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Re: [AVR-Chat] Negative bias supply for signal conditioning op-amp

2005-03-31 by Mark Jordan

Have you tried the AVR analog comparator?

	Mark Jordan

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On 31 Mar 2005 at 11:49, Chuck Hackett wrote:

> 
> I'm using a 741 op-amp to condition an input signal.  It's setup like a
> threshold detector to detect a voltage level between .1 and .6 volts
> (adjustable).  It's my understanding (and experience) that the 741 can not
> operate that close to one of its rail voltages so I need to supply it with a
> negative rail voltage (I'm thinking -9v).  I have 12v supplied to the rest of
> the circuitry and need to avoid having a second supply (remote location).  I was
> thinking that I could generate -9v using a 555 timer, caps, R's and diode to
> rectify a negative voltage.  Can someone point me to a web site circuit for this
> using a minimum of components?  I assume I only need a very small current.
> 
> In the short term (this weekend) I need to stick with the 741 which I have on
> hand but can someone recommend an inexpensive "rail to rail" op-amp that would
> be better for my final configuration which would eliminate the need for the
> second supply?
> 
> Thanks in advance for any guidance you can give.  I'm mostly listening on this
> list but I'm learning a lot.  Thanks to all contributors for the resource.
> Someone on the list recommended "Embedded C Programming and the Atmel AVR" to
> someone else.  I ordered the book and read it in short order.  I found it very
> helpful in my "getting up to speed" <g>.
> 
> Regards,
> 
> Chuck Hackett
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>

RE: [AVR-Chat] Negative bias supply for signal conditioning op-amp

2005-03-31 by Chuck Hackett

> From: Mark Jordan [mailto:mark@cpovo.net]
> 
> 	Have you tried the AVR analog comparator?
> 
> 	Mark Jordan

Good thought but I'm doing field testing of a signal conditioner to be attached
to an AVR in the future but for testing this weekend there is no AVR available.
Also, there will be another stage of conditioning after the op-amp prior to the
signal being fed to the AVR.

In doing some web searching I have discovered:

http://ourworld.compuserve.com/homepages/Bill_Bowden/5volts.gif

and

http://www.northcountryradio.com/PDFs/column009.pdf

which would seem to cover the first part of my query.

Still would like low cost recommendations for a single supply op-amp that can be
used for inputs from .1 to .6 vdc.

BTW: Even though this will eventually feed an AVR is there another list of
helpful, non-flaming folks that I should direct questions like this to?  I
realized that it's not directly AVR related.  So far I just subscribe to lists,
haven't ventured into newsgroups yet.

Regards,

Chuck Hackett