Bill Of Material - E+E Elektronik HCT01 Developer's Manual

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
comparator input, RC7 = output HIGH). The charge from the reference capacitor
is also transferred in the capacitor C2 (=C
little bit. C2 is approx. 10.000 times higher than C_REF.
3.) Discharging reference
comparator input, RA2, RC7 = output LOW).
4.) Increment the number of charge/discharge events (in this case N_C
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
sensor capacitance from these measurements.

3.1.1 Bill of Material

Quantity Symbol
1 pc HCT01
1 pc D1
1 pc C2
1 pc
1 pc C_REF
5 pcs R1-R5
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
Rev. 0.2 / 09 /2015
capacitor and C
(RC6, RC5, RA2 = input, RC1 = switched to
L
L
capacitor (RC6, RC5 = input, RC1 = switched to
reference path and the
Device Dimension
Humidity sensor HCT01-02 or HCT01-03
Fast Si-Diode 1SS400TiG
Resistor 1 µF, ceramic / X7R
Existing PIC16F690
microcontroller
Capacitor 82 pF, ceramic / NP0 / CG0
Resistor 470 Ω
) and the voltage in C2 (=C
Ref
sensor path and calculates the
AN1111-2
) rises a
L
).
Supplier
E+E Elektronik
Microchip
9