Re: SD24 to sample a resistive bridge with pulsed bridge supply

"Jon Kirwan [email protected] [msp430]" <[email protected]>:

> You can look up ideas with google using "sampled strain gauge
> signal conditioner" and see where that takes you. I'd avoid
> the sigma-delta for a pulse-powered bridge, though. But
> perhaps you can get enough experimental data from that one to
> see if you can make it work okay. I've never attempted it so
> I really don't have any experience to draw on, regarding real
> results. I just avoid them when I know I will be powering up
> and powering down an analog input system or using an analog
> input multiplexer. (They generally "don't like" switched
> inputs as it takes them time to "re-acquire" an input without
> mixing it up into a mush from the other states the input goes
> though.)

Jon, thank you for your idea's.  

Isn't it possible to just "pause" the sampling of the delta sigma converter 
(let it sleeping, all registers keep their values) and awake it after 100ms 
with nearly the same input level as before the sleep? The sd24_a input is
just a 18pF capacitor. The 350ohms will charge it quickly... 
Sure, I have to clock the adc as long as it is required to step the new 
reading completely through the full decimation filter.

The PIR example from texas instrument slaa283 is quite interesting,
It uses the sd16 to sample a big capacitor behind the PIR sensor. It is 
sampling the input for 1ms (4 samples each time) and sleep for 341ms. It 
seems interrupted sampling is possible with delta sigma too. 
To further reduce power consumtion they also switch the reference voltage 
off during sleep. It seems that the charge in the capacitor at the ref-pin 
will stay - accurate enough for this application - at ref-level for 341ms. 

https://www.olimex.com/Products/MSP430/Starter/MSP430-
PIR/resources/slaa283.pdf

Matthias



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Posted by: Matthias Weingart <[email protected]>
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