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#This is enough code to read the output of a magnetometer and convert field strength readings into
#magnetic pole events. The sensor is mounted near a shaft that has 3 magnets attached to it with
#the sensor reading two north poles and one south pole per rotation. When a south pole is encountered
#it is considered a turn and the RPM of the shaft is calculated from the duration of the turn.
#With two north poles and one south pole it's possible to count the number of north poles detected
#and look at that value when the turn event is generated. If the count of the north poles is not two
#then some kind of error happened - it's possible to then reconstruct which pole was not counted
#Sample Output:
#Tyler@Tyler-PC ~/work/Firmdata
#$ perl portName com3 sessionFile
#Session started at Fri Aug 3 22:24:00 2012
#RPM is 122.581066945607 at line 99.
#RPM is 147.220477386935 at line 99.
#RPM is 160.97184065934 at line 99.
#RPM is 168.858069164266 at line 99.
#RPM is 174.386160714285 at line 99.
#RPM is 177.556818181819 at line 99.
#RPM is 180.288461538461 at line 99.
#RPM is 182.535046728972 at line 99.
#RPM is 183.10546875 at line 99.
package RPMController;
use Moose;
with 'Device::Firmdata::Role::Session';
has currentPole => ( is => 'rw', isa => 'Maybe[Str]', required => 1, default => undef );
has lastTurn => ( is => 'rw', isa => 'Maybe[Num]', required => 1, default => undef );
sub sessionOpen {
my ($self) = @_;
#connect output pin 1 and 2 to messages from channel 1 and 2
#args: pin, channel
#this is to send data to two servos
$self->publish(1, 1);
$self->publish(2, 2);
#connect input pin 1 to message channel 1; receive data at an interval of 2 timer ticks with
#zero phase offset
#args: pin, channel, interval, offset
#this is the magnetometer data and has to be sampled very quickly, 2 timer ticks gives a frequency of 1024hz
$self->subscribe(1, 1, 2, 0);
#connect input pin 2 to message channel 2; receive data at an interval of 100 timer ticks with a phase offset of 1 timer tick
#this reads the knob position around 204 hz; with the phase offset of 1 timer tick the sample will always be done at odd timer
#intervals and the magnetometer always happens at even ones - the sample requests will never colide with each other because
#a sample takes less time than a timer tick
$self->subscribe(2, 2, 100, 1);
sub sessionClose {
my ($self) = @_;
sub inputData {
my ($self, $channel, $when, $value) = @_;
if ($channel == 1) {
$self->got_magnetometer($when, $value);
} elsif ($channel == 2) {
$self->got_knob($when, $value);
#the magnetometer returns a value of 127 when there is no detected magnetic field
#the value moves towards 255 for a south pole and towards 0 for a north pole
sub got_magnetometer {
my ($self, $when, $value) = @_;
my $currentPole = $self->currentPole;
if (defined($currentPole)) {
if ($currentPole eq 's' && $value < 132) {
} elsif ($currentPole eq 'n' && $value > 125 ) {
#a single reading may both indicate that a pole is no longer present
#and that a new one has been detected so this should not be in an else
#block with the logic above that clears out the current pole
if ($value > 135) {
} elsif ($value < 122) {
sub inside_pole {
my ($self, $when) = @_;
#this is where north poles could be counted
#counting a turn when a pole is left instead of when it is entered
#solves the problem of the system starting when a pole is being
#read and that counting as a turn causing a false RPM value to be
#calculated even if the shaft is not turning
sub outside_pole {
my ($self, $when) = @_;
if ($self->currentPole eq 's') {
if (defined($self->lastTurn)) {
my $duration = $when - $self->lastTurn;
my $rpm = 1 / $duration * 60;
warn "RPM is $rpm";
sub got_knob {
my ($self, $when, $value) = @_;
warn "Knob at $when";
return "RPMController";
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