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Signal period and DC offset by ADC

 
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cucuruzel

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Joined: 18 Mar 2010
Posts: 52
Location: Cluj-Napoca

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PostPosted: Fri Mar 08, 2019 12:12 am    Post subject: Signal period and DC offset by ADC Reply with quote

Hi

I need to measure a triangular signal with a 10bit ADC and display the DC offset and Frequency (period).
The singnal is mostly symetrical, 5 to 100Hz, aprox. 2.5V DC offset and DC deviation needs to be measured.

I have made a simple simulator in Autoit to test the code that would be inside a 1ms timer interrupt, results in the screen capture.



This is some code (full script is attached, Autoit 3.3.14.2)

Code:
    For $i = 1 to $sim_samples

    ;----- signal generator -----
;               $adc=$gen_ampl*ASin(sin($i/$gen_period))+$gen_offset                                                                                                    ;TRIANGLE
                $adc=($gen_ampl/$gen_period) * ($gen_period - ABS(MOD($i, (2*$gen_period)) -$gen_period) )+$gen_offset  ;TRIANGLE2
;               $adc=($gen_ampl*sin(2*$pi*($i/100)))+$gen_offset                                                                                                                ;SINE

                $adc=$adc+Random(-$noise_ampl,$noise_ampl,1)    ;add random noise over signal

    ;----- signal capture an proccessing -----
        ;this would be in a 1ms timer interrupt (1Ks/s)
                $sig_period = $sig_period +1                                    ;count period ticks
                if $adc>$sig_max then $sig_max = $adc                   ;max peak detector
                if $adc<$sig_min then $sig_min = $adc                   ;min peak detector
                $sig_offset = (($sig_max-$sig_min)/2)+$sig_min  ;signal DC offset

                if $adc> $sig_offset then                                               ;detect "rising" signal
                        if $sig_dir=0 then                                                      ;signal was "falling" before
                                $sig_max=$adc                                                   ;reset maximum
                                $sig_avg_offset = ($sig_avg_offset + $sig_offset)/2     ;average DC offset
                                if $sig_trans_cnt= 2 then                               ;second transition, full period
                                        $avg_smin=($avg_smin+$sig_min)/2        ;average minimum
                                        $sig_avg_period=($sig_avg_period+$sig_period)/2         ;average signal period
                                        ConsoleWrite(@crlf & "! instant period : " & $sig_period & "  avg: " & $sig_avg_period)
                                        $sig_period=0                                           ;reset period counter
                                        $sig_trans_cnt=1                                        ;reset transition counter
                                        _GraphGDIPlus_Refresh($Graph)
                                endif
                        endif
                        $sig_dir = 1                                                            ;signal is "rising"
                endif
                if $adc< $sig_offset then                                               ;signal is "falling"
                        if $sig_dir=1 then                                                      ;signal was "raising" before
                                $sig_min=$adc                                                   ;reset minimum
                                $sig_avg_offset = ($sig_avg_offset + $sig_offset)/2 ;average DC offset
                                if $sig_trans_cnt= 1 then                               ;first transition
                                        $sig_trans_cnt=2                                        ;next transition
                                        $avg_smax=($avg_smax+$sig_max)/2        ;average maximum
                                        _GraphGDIPlus_Refresh($Graph)
                                endif
                        endif
                        $sig_dir = 0                                                            ;signal is "falling"
                endif
    ;----- draw graph -----

 


In short a min/max peak detector is implemented, the offset= ((max-min)/2 )+min, signal transitions are detected when signal intersects the offset and by counting two transitions in same direction a period is detected.

Is there a better way of doing this while keeping it low resource/simple ?

(BASCOM-AVR version : 2.0.8.1 )
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