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Author Topic: Question On Optical Output ..  (Read 30 times)

majik655

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Question On Optical Output ..
« on: January 28, 2004, 06:58:00 AM »
As the subject states..

I tried getting a totx173 from digi-key.com and they state that part is no more and
the replacement part is a totx179

I see everywhere that a 100nF cap is needed over VCC and Ground..

then I read that a totx173 does not need a cap across the pins..  

so IF THIS IS TRUE??

Does the totx179 need it?

By the way why is the cap needed anyway?

Thanks!
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majik655

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Question On Optical Output ..
« Reply #1 on: January 28, 2004, 07:11:00 AM »
well I didn't see digi-key's online technical chat (which by the way is pretty cool)

they state totx179p DOES need a 100nF cap .

So I guess nevermind.

I still would like to know if the cap is needed ANY time you install a optical output.. say in a receiver that used to have rca digital?  (seems just need vcc 5v to be able to convert from rca digital to optical.)
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EvilWays

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Question On Optical Output ..
« Reply #2 on: January 28, 2004, 10:07:00 AM »
If you notice, there's three pins on the optical unit (data/input, vcc, and gnd). I assume the capacitor is there as a sort of regulator. The datasheet mentioned something about the LED being on when the voltage was high, and off when voltage was low. I could be wrong tho.
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majik655

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Question On Optical Output ..
« Reply #3 on: January 28, 2004, 10:10:00 AM »
I see.. Thank you .. I believe you are right.  

I was wondering if it was specific to what you were connecting it to.. meaning like different machines may need different connections.. (but probably not)

Thanks again!
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spillage

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Question On Optical Output ..
« Reply #4 on: January 29, 2004, 04:44:00 AM »
I think it is a decoupling capacitor.

Because of the nature of the connection, ie, data, the decoupling cap' will shunt or provide a low impedance path to ground. The cap goes between the supply (Vcc) and Ground (Gnd). Any trasient noise, blips and pulses etc will be grounded rather than affecting the integrity of the data.
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majik655

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Question On Optical Output ..
« Reply #5 on: January 29, 2004, 07:46:00 AM »
QUOTE (spillage @ Jan 29 2004, 06:44 AM)
I think it is a decoupling capacitor.

Because of the nature of the connection, ie, data, the decoupling cap' will shunt or provide a low impedance path to ground. The cap goes between the supply (Vcc) and Ground (Gnd). Any trasient noise, blips and pulses etc will be grounded rather than affecting the integrity of the data.

Ahh! now that sounds better!   Thank you
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