check checksum before sending data to influx

diff --git a/zph02.pl b/zph02.pl
index 50aadcb..4233660 100755 (executable)
--- a/zph02.pl
+++ b/zph02.pl
@@ -24,9 +24,19 @@ while (1) {
        my ($len, $string) = $s->read(9);
        if ( $len > 0 ) {
                my @v = unpack('C*', $string);
        my ($len, $string) = $s->read(9);
        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 );
                my $pcnt = $v[3] + ( $v[4] / 100 );

-               if ( $v[0] == 0xff ) {
+               if ( $v[0] == 0xff && $sum == $checksum ) {

                        my $influx = "zph02,dc=trnjanska pm25_pcnt=$pcnt";
                        print "$influx\n";
                        system "curl --silent -XPOST '$influx_url' --data-binary '$influx'"
                        my $influx = "zph02,dc=trnjanska pm25_pcnt=$pcnt";
                        print "$influx\n";
                        system "curl --silent -XPOST '$influx_url' --data-binary '$influx'"