Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!sumax!amc-gw!richm
From: richm@amc-gw.amc.com (Rich Moran)
Newsgroups: sci.electronics
Subject: Re: Audio Signal Conversion
Message-ID: <1166@amc-gw.amc.com>
Date: 19 Mar 90 19:29:12 GMT
References: <22500.260029fb@kuhub.cc.ukans.edu>
Reply-To: richm@the-end.amc.com (Rich Moran)
Organization: Applied Microsystems, Redmond, WA
Lines: 79

In article <22500.260029fb@kuhub.cc.ukans.edu> whitten@kuhub.cc.ukans.edu writes:
>
>Could anyone tell me what the most efficient way to convert +1 to -1
>audio signals to 0 to +5 volts?  The analog to digital IC I'm using
>will only work on zero to five, and everything I've tried so far has
>had pretty crummy results. (Lots of noise and the likes.)
> 
>Thanks,
>Chris
>
>Chris Whittenburg
>University of Kansas
>WHITTEN@KUHUB.CC.UKANS.EDU


        +5V
        _
        |
        >
        >10K
  1uF + >       |\
   -||--o       |  \    U1a
   |    > VR1   |    \
   |    ><------|+     \
   |    >       |        \             + 10uF
   |    |       |         >------o-------||--i
   |    |       |        /       |           |
   |    |     --|-     /         |           |
   |    >     | |    /           |           V
   |    >10K  | |  /             |          gnd
   |    >     | |/               |
   |----o     |                  |
        |     !-------------o----o
        V                   |    |
        gnd                 |    |
                            |    >
                            |    > 620
                            |    >       |\    U1b
                10uF N.P.   |    |       |  \
     Sig in >----||--------------o-------|+   \
                            |            |      \
                            |            |        \
                            >            |         >-------o-------->> Sig out
                            >10K         |        /        |
                            >            |      /          |
                            |    --------|-   /            >
                            |    |       |  /              >50k
                            |    |       |/                >
                            |    v                         |
                            ---^^^^-------------------------
                               VR2



Here's something to try. This assumes that you only have the single +5V
supply available.

U1 is a reasonable quality multiple op amp capable of swinging its output
to the 0 and 5-volt rails (i.e., CMOS; eg., National LMC660).

U1a provides a 1/2 VCC reference by dividing the +5V input.  This reference
should be adjusted to precisely 1/2 VCC using 1K-ohm potentiometer VR1.

The input signal is coupled through a non-polarized capacitor, and referenced
to the 1/2VCC rail via a 620-ohm resistor (note that this gives you a ~620-ohm
input impedance).

U1b is a non-inverting amplifier with a gain of approximately 5, again
referenced to the 1/2VCC rail.  A gain of 5 allows a typical 1V pk-pk
audio line-level signal to be adjusted to the 0-5V range.  The gain of
this stage can be precisely adjusted using 5k-ohm potentiometer VR2.
                           
Rich

-- 
=============================================
Rich Moran
richm@amc.com
=============================================