calculate rms using sox on 1s audio snippets

[air-quality] / zph02.pl

diff --git a/zph02.pl b/zph02.pl
index 50aadcb..d0797d9 100755 (executable)
--- a/zph02.pl
+++ b/zph02.pl
@@ -3,6 +3,7 @@ use warnings;
 use strict;
 # sudo apt install libdevice-serialport-perl libdata-dump-perl
 use Device::SerialPort;
+use Time::HiRes;
 use Data::Dump qw(dump);
 
 my $port = shift @ARGV || '/dev/ttyUSB0';
@@ -22,12 +23,24 @@ $s->read_const_time(10);
 while (1) {
 
        my ($len, $string) = $s->read(9);
+       my $t = int( Time::HiRes::time() * 1_000_000_000 );
+       die $! if ! defined($len);
        if ( $len > 0 ) {
                my @v = unpack('C*', $string);
-               warn "# $len ",dump($string), dump( @v ), $/;
+               #warn "# $len ",dump($string), dump( @v ), $/;
+
+               my $sum = 0;
+               # -2 is specified in datasheet, next byte is 0 so it's same as -1
+               foreach my $i ( 0 .. $#v - 2 ) {
+                       $sum += $v[$i];
+                       $sum = $sum & 0xff;
+               }
+               $sum = ~$sum & 0xff;
+
+               my $checksum = $v[8];
                my $pcnt = $v[3] + ( $v[4] / 100 );
-               if ( $v[0] == 0xff ) {
-                       my $influx = "zph02,dc=trnjanska pm25_pcnt=$pcnt";
+               if ( $v[0] == 0xff && $sum == $checksum ) {
+                       my $influx = "zph02,dc=trnjanska pm25_pcnt=$pcnt $t";
                        print "$influx\n";
                        system "curl --silent -XPOST '$influx_url' --data-binary '$influx'"
                }