7, Terry Pinnell wrote:
> 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 ...
> 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.
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.
On 26/08/2019 1:58 am, whit3rd wrote:
> On Saturday, August 24, 2019 at 12:12:56 PM UTC-7, Terry Pinnell wrote: >> 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 ... > >> 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. > > 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. >
Yep the old opto isolater trick, that's your answer to the prob.
Terry Pinnell wrote:

> 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. > >
** 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