>Brent Brown wrote:-
<snip>
>Can I minimise the electronics by putting the outputs of the four
>strain gauge bridges in parallel (maybe with some series resistors)
>and then just use one bridge amplifier and one ADC input on my
>micro? (Rather than 4 x bridge amps, 4 x ADC's)

Urk! don't do it! accurately measuring strain gages is hard enough
without introducing additional errors.

You don't need another 4 adc's All you need is a 4 channel differential
mux. If you can add another two channels you can do auto-zero and
auto-calibration. Hard wire one channel to analog ground, and hard
wire a suitable stable reference voltage say 10mv or so to another
channel. So for this approach you need 6 channel differential. You
could get 8 channels using 2x 4051's and measure something else with
your two spare channels.


<snip>
>Also, what are your favourite bridge amplifier's for a job like this?

Take a look at the Linear Tech LT1101. It has good temperature stability
and very high input impedance and linearity. Also check out the Burr Brown
INA2128. Take care to use single point ground for all your analog
circuitry.

You might want to consider VtoF rather than an ADC and use the PIC
to measure the frequency. This approach can give you higher resolution
and tends to cancel short term fluctuations, the downside is it will
be slower. The final choice depends on what you are trying to measure
and how fast.


Ray Gardiner ray@dsp.com.au