At 10:04 PM 7/03/97 -0500, you wrote:
>>Thanks for this and I will certainly try this improved resolution. But with
>>the 16C71/74 I understand that the range input is that of the supply (5
>>volts) and so to get resolutions of 10 microvolts in 5 volts I need 20 bits.
>>If I could scale the range to read 0 to 200 millivolts then 16 bits is
>>enough. Alternatively I need 20 bits on an ADC.
>
>USE THE Vref PIN TO BRING YOUR REFERENCE DOWN!!!  You can go to 2.5V
>(Vcc/2, actually).  I've found best results with Vref < 3.0V.
>
>>This ADC/PIC/etc needs to be able to fit in a tube(with a pH probe,
>>conductivity probe and temperature sensor) which has external dimensions of
>>12mm diameter and 300mm long. This is why I require something small.
>
>Cool.  My brother was working as a waste treatment plant chemist for a
>while, and I did a model of their treatment system.  We had pH,
>conductivity, temp, and all kinds of other sensors in the system, and a PC
>to control it all.  He ended up with a neat gadget for measuring certain
>pollutants in a handheld size, but never marketed it.

It may not be too late. I think it is a pity that these very useful devices
sit idle on the shelf and they are re-invented every so often. He may like
to take a stab at marketing it. What does it do?

Thanks for the VREF solution. I missed this a sI was not considering the
16c71/74 as they are too larger for my application. I would like one of the
new PIC12C5XX series with the ADC built in but understand they will not be
available until sometime in April/May. I still may be able to use these.

Thanks again,


Peter
Neosystems