Interfacing MSP430 to analog AC-rated humitidy resistive sensor HCZ-H8

Posted on Feb 5, 2014

Hmmm, if it is resistive, AC is equivalent to pulsed DC and the sensor is degraded in any case with the RMS value of the AC signal. If you appy 1VAC RMS, you could as well apply 1V DC. If you use an ADC10 or ADC12, the samples are take one after another (also for most devices with an SD16, only the devices for energy metering support simultaneous

Interfacing MSP430 to analog AC-rated humitidy resistive sensor HCZ-H8
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sampling). And if you`re already samling one after another and have to calculate the time shift, you can as well just sample the result, as it was you who created the input signal with the DAC, so you KNOW the input voltage (calibration provided). For resistive sensors, however, I would go a different approach: set up a small constant current source that can be switched on and off by an MSP port pin. Every millisecond switch it on, take a sample of the resulting voltage across the sensor, then switch it off again, to avoid sensor heating. if your current source forces 1mA through the sensor and the voltage reading is 1V then the sensor resistance is 1kOhm. I guess the calibration table takes the sensor heating caused by the measuring voltage into account. but only for a given environment temperature. To simulate it, calculate the power applied to the sensor under the the conditions of the calibration table, and apply a constant current that causes the same power loss on the sensor. The readings should be equal. Then the current source does not need to be switche on and off (except to save power, but then the first readings after turnign it on again will be inaccurate) and things are even easier: read teh voltage and convert it into a temperature by a table. Before posting bug reports or ask for help, do at least quick scan over this article. It applies to any kind of problem reporting. On any forum. And/or look here. If you...

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