Since none of my other questions seemed to get answered about my project, perhaps I'll ask the questions a different way.
My project used ADC to measure water content in soil.
These rules/aims apply to the problem:
* 3.3v supply, max.
* Resistance of soil, is a range that falls between zero to several MOhm.
* The ADC pins must be grounded (Somehow) to stabilise the reading.
* Maximum accuracy within the desired range (unknown)
My first attempt based on the little I know about electronics was flawed (not so unexpectedly) - the readings from the ADC are all over the place because the ADC input pins are just floating, and the reference supply perhaps has some ripple as well, but that's another story.
Never the less, my current schematic (R6) looks something like the first image. With some browsing on the net, and the consequent discovery that the pins needed a path to ground to stabilise, comes the next revision (R7 - voltage divider), and finally third (R8) is one that's driving some model of NPN, with a source directly from the Vref.
Thoughts?
My project used ADC to measure water content in soil.
These rules/aims apply to the problem:
* 3.3v supply, max.
* Resistance of soil, is a range that falls between zero to several MOhm.
* The ADC pins must be grounded (Somehow) to stabilise the reading.
* Maximum accuracy within the desired range (unknown)
My first attempt based on the little I know about electronics was flawed (not so unexpectedly) - the readings from the ADC are all over the place because the ADC input pins are just floating, and the reference supply perhaps has some ripple as well, but that's another story.
Never the less, my current schematic (R6) looks something like the first image. With some browsing on the net, and the consequent discovery that the pins needed a path to ground to stabilise, comes the next revision (R7 - voltage divider), and finally third (R8) is one that's driving some model of NPN, with a source directly from the Vref.
Thoughts?
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