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Miceuz / i2c-moisture-sensor

I2C based soil moisture sensor
Apache License 2.0
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Attiny getCapacitance wrong? #7

Closed breemts closed 7 years ago

breemts commented 8 years ago

Hi, I wanted to "update" my sensor and see if it makes a difference. Now the capacitance reading is 1023-1025. I tried to figure out why and thats what I noticed. getCapacitance returns this: 1023 - (caph - capl) and on my sensor capl is higher than caph. So I wanted to know why. With my DMM I measured pin 6(PA7) wich should be capl, pin 8(PA5) should be caph and pin 5(PA2) wich isn't mentioned in the code but is connected to the sensor-traces. pin6 2.45V; pin8 2.46V; and pin5 2.43V. When I manipulate the code that I get capl and caph on my console capLow is alwasy 1-2 values higher than caphigh. capl values are 508-506 and caph values are 507-504. So I thought my Sensor is broken, but what part? I measured all components and they are all fine.

Than I took another sensor that I have and measured the Voltage on the pins. pin6 4.88V; pin8 4.94V; pin5 4.85V I get readings about 230 from this sensor.

So could it be that the code for the Attiny is wrong? When I do the calculation with the formal in the code and use the values of the working sensor I get this: 1023 -(991[4.94V] - 979[4.88V]) = 1011 So the working Sensor must have different code. And I think the Voltage difference is because PA2 the "Exitation" pin is not mentioned in the code. I think it should be set to "HIGH" or 1024, something like this.

Would be really nice if you could update your code. And what kind of IDE did you use for programming the Attiny? I'm uploading over a Arduino via ISP.

Best. Benjamin Reemts

madmax76 commented 7 years ago

And I think the Voltage difference is because PA2 the "Exitation" pin is not mentioned in the code. I think it should be set to "HIGH" or 1024, something like this.

Excitation is done by setting the CKOUT Fuse, see the Makefile. Did you check that? If I am not mistaken, the full 16MHz is put onto the sensor track via the 330Ohm resistor. I am currently investigating if it's possible to run without the external clock source (16MHz Crystal).

I have used both Atmel Studio as well as USBAsp with AVRdude to program the device.

Miceuz commented 7 years ago

I can guarantee that the code on the github is the same one I use to program sensors. It is possible to run on internal RC oscillator, but the main reason of adding a crystal was improved stability - internal oscillator drifts a lot with ambient temperature.