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

Name: RigolDS0.jpg Views: 179 Size: 160.1 KB


[arduino ide serial plotter]
at a 200us sample rate
Name: peak200.jpg Views: 191 Size: 107.3 KB

at 1000us sample rate , its still not bad
Name: peak1000.jpg Views: 187 Size: 139.7 KB


Code:
'****************************************************************'*  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