AVR-Chat

1. See figure 5, AN11 at www.linear.com for one way to generate 
negative bias.

2. Maxim semi offers switched cap bias supplies that even have low 
noise and adjustable regulation output... see this 
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1205/ln/

Al Welch


--- In AVR-Chat@yahoogroups.com, "Chuck Hackett" <egroupscdh@W...> 
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