I have tried that circuit without the "BFTranzorb" and the 2k resistor with 
the same noisy results.
I guess I live a sheltered life, this was the first time I had heard the 
word "Tranzorb"

John Ferrell    W8CCW

"All that is necessary for the triumph of evil is for good men to do 
nothing." -- Edmund Burke
http://DixieNC.US

----- Original Message ----- 
From: "Spehro Pefhany" <speff@interlog.com>
To: <piclist@mit.edu>
Sent: Wednesday, May 07, 2008 11:58 AM
Subject: Re: [PIC]Analog signal conditioning


> Quoting "M. Adam Davis" <stienman@gmail.com>:
>
>> Something you might try is measuring using current from the shack
>> side.  Set up a constant current source (LM317 or similar) and then
>> measure the voltage at the output of the regulator.  The voltage will
>> vary based on the position of the pot in order to make the current
>> constant.
>>
>> It should help significantly, based on the description of the problems
>> you're having.
>>
>> -Adam
>
>
>
>
>     Vdd
>    +----------+
>              .-.
>              | | 499R
>              | |
>              '-'
>               |
>               +------------+--------------------------------+----+
>                            |                                |    |
>             \ |            |                               .-.   |
>               -            |                     500R Pot  | |<--+
>    BFTranzorb ^ \          |                               | |
>    eg. 10V    |            |                               '-'
>               |            |                                |
>     +---------+----------- | -------------------------------+
>               |            |
>              ===           |
>              GND           |
>                            |
>                            |
>                            |
>                            |
>                            |                      To ANx PIC
>                           .-.     +------+---------------+
>                        2K | |     |      | +
>                           | |     |     ---
>                           '-'     |     ---  47uF/16V
>                            |      |      |
>                            +------+      |
>                                         ===
>                                         GND
>
>
> The voltage at the ADC input is
>
> V = Rx/(499 + Rx) so it varies from 0 to about 2.5V for pot value from
> min to max (ignoring wire resistance etc.)
>
> It's a trivial exercise to solve for Rx as a function of ADC reading.
>
> Best regards,
> Spehro Pefhany
> -- 
> "it's the network..."                          "The Journey is the reward"
> s...@interlog.com             Info for manufacturers: 
> http://www.trexon.com
> Embedded software/hardware/analog  Info for designers: 
> http://www.speff.com
>
>
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
> 


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist