[sdiy] Crosspoint Switch [was: Which programable chip?]

[Eric Brombaugh]

RTFM - from the circuit description on that page:

"How does a device (the 4051) that has only a 15v range allow at least 
+/-10V to pass through it? The answer is it doesn't. By powering the 
4051 and its associated drive circuitry from +14.4V and -0.6V, and 
placing the output of the analog switch at the virtual ground point of 
an inverting op-amp buffer, the full range of the signal is allowed to 
pass while the voltage at that point is held near or at 0V by the action 
of the op-amp while the analog switch is closed. When the analog switch 
is open, the diode connected between the input and 0V prevents in 
incoming signal from going below -0.6V, and thus prevents it from going 
outside the allowed input range. There is no need to protect against 
excursions in the positive direction, as these are in the allowed input 
range. A second diode at the output of the analog switch prevents the 
op-amp from driving the output below -0.6V, should the switch open while 
such potential exists. "

Eric

Ian Smith wrote:
> I'm not sure I'm seeing what you see Eric. I'm seeing the input still going through the 4051 and the output going to the opamp so the input still has to go through the 4051. Maybe I'm misunderstanding what you're saying.
> -Ian
> 
> ----------------------------------------
>> From: ebrombaugh1 at cox.net
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] Crosspoint Switch [was: Which programable chip?]
>> Date: Fri, 17 Apr 2009 07:37:39 -0700
>>
>>
>> On Apr 17, 2009, at 7:22 AM, Ian Smith wrote:
>>
>>>> Ummm....need to *carefully* check the voltage across the switch:
>>>> video is ~
>>>> 1.5V pk-pk Do NOT assume anything based on the supply voltages.
>>>>
>>>> Paul S.
>>> Bugger. In my defense I did this last night when I was half asleep.
>>> Well, either way it'll be interesting to see what I can pull out of
>>> the thing. Thank you for pointing that out.
>>> -Ian
>> Ken Stone's Sequential Switch design puts the analog switch/mux at the
>> summing node of an op-amp so that the voltage range of the switch
>> doesn't limit the overall range. Maybe you could use something like
>> that?
>>
>> http://www.cgs.synth.net/modules/cgs28_seq_switch.html