YHDC current sensor - the theory please

[richard]

a simple digital peak detector will give a reasonable result,

eg
2v p-p input offset to approx 1.5v for a vcc of 3.3v for adc




[arduino ide serial plotter]
at a 200us sample rate


at 1000us sample rate , its still not bad

'****************************************************************'*  Name    : peak_detector_ADC_16F18446.pbp
'*  Author  : richard
'*  Notice  : 
'*          : All Rights Reserved
'*  Date    : 
'*  Version : 1.0
'*  Notes   :








 '====== PIC 16F18446 FUSES ========================================================================
  #CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_ON & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTS_PWRT_64 & _LPBOREN_OFF & _BOREN_SBOREN & _BORV_LO & _ZCDDIS_OFF & _PPS1WAY_OFF & _STVREN_ON
    __config _CONFIG3, _WDTCPS_WDTCPS_31 & _WDTE_SWDTEN & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _BBSIZE_BB512 & _BBEN_OFF & _SAFEN_OFF & _WRTAPP_OFF & _WRTB_OFF & _WRTC_OFF & _WRTD_OFF & _WRTSAF_OFF & _LVP_OFF
    __config _CONFIG5, _CP_OFF
  #ENDCONFIG 


' ====== REGISTERS =================================================================================


    ANSELA  = % 00100000
    ANSELC  = % 00000000
    TRISC   = % 11101111
    ADCON0  = % 10000100 'ADC is ON, RIGHT justified result 


' ====== DEFINES ===================================================================================
    DEFINE OSC 32
    DEFINE ADC_BITS 12     'Number of bits in ADCIN result
    DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
    DEFINE HSER_CLROERR 1 ' Clear overflow automatically
    'DEFINE HSER_SPBRG 138 ' 57600 Baud @ 32MHz, -0.08%
    DEFINE HSER_SPBRG 68  ' 115200 Baud @ 32MHz, 0.64%
    SP1BRGH = 0
    BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
    pause 500
    RC3PPS = 15          ;tx            PORTC.3 
    RA0PPS = 15          ;tx            PORTA.0      ;PK3
    RC4PPS = 0           ;rx            unused
    LED    VAR LATC.4
    clear
    new_read     var word
    State        Var BYTE 'serial Bd (baud per second)
    peak         var word
    last         var word


' ====== setup PROGRAM =============================================================================
    led = 1
    ADCIN 5, last  
    pause 1000
    HSEROUT ["ready ",13,10]
    led = 0    
     ;707 -3670
' ====== MAIN PROGRAM =============================================================================
MAIN:
    ADCIN 5, new_read ' ADC 
    gosub getpeak
    HSerout ["ADC:",dEC new_read,",peak:",dEC peak,13,10]                    '    PLOTTER
    pauseus 200   ;   sample rate                         
GOTO MAIN


getpeak:
    if state==0 then    ;rising
       if   new_read < last  then
        state = 1;falling 
        peak =   last
       endif
    else        ;falling
       if   new_read > last   then 
        state = 0;rising 
        peak =   last
       endif
    ENDif
    last = new_read
return

[flotulopex]

Peak detector! That's it!

Thanks a lot for explaining and the code I can't wait to try when I'm back from office

Though, why do I always read about 3.3V measuring circuits and not 5V?

Also, a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?

If "yes", how do I dimension them? Are trials and readouts on the scope the best way to go?

[richard]

why do I always read about 3.3V measuring circuits and not 5V?

my dev board has a 3.3v reg, otherwise can't see that it makes a difference

a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?

not really , it needs a rectifier too. if the wave is not symmetrical the neg and pos peaks may be needed. plus it still needs adc code to read it in anyway

Are trials and readouts on the scope the best way to go?

almost essential, especially depending on the nature of the current being monitored,
if the current is not sinusoidal and/or varies rapidly then its going to need filtering and other compensation to get any sort of reasonable calibration

[flotulopex]

a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?
not really , it needs a rectifier too. if the wave is not symmetrical the neg and pos peaks may be needed. plus it still needs adc code to read it in anyway

May I kindly ask for a principle circuit to start with the correct foot please?

I don't see how to "rectify" a very low AC signal - I'm an electrician and used to easely handle voltages over 230VAC but when it comes down to millivolts.... 😬

[richard]

Why do want a nasty old analogue peak detector, When you can create a digital one as per my code ?
Using the very cct you posted.
If you realy need to try analogue google ""peak detector circuit"



An accurate analogue peak detector uses an opamp to create an "ideal" diode [overcome the diodes vf ]

[flotulopex]

...sorry Richard, didn't try your code by now - still in office.... 😬

[flotulopex]

Richard,

I've connected my YHDC sensor one pin to ground and the other to RA5. Got readings (see hereunder).

Because I'm not sure what I'm doing right now with the current sensor, I tried to add a 1Mohms resistor and a 100nF polarized cap between GND and RA5. Same readings.

Just for info, my multimeter shows 0.157mVAC - I'm measuring a 230VAC 42W light bulb for now.

I get readings on my serial monitor but the values don't make too much sense to me, for now - there's going to be some kinf of scaling to do, no?


This is what I get for now with bulb "ON":



And bulb "OFF":