Thank you for your answer. Yes, obviously anything multiplied by zero equal zero...
Anyway, I tried several values for IN_STRAY_CAP_TO_GND, with no result. Displaying the mesured value (VAL) always shows 838, no matter what capacitor I test (or even with no capacitor at all). A0 tied to ground shows 0, and tied to VCC shows 1023, which seems correct. So appearently, measuring works. Maybe it's impossible to do with a 16F877A, but I doubt. Anyway, using the link you gave, I ordered some 18F45K22. Wait and see. For my application, I must take the measure this way, because the goal is to get a wire length "on the fly" when a default is detected on an analog input. A+ Gilles Le vendredi 31 janvier 2020 07:13:05 UTC+1, Kiste a écrit : > > const word IN_STRAY_CAP_TO_GND = 0 --initially this was 30.00 > const word IN_EXTRA_CAP_TO_GND = 0 > const word IN_CAP_TO_GND = IN_STRAY_CAP_TO_GND + IN_EXTRA_CAP_TO_GND > [...] > -- Calculate and print result > capacitance = (val * IN_CAP_TO_GND) / (MAX_ADC_VALUE - val) > > > IN_CAP_TO_GND is zero, therefore capacitance is always zero, no matter all > the other values. > > Using the not-so-well defined stray capacitance in a capacitive voltage > divider is of course possible, but there are PICs which have far better > peripherals built in for capatitance measurement. Take a look at > > https://www.microchip.com/maps/Microcontroller.aspx > > For "CPU Type" select "8-bit PIC MCU", then further down try "CTMU" > (Charge Time Measurement Unit) or "Capacitive Voltage Divider". > > Greets, > Kiste > > > Am Donnerstag, 30. Januar 2020, 23:30:47 MEZ hat Gilles BARTHELEMY < > [email protected] <javascript:>> Folgendes geschrieben: > > > Hello, > > I found this code for Arduino. It needs no additional part to measure a > capacitor value, just plug it between two pins of the microcontroller. > > const int OUT_PIN = A2; > const int IN_PIN = A0; > > //Capacitance between IN_PIN and Ground > //Stray capacitance is always present. Extra capacitance can be added to > //allow higher capacitance to be measured. > const float IN_STRAY_CAP_TO_GND = 24.48; //initially this was 30.00 > const float IN_EXTRA_CAP_TO_GND = 0.0; > const float IN_CAP_TO_GND = IN_STRAY_CAP_TO_GND + IN_EXTRA_CAP_TO_GND; > const int MAX_ADC_VALUE = 1023; > > void setup() > { > pinMode(OUT_PIN, OUTPUT); > //digitalWrite(OUT_PIN, LOW); //This is the default state for outputs > pinMode(IN_PIN, OUTPUT); > //digitalWrite(IN_PIN, LOW); > > Serial.begin(115200); > } > > void loop() > { > //Capacitor under test between OUT_PIN and IN_PIN > //Rising high edge on OUT_PIN > pinMode(IN_PIN, INPUT); > digitalWrite(OUT_PIN, HIGH); > int val = analogRead(IN_PIN); > > //Clear everything for next measurement > digitalWrite(OUT_PIN, LOW); > pinMode(IN_PIN, OUTPUT); > > //Calculate and print result > > float capacitance = (float)val * IN_CAP_TO_GND / (float)(MAX_ADC_VALUE - > val); > > Serial.print(F("Capacitance Value = ")); > Serial.print(capacitance, 3); > Serial.print(F(" pF (")); > Serial.print(val); > Serial.println(F(") ")); > > while (millis() % 500 != 0) > ; > } > > I translated it to Jal, I just adapted the pins to use, and converted > floating values to integer, since I don't need them for my application > > Include 16f877a > > Pragma Target CLOCK 20_000_000 > Pragma Target OSC hs > Pragma Target WDT disabled > Pragma Target BROWNOUT enabled > Pragma Target PWRTE disabled > Pragma Target LVP disabled > Pragma Target CPD disabled > Pragma Target WRT disabled > Pragma Target DEBUG disabled > Pragma Target CP disabled > > -- include delay > include print > include format > > -- Désactive les convertisseurs A/D > enable_digital_io() > -- > -- Mesure en haute résolution > const bit ADC_HIGH_RESOLUTION = high > -- On va utiliser un seul canal analogique > const byte ADC_NCHANNEL = 1 > -- Pas de tension de référence externe > const byte ADC_NVREF = ADC_NO_EXT_VREF > > include adc > adc_init() > > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > -- % Traitement du port RS232 > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > -- -- Définition des valeurs du port série > const USART_HW_Serial = TRUE -- TRUE = RS232, FALSE = SPI > const Serial_HW_Baudrate = 9600 > include Serial_Hardware > Serial_HW_Init > > -- some aliases so it is easy to change from serial hw to serial sw. > alias serial_write is serial_hw_write > alias serial_read is serial_hw_read > alias serial_data is serial_hw_data > alias serial_data_available is serial_hw_data_available > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > -- % FIN Traitement du port RS232 > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > print_cls_ansi(serial_data) > print_string(serial_data,"Debut programme\r\n") > print_crlf(serial_data) > > alias OUT_PIN is pin_B7 > alias OUT_PIN_DIRECTION is pin_B7_direction > alias IN_PIN is pin_A0 > alias IN_PIN_DIRECTION is pin_A0_direction > > --Capacitance between IN_PIN and Ground > --Stray capacitance is always present. Extra capacitance can be added to > --allow higher capacitance to be measured. > const word IN_STRAY_CAP_TO_GND = 0 --initially this was 30.00 > const word IN_EXTRA_CAP_TO_GND = 0 > const word IN_CAP_TO_GND = IN_STRAY_CAP_TO_GND + IN_EXTRA_CAP_TO_GND > const word MAX_ADC_VALUE = 1024 > > OUT_PIN_DIRECTION = OUTPUT > -- OUT_PIN = LOW --This is the default state for outputs > IN_PIN_DIRECTION = OUTPUT > -- IN_PIN = LOW > > var word val = 0 > var dword capacitance = 0 > > forever loop > -- Capacitor under test between OUT_PIN and IN_PIN > -- Rising high edge on OUT_PIN > IN_PIN_DIRECTION = INPUT > > OUT_PIN = HIGH > val = adc_read_high_res(0) > OUT_PIN = LOW > > -- Clear everything for next measurement > IN_PIN_DIRECTION = OUTPUT > > -- Calculate and print result > capacitance = (val * IN_CAP_TO_GND) / (MAX_ADC_VALUE - val) > > print_string(serial_data, "Capacitance Value = ") > print_dword_dec(serial_data, capacitance) > print_string(serial_data, " pF (") > print_word_dec(serial_data, val) > print_string(serial_data, ")\r\n") > > _usec_delay (1_000_000) > > end loop > > Unfortunately, it doesn't work at all, ADC doesn't see any change with > several values of capacitors, I can't figure out why... I obviously miss > something, but what? > Any idea will be welcomed! > > Link to the original project: > https://wordpress.codewrite.co.uk/pic/2014/01/21/cap-meter-with-arduino-uno/ > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/jallib/ad650a5f-d052-4470-a3c5-120156c01f3a%40googlegroups.com > > <https://groups.google.com/d/msgid/jallib/ad650a5f-d052-4470-a3c5-120156c01f3a%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "jallib" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. 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