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Making a 13" TV bluetooth enabled
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JP in Wisconsin
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PostPosted: Thu Dec 20, 2007 3:58 am    Post subject: Making a 13" TV bluetooth enabled Reply with quote

Hey everyone - looks like I've found the right place to ask this kind of question.

I've got a 13" TV in our exercise room that I want to make bluetooth enabled - we have 2 small kids and the exercise room can be like an echo chamber when I'm working out and trying to watch something on the TV.

But the situation is this:

I have the bluetooth headphones and a bluetooth transmitter, both made by Jabra, and the transmitter is a 3.5mm plug. Problem is, the TV does not have an audio out plug to plug into.

Because it's not the nicest TV, I'm not worried about marring the exterior of the box to remedy this. My plan is to remove the case and drill a hole to install a 3.5mm jack.

My question to you electronics gurus out there is this - if I redirect the wires that were leading to the single mono speaker to this jack, do I need to worry about the amount of current going into the jack? If so, is there something I should add inline to reduce the current?

Thanks in advance for your help. Very Happy
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Thu Dec 20, 2007 8:25 am    Post subject: Reply with quote

A word of warning: many cheap, small televisions have a power supply that is not isolated from the electrical mains. This is usually true for the models that have no audio or video inputs/outputs at all, just an antenna connector.

On a such television, the leads to the loudspeaker will carry the mains voltage (or half the mains voltage) to ground, and it is completely unacceptable from a safety point of view to connect it directly to a 3,5 mm jack.

In this case, an isolation transformer must be connected between.
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JP in Wisconsin
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PostPosted: Thu Dec 20, 2007 3:24 pm    Post subject: Reply with quote

Thanks for the tip.

If I put a voltmeter on those leads, what's a reading over which I'd need an isolation transformer?
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hirollcenter



Joined: 19 Dec 2007
Posts: 5
Location: bluegrass

PostPosted: Thu Dec 20, 2007 5:21 pm    Post subject: blue tooth Reply with quote

If you have the volume turned all the way down you should see 0(no voltage) as you turn the volume up,the meter should start showing some voltage,use the a/c input on your meter since audio is an a/c sine wave, depending on the wattage of your speaker ampifier the max voltage could be under 10 volts.Also the meter will not show a constant voltage due to the varing of your audio signal, if you see half of your primary voltage you will need a audio isolation transformer.mine you this is different then a regular isolation transformer for your a/c...dls
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Thu Dec 20, 2007 10:14 pm    Post subject: Reply with quote

You should be able to go to radio slut and get a head phone jack. Just tap off of the speaker. It will only get tricky if you try to wire it to disable the sound on the set when plugged in.
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JP in Wisconsin
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PostPosted: Fri Dec 21, 2007 4:39 am    Post subject: Reply with quote

Yup, I already did that - though the clerk clearly wasn't well versed in what his store was about, besides their move to cell phones and cordless phones. But I found a little packet of jacks with soldering posts.

Which reminds me - which lead should I solder to which post?

Thanks for all the help so far!
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hirollcenter



Joined: 19 Dec 2007
Posts: 5
Location: bluegrass

PostPosted: Fri Dec 21, 2007 6:58 am    Post subject: 13 in. tv Reply with quote

tip + ring or sleeve -...
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Fri Dec 21, 2007 9:47 am    Post subject: Reply with quote

JP in Wisconsin wrote:
Thanks for the tip.

If I put a voltmeter on those leads, what's a reading over which I'd need an isolation transformer?


You should not make this measurement across the leads, but from the internal ground of the tv to the ground pin of a grounded electrical outlet or any other "real ground".
When using a modern, high impedance multimeter, you will get a relatively high reading in all cases, but if the tv has isolation in its power supply, the reading will drop to a few volts if you put a resistor of some ten kiloohms across the multimeter.

Another way of figuring it out is to look at the PCB layout of the tv's power supply to see if there is a broad insulation barrier on the solder side of the PCB.
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JP in Wisconsin
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PostPosted: Fri Dec 21, 2007 2:29 pm    Post subject: Reply with quote

@hirollcenter - I believe it's tip and ring - one post is part of the outer sleeve, bent perpendicular to the direction you would insert a 3.5mm male end, and the other is attached to the interior of the jack and extends straight out the back of the jack.

@torbjorn - thanks for the added info.
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JP in Wisconsin
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PostPosted: Wed Dec 26, 2007 4:33 pm    Post subject: Reply with quote

I've got the TV apart and it looks like we're good on the current to the speaker - the back of the speaker has some info stamped on it, including a rating of 2.6 W. The wire leading to the speaker looks like 16 or 18 gauge copper stranded. I attempted the voltmeter reading, but the default on this TV is to mute the sound unless a signal is coming in - that means running some cable into my workshop to get a signal. Too much of a hassle, and the speaker info and wire size seem enough to convince me that there are very few volts running to the speaker.

I believe we are good to move forward.

But I'm still unsure of which wire to solder to which post on this 3.6mm jack. I know which the positive and negative leads are - I just need to know where to stick 'em.

Can anyone offer this last bit of advice? Thanks for all your help.
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