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Old 18th December 2002, 01:21 PM   #21
Rarkov is offline Rarkov  England
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I challenge anyone to solder a BGA chip with a soldering iron alone (+ solder )...

Good luck!

As I see it, as long as you have a solder barrier (or whatever they're called) between the pads of the chip, you can just run your iron along them with no bridging...
Gone are the days of having an iron in one hand and a scalpel in the other!

Gaz
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Old 18th December 2002, 04:24 PM   #22
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I think im just gonna go the expensive route and use 2 radioshack TV transmitter things, as i cant find any other reliable radio transmitters. Do you think a higher quality wireless phone radio could be used? it would probably be a much cheaper alternative, and range isnt all too important, but im thinking that a phone just wouldnt have enough bandwidth for digital music, dont phone systems only use a very limited range of the freq band? i guess if a signal is digital, the only requirement would be that the frequency of the radio is above the switching frequency of the digital signal, so maybe this would work; does anyone know what logic levels are standard for digital audio equipment? 5v? less? i wonder if a phone radio could handle 5v, or if it couldnt you could just put a resistor on the sending end, and an opamp on the recieving end to lower then restore valid logic levels. any suggestions? one more stupid question, the digital amp im planning on using says it needs a PWM signal input, is this analagous to a PCM signal?
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Old 18th December 2002, 04:35 PM   #23
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I made some wireless headphones (and microphone, since the parts were already there...) out of a pair of phones once, and the quality wasn't that great. Granted, these weren't top of the line phones that I pulled apart, but if you're using top of the line phone parts, you may not save any money by going that route.
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Old 19th December 2002, 09:17 AM   #24
Rarkov is offline Rarkov  England
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PCM is not even close to PWM...It is a common mistake.
Pulse Code Modulation is something I'm not totally familiar with - but you cannot recreate audio without a digital interface IC...

PWM I know alot about! It stands for Pulse Width Modulation. The Period is fixed (at least in most systems - except the modern ones)...As the amplitude of the input signal rises, the pulses of the 'on' state get wider, therefore the 'off' state pulse gets proportionally shorter. When it decreases to maximum amplitude on the negative side, the same happens, except it is the 'off' pulses that get wider.

You can then amplify this using a transistor/MOSFET setup as a digital switch, hence the v. high efficency.

Here comes the useful bit...
Using a Low Pass Filter recreates the input signal by taking an 'average' of the PWM...Obviously, when the 'on' pulses are wide, the average is high, and vice versa. After the LPF, a simple DC blocking capacitor will take out the inherant DC...

So from that fairly long explaination, PWM can be recreated into analogue using a passive LPF whereas PCM cannot. BTW, it certainly is not a stupid question - many people who should know better ask the same thing!

Hope this helps a bit...
Gaz
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Old 19th December 2002, 09:49 AM   #25
dhaen is offline dhaen  Europe
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Default TV transmitters

Any do'able system will require twice the bandwidth for digital: Nyquist.
Banwidth is a real problem. The license free modules to the best of my knowledge are going to limit you too much.
Yoda's TV repeater seems the best idea to date:
You could produce 4 or more subcarriers: Eg 100KHz, 200KHz, 300KHz, 400KHz, (best not to be harmonically related), and FM modulate them. Then add them to the baseband (video input) of the TV transmitter. Use a TV repaeter receiver at each speaker, and pick off the individual carrier, and demodulate.
There is plenty of bandwidth (at least 4MHz) for a digital system if you want, but it's adding complexity, and you must then think about error correction.
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Old 19th December 2002, 04:21 PM   #26
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Quote:
Originally posted by Rarkov
PCM is not even close to PWM...It is a common mistake.
Pulse Code Modulation is something I'm not totally familiar with - but you cannot recreate audio without a digital interface IC...

Gaz

Thatís right. To get PCM you have to
Sample the analogue signal in periodic intervals; this will get you a PAM signal.

You quantify the amplitudes of the samples. The signal is still PAM. But I guess you could look at it as a digital signal since it is quantified, both in time and amplitude making them discrete bundles of energy.

Then you convert the amplitudes to n-bit word. Voila you got yourself a PCM signal. Which as you already mentioned needs to be decoded (usually to PWM and thru a filter) if the speaker is to understand what the signal is saying

Please do correct me if I'm wrong!

Anyway itís an interesting project and I guess the first thing you would have to decide is how to transmit the signal thru the ether (or another possible way that I canít see anybody has mentioned is sending the signal thru the power line

If you decide to go with the AM or FM (FM being preferable I think) Iíd use AM respectively FM modulation. If you go thru Bluetooth or some other digital concept I would encode the signal digitally and then convert them back at the speakers. In that case I donít see a need to send the signals as PWM since you still have to convert the signal to a digital one (ie analogue-digital-PWM instead of (analogue-PWM-digital-PWM) Incidentally if you use Bluetooth there are many that are made with build in functions for audio transmit (both CD and phone quality sound). These also incorporates many function such as volume control etc although Iíve have only seen surface mounted Bluetooth transceivers).

I can see that Iím beginning to rant at this point. I might rant some more later when I remember what you asked for Good luck and let us know how the project is proceeding!

Mike
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Old 19th December 2002, 07:02 PM   #27
Rarkov is offline Rarkov  England
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I would prefer to transmit in Digital...Even if it's ASK, FSK or PSK modulations. The best modulation for digital that I can think of is PWM though. My only concern is timing and whether it'd get out of sync. Maybe if the picked up two tranmissions. A clock and the channel's data. Or maybe we could create a new type of modulation...a kind of cross between PWM and Manchester coding so the clock is in the data...

The reason I thought PWM is a good idea is that it is modulated by means of amplitude so that volume is inherantly coded into the data...
Gaz
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Old 19th December 2002, 07:06 PM   #28
dhaen is offline dhaen  Europe
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If you used a video sender, - (ha, you can tell what MY preferred option is), then you could either frequency multiplex, or time multiplex.
But you have to plan what happens if there is interference or a break in data.
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