[sdiy] Re: Inexpensive 16 bit DAC?

[Ray Wilson]

Yes for a simple A to D convertor the switches are overkill but... wait 
there's more. You could apply an AC signal that was oscillating about vdd/2 
and this would now act like a digital attenuator. So see there was method to 
my madness. Also the switches allow you to adjust the highest voltage output 
by connecting all of the inputs to a regulated voltage lower than the vdd.

But I admit your observation is correct about the simple A to D convertor. 
(my face is a little red).

Ray



----- Original Message ----- 
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, April 28, 2005 8:22 AM
Subject: Re: [sdiy] Re: Inexpensive 16 bit DAC?


> It seems to me that the analog switches are overkill and could be replaced 
> by
> a CMOS inverter gate (or buffer) per bit.  It looks to me that the 
> switches
> are simply providing a solid 12 volts or a solid ground to one end of each
> resistor.  I'm really not sure why a 4069UB  wouldn't work as well at less
> than half the part count.  Ok, you would want to do TTL to CMOS level
> conversion, but still it would be fewer parts.  A 4066 is a bidirectional
> device but you are using it as a unidirectional device which is why I 
> think a
> 4069UB design would work just as well.  The 4069 would be powered from +12
> and ground, the output of each gate hits the resistor.  If the whole thing
> were powered by +5 and ground, it would be even simpler.
>
> Is there some advantage the 4066 provides that I'm not seeing?
>
> "Ray Wilson" <raywilson at comcast.net> wrote:
>>
>>Here is a DAC with CD40106 and CD4066 chips. I have demo'd 4 bits but you
>>could go as many as you had patience to build.
>>
>>Ray
>>
>>----- Original Message ----- 
>>From: "KA4HJH" <ka4hjh at gte.net>
>>To: "Bob Weigel" <sounddoctorin at imt.net>
>>Cc: <synth-diy at dropmix.xs4all.nl>
>>Sent: Wednesday, April 27, 2005 3:24 AM
>>Subject: Re: [sdiy] Re: Inexpensive 16 bit DAC?
>>
>>
>>> >Usually you have to tell them that you are like working on something
>>>>where you might actually BUY some chips to get samples...or does Analog
>>>>just hand them out to anyone?  I could have been getting samples all
>>>>along for the project I'm working on from microchip but I haven't even
>>>>had time to ask for them and I feel bad doing it because we really don't
>>>>need them except that that company is out of money I guess so maybe we
>>>>do :-). -Bob
>>>
>>> They may ask you a few simple questions, like "What's this for?" or
>>> "What's
>>> the goal of the project?". So you just answer "experimental interface
>>> design for musical instrument" or something lofty you've daydreamed 
>>> about
>>> but will probably never get around to. Talk like a junior in 
>>> college--half
>>> clueless but you know some buzzwords.
>>>
>>> Maxim is another one you want to hit up...they've got good stuff...
>>>
>>> -- 
>>>
>>> Terry Bowman, KA4HJH
>>> "The Mac Doctor"
>>>
>>> "You'd PAY to know what you REALLY think"--Dobbs
>>
>>
>
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