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Miceuz / i2c-moisture-sensor

I2C based soil moisture sensor
Apache License 2.0
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Capacitive measurement #27

Closed rubengr closed 5 years ago

rubengr commented 5 years ago

Hi, I bought one chirp, and make another to test diferences.. I read from https://wemakethings.net/chirp/ that "chirp uses capacitive sensing to measure the moisture. 1MHz square wave (system clock is used for that) is output from the chip through a resistor into a big pad that together with the surrounding ground plane forms a parasitic capacitor. "

What i'm see in this code is just a diference between two readings. Can you explain how do you read the capacitance? 

uint16_t getCapacitance() {
    capMeasurementInProgress = 1;
    uint16_t caph = adcReadChannel(CHANNEL_CAPACITANCE_HIGH);
    uint16_t capl = adcReadChannel(CHANNEL_CAPACITANCE_LOW);
    capMeasurementInProgress = 0;
    return 1023 - (caph - capl);
}

Thanks

Miceuz commented 5 years ago

I am reading the capacitance the same way as described, but the idea is extended a bit further. I am measuring both peak and dip levels of the resulting triangle wave, capacitance estimate is a difference of those two numbers. Note, I don't return a true capacitance value in Farrads, just an arbitrary number that changes with changing capacitance.

rubengr commented 5 years ago

How do you know in microcontroller if we are on peak or dip level?