E+E Elektronik HCT01, Руководство разработчика

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Rev. 0.2 / 09 /2015 9
AN1111-2
All three measurement paths (“ sensor ” or “ reference ” or “ calibration ”) use the same
algorithm.
Example : reference path :
1.) Discharge all capacitors (I/O pins RC1, RC5, RC6, RC7 and RA2 = output LOW)
2.) Charge reference capacitor and C
L
(RC6, RC5, RA2 = input, RC1 = switched to
comparator input, RC7 = output HIGH). The charge from the reference capacitor
is also transferred in the capacitor C2 (=C
L
) and the voltage in C2 (=C
L
) rises a
little bit. C2 is approx. 10.000 times higher than C_REF.
3.) Discharging reference capacitor (RC6, RC5 = input, RC1 = switched to
comparator input, RA2, RC7 = output LOW).
4.) Increment the number of charge/discharge events (in this case N_C
Ref
).
5.) Check if the voltage at the pin RC1 (comparator) reaches the voltage at the
voltage divider:
no  repeat point 2.) and recharge the reference .
yes  end of loop and save the numbers of charge/discharge events.
6.) Each cycle measures the reference path and the sensor path and calculates the
sensor capacitance from these measurements.
3.1.1 Bill of Material
Quantity Symbol Device Dimension Supplier
1 pc HCT01 Humidity sensor HCT01-02 or HCT01-03 E+E Elektronik
1 pc D1 Fast Si-Diode 1SS400TiG
1 pc C2 Resistor 1 µF, ceramic / X7R
1 pc Existing
microcontroller
PIC16F690 Microchip
1 pc C_REF Capacitor 82 pF, ceramic / NP0 / CG0
5 pcs R1-R5 Resistor 470 Ω
Requirements for the microcontroller
1.) 3 to 4 digital I/O pins, switchable between output and (analog) input
2.) Integrated comparator (switchable to digital I/O output), external component also possible
3.) Integrated voltage divider (used as reference voltage at comparator), external component also
possible