Russell,

On Sun, 15 Jan 2006 18:51:55 +1300, Russell McMahon wrote:

> Back from holiday ....

Welcome back!  It's been quiet around these parts.  Too quiet...

> 3000+ photos later ... :-)

Will you be publishing?

I have learned a lot from your messages on this topic (I'd always assumed that "saturated" was pretty-much a 
single constant state, and it never occurred to me that there could be such a change in Vce).

However, this:

> (10:1 = 3.32 BITS FWIW).

 is one of the daftest things I've seen you write!  :-)

> My first attempt used a single floating transistor but this (stupidly) 
> included the base drive in the lower divider resistor. Usually that's 
> reasonably irrelevant. Here it's fatal. So I now have two transistors 
> in a classic bipolar high side drive.

Are you going to publish the circuit, for those of us lacking in classical education?  :-)  To my rather 
simplistic understanding, Gain (Beta) is Collector current / Base current.  To get this < 1, Ic must be less 
than Ib.  Where does the "extra" Base current go?  (I was never any good at transistor electronics - digital 
is my thing :-)

> * Increasing input impedance first affects the dynamic response due to 
> time constant effects and these are not overly crucial here, but still 
> higher values impact accuracy due to bias currents.

Is significant settling time needed between turning on the divider and measuring the voltage?  (You don't 
actually say you're measuring battery voltage, but this sort-of falls out from the fact that you're connecting 
it to an ADC).

Cheers,


Howard Winter
St.Albans, England


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