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Topic: Analogue input impedance, crosstalk, sample-and-hold time (Read 861 times) previous topic - next topic

Jodes

Hi,

I need to sample several high-impedance circuits using the analogue pins (using the Arduino Nano).

Primary requirement is low component count and cost. Bandwidth requirements are very low. This means that I'm ruling out using op-amp buffers, etc.

According to this post, input impedance is about 100MOhm, but the charging of the sample-and-hold capacitor and multiplexing bring this down considerably, initially.

This begs the question, how can I programmatically work around this? In other words, is it possible to tell the microcontroller to switch the multiplex switch, sample and hold, wait a while, and then take a sample? How would I do that?

Thanks!



johnwasser

Read the same analog input multiple times and throw away all but the last sample.

Of course this assumes that your inputs change VERY slowly because the sample/hold capacitor is going to integrate the input over time.

From the datasheet:
"The ADC is optimized for analog signals with an output impedance of approximately 10 k? or less. If such a source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedance sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor."
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