This wasn’t quite what I wanted and the playTone function expects the notes and timing to be in global variables which makes the baby jesus cry. The premise was simple though. Take the period and divide by two then bring the output high then low for this amount of time, repeat to make up the desired duration.

int pinSpeaker = 10;

void setup () {
    pinMode(pinSpeaker, OUTPUT);
}

void loop () {
    playTone(750, 500);
    delay(750);
}

// duration in mSecs, frequency in hertz
void playTone(long duration, int freq) {
    duration *= 1000;
    int period = (1.0 / freq) * 1000000;
    long elapsed_time = 0;
    while (elapsed_time < duration) {
        digitalWrite(pinSpeaker,HIGH);
        delayMicroseconds(period / 2);
        digitalWrite(pinSpeaker, LOW);
        delayMicroseconds(period / 2);
        elapsed_time += (period);
    }
}

This simple sketch plays a 500Hz tone for 750 mSec, pauses 750 mSec and repeats. To use it in your sketch simply define pinSpeaker and set it for output, copy playTone to your sketch and call it with the duration in milliseconds and the frequency in hertz.

The output:

Reading my RSS feeds before bed, I found “My new ticket tracking system is now vaporware” from Matt Wilson’s blog talking about Pitz, his soon to exist Python implementation of Ditz.

Please take a few moments to read over the feature set and example commands on the Pitz site and let Matt know about any ideas/suggestions you may have.

[michael@orion(~/)] perl -MPOE::Filter -e 'print $POE::Filter::VERSION, "\n"'
1.2357

So I added a quick function to .bashrc:

pm-vers () {
    perl -M$1 -e "print \$$1::VERSION, \"\n\""
}

Now I just run:

[michael@orion(~/)] pm-vers POE::Filter
1.2357

I recently received a nice Honeywell weather station. It turns out they are actually manufactured by a company called Irox which also sells stations under it’s own name but they seem to be more popular in Europe. Being a geek, one of the first things I did was check out Linux or OS X support. Unfortunately only one piece of software supports this weather station under Linux, Weather Display. There Linux software is freeware but not open source and leaves quite a bit to be desired but at least it would talk to the weather station and collect data from it.

With a bit of Googling I found Saratoga Weather which seems to be based on a template from Carter Lakes. Unfortunately the PHP code is a bit of a mess with 43 separate php files all in a top level directory and including each other. With a bit of work I was able to bend it to my will but every little change was a pain to accomplish.

I started slowly re-implementing things in Perl. I found an online WD data-file parser which greatly helped in figuring out what the fields in Weather Displays native log files meant. Fast-forward a couple of weeks and I think things are pretty much done feature wise. I lack NWS warning/watch/advisory notification, the thermometer image with today’s information is still PHP generated, and I don’t yet have a wind graph. These last few details shouldn’t take too much work when I get around to it. I also have a few features the original lacks, graphs, a daily tweet with today’s high/low, and sane code :p.

The information from my weather station is available online at http://weather.thegrebs.com/ and the source is available via git clone from http://git.thegrebs.com/git/wxperl. You may also browse the repo via Git Web at http://git.thegrebs.com/?p=wxperl.

Ruby’s not Ready at glyphobet

Typical voltage divider, matched would have made better sense but the thermistor was a random one salvaged from consumer electronics so I didn’t know the value in advance.

Would work just fine like this with TP1 connected to an Arduino analog input and Vcc and GND connected. Energy savings for the win though, connected the top of the divider (Vcc) to a digital pin on the Arduino. Set the pin HIGH when you want to take a reading, LOW the rest of the time. Now the divider is not consuming power when a reading isn’t being taken.

Arduino Code

int pinDivEn   = 4;
int pinDivRead = 1;
int pinLED     = 13;

void setup() {
    Serial.begin(9600);
    pinMode(pinLED, OUTPUT);
    pinMode(pinDivEn, OUTPUT);
    Serial.println("READY");
}

void loop() {
    if (Serial.available() > 0) {
        digitalWrite(pinDivEn, HIGH);
        digitalWrite(pinLED, HIGH);
        delay(100);
        while (Serial.available() > 0)
            int serByte = Serial.read();
        Serial.println(analogRead(pinDivRead));
        digitalWrite(pinDivEn, LOW);
        digitalWrite(pinLED, LOW);
    }
}

pinDivEn is the divider enable pin (Vcc), pinDivRead is the analog input connected to TP1 in the divider, pinLED is is a digital pin with an LED that is lit while a reading is taken.

Once the Arduino boots it sends READY on the serial port at 9600 bps. It then waits for any data to be available on the serial port, when bytes are available, the voltage divider is enabled, the LED is lit, the bytes on the serial port are consumed, the value of TP1 is read and then written to the serial port, the divider enable pin is brought back low and the led is extinguished.

Perl Code

#!/usr/bin/perl

use strict;
use warnings;

use IO::Handle;
use Device::SerialPort;

my $dev = tie (*FH, 'Device::SerialPort', "/dev/tty.usbserial-A4001JwW")
    || die "Can't tie: $!";

$dev->baudrate(9600);
$dev->databits(8);
$dev->parity("none");
$dev->stopbits(1);

open (my $log, '>>', 'ohms.log') || die "can't open: $!";
$log->autoflush(1);

# wait for arduino to boot
while (1) {
    my $val = <FH>;
    last if $val;
}

print FH "1\n";
while (1) {
    my $val = <FH>;
    next unless $val;
    chomp $val;

    my $vR2 = $val / 1023 * 5;
    my $vR1 = 5 - $vR2;
    my $i   = $vR1 / 1_000 * 1_000;
    my $R2  = $vR2 / $i;

    print $log time . ' ' . $R2 . "\n";
    # printf("V_R2=%.2fV, i=%.2fmA  R2=%.2fK&#8486;\n", $vR2, $i, $R2);

    sleep 10;
    print FH "1\n";
}

Opens the serial port, waits for something (the Arduino sending ‘READY’ but it pays no attention to what) on the serial port then every 10 seconds sends a 1\n to the Arduino prompting it to send a value. The result of analogRead is an integer from 0 - 1023 so this is converted to a voltage. The current through the divider is found allowing the resistance of the thermistor to be solved for. The resistance and time are written to a space separated log file. If the thermistor wasn’t unknown it would make more sense to solve for the actual temp using the Steinhart–Hart equation or similar and logging that rather than the resistance.

Sample log file entries
1224349429 10.1195652173913
1224349439 10.3666666666667
1224349449 10.3666666666667
1224349459 10.3666666666667
1224349469 10.4943820224719
1224349479 10.3666666666667
1224349489 10.2417582417582

A few lines in a text file gets us a graph from the log file by way of GnuPlot:

set term png transparent nocrop enhanced font "./arial.ttf" 9 size 800, 600
set xdata time
set timefmt "%s"
set format x "%m/%d %H:%M"
set xtics  rotate by -45
set title "Thermistor Value"
set xlabel "Date/Time"
set ylabel "Resistance (kOhms)"
set grid
set output "ohms.png"
plot \
    "ohms.log" using 1:2 title "10 sec interval readings" linecolor 2, \
    "ohms.log" using 1:2 title "Bezier fit curve" smooth bezier linecolor 4 lw 2, \
    10 title "77 F" lw 2 linecolor 1