Re: 6569 luminances

From: Segher Boessenkool <*segher_at_kernel.crashing.org*> Date: Tue, 15 May 2012 11:38:49 +0200 Message-Id: <D7504C1B-D96B-4CE7-B6EE-1FB3462F69EA@kernel.crashing.org> · segher_at_kernel.crashing.org

>> Curiously, the "middle" voltage for the audio ("analog ground"
>> if you will, +4.5V) is generated from +5V, not +9V. I wonder
>> why that is.

[It's 4.75V, not 4.5V; seems I cannot even get a resistor
divider right.]

> Maybe because +5V is already very close to what was needed?

Yeah, probably.  This way, the maximum deviation from the 4.75V
voltage (due to mismatches in the resistors) is smaller than if
it was derived from 9V.

Here's the circuit, esp. useful if you want to laugh at how I got
to 4.5V ;-)

Segher

       +5V
   ____________
     |      |
     |      X
     |      X 1R
     |      X
     X      |
10R X      +------ out
     X      |
     |      X
     |      X 4R
     |      X
     |      |
     +------+
     |
     X
10R X
     X
     |
    ===

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