Feb

4

One Wireduino made easy

16 years ago, at the start of February | 12 Comments

For a very long time now I’ve been playing with the Arduino boards but it wasn’t until I recently discovered some DS1820 1-wire chips in my parts box that I started even thinking about 1-wire stuff. Connecting 1-wire devices to the Arduino is, well, amazingly simple. Using the sample circuit from the datasheet we can see the connections are few and far between.

Please note that this is the corrected circuit, previously the VDD was not tied to ground. While the circuit would work it would only give reliable results on very short runs. This circuit allows longer runs to the sensor.

Coding this up is also made extremely easy with the OneWire library. I’ve put together a little application below that will read all of the 1-wire devices on a bus. If you press L in the Arduino IDE serial monitor it will list all the 1-Wire device id’s and if you press T you’ll get the id and temperature reading.

/*
Simple 1-wire device reading
 
Pass T over serial to get temperatures
Pass L to list 1-wire devices
 
*/
#include <OneWire.h>
#include <stdio.h>
 
#define CONVERT     0x44
#define READSCRATCH 0xBE
#define SKIP_ROM    0xCC
#define MATCH_ROM   0x55
 
OneWire  ds(10);  // The DS18S20 is connected on pin 10
int ledPin = 13;  // flash an led on 13 - we all like flashing lights
 
void setup(void) {
  // initialize inputs/outputs
  // start serial port
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);  //we'll use the led to output a heartbeat
}
 
void loop(void) {
  int incomingByte = 0;
  if (Serial.available() &gt; 0) {
		// read the incoming byte:
		incomingByte = Serial.read();
 
		// say what you got:
		//Serial.print("I received: ");
		//Serial.println(incomingByte, DEC);
                if (incomingByte == 84) {
                  getStuff();
                  Serial.print("\r\n^");
                } else if (incomingByte == 76) {
                   listDevices();
                }
	}
 
}
 
void listDevices(void) {
 
  byte addr[8];
 
  ds.reset_search();
 
  while(ds.search(addr)) {
 
     digitalWrite(ledPin, HIGH);   // sets the LED on
 
     if ( OneWire::crc8( addr, 7) == addr[7])   {
         if ( addr[0] == 0x10) {
            // Make sure it is a DS18S20 device
            char buffer[512];
            sprintf(buffer,"Id:%02x%02x%02x%02x%02x%02x%02x%02x\r\n",
                       addr[0], addr[1], addr[2], addr[3], addr[4],
                       addr[5], addr[6], addr[7]);
              Serial.print(buffer);
          }
      }
  }
 
    Serial.print('^');
}
 
void getStuff(void) {
  byte i;
  byte present = 0;
  byte data[12];
  byte addr[8];
  char buff[15];
  float real_temp;
 
  float temp_count;
  float read_temp; 
 
  ds.reset_search();
 
  while(ds.search(addr))  {
 
     digitalWrite(ledPin, HIGH);   // sets the LED on
 
    if ( OneWire::crc8( addr, 7) != addr[7])  { // Check CRC is valid
        Serial.print("CRC is not valid");
    }
 
    if ( addr[0] != 0x10) {   // Make sure it is a DS18x20 device
      Serial.print("Device is not a DS18x20 family device.");
    }
 
    ds.reset();    // Reset device
    ds.select(addr);     // Select device
    ds.write(CONVERT,1);   // Issue Convert command 
 
    delay(1000);     // maybe 750ms is enough, maybe not
    digitalWrite(ledPin, LOW);    // sets the LED off
 
    present = ds.reset();  // Reset device
    ds.select(addr);  // Select device
    ds.write(READSCRATCH);  // Read Scratchpad
 
    for ( i = 0; i &lt; 9; i++) {  // we need 9 bytes
          data[i] = ds.read();
    }
 
    if(OneWire::crc8( data, 8) == data[8]) {  // Check CRC is valid
 
      // CRC is ok
      // Divide the temperature by 2 - note the » and
      // « need to be replaced with double < and >
      // wordpress kills the server when you try to 
      // save otherwise.
      read_temp=((data[1]«8) | data[0]) » 1 ;
     // Convert to real temperature
      temp_count=float(data[7] - data[6])/(float)data[7];
      real_temp = ((float)read_temp-0.25)+temp_count;
 
       // Convert float to ascii
      tempToAscii(real_temp,buff);
      char buffer[512];
      sprintf(buffer,"%02x%02x%02x%02x%02x%02x%02x%02x %s\r\n",
                  addr[0], addr[1], addr[2], addr[3], addr[4],
                  addr[5], addr[6], addr[7], buff);
 
      Serial.print(buffer);
 
    } else    {
       Serial.println("CRC Failed");
    }
  }    
 
void tempToAscii(double temp, char *buff) {
  int frac;
  //get three numbers to the right of the decimal point
  frac=(unsigned int)(temp*1000)%1000;
  itoa((int)temp,buff,10);
 
  strcat(buff,".");
  //put the frac after the decimal
  itoa(frac,&amp;buff[strlen(buff)],10);
}

There’s also a copy of the .pde file that you can download if you feel more inclined. It’s not an exact copy, I removed the commented out xml for the above version. It’s worth pointing out that this circuit is using what is called parasitic power, which means your cable run should be shortish. If you want to use an external power supply then pin 3 (VDD) on the DS18S20 should go to your external supply. This would allow for much longer runs of cable. Below is an example graph generated by cacti with 2 DS1820’s connected the the arduino. As you can see the temperatures aren’t exactly the same but this is to be expected since the accuracy of the DS1820 is +/- 0.5 ° C

The breaks in the graph were caused my me removing the USB plug from the PC it was connected to so that I could make some minor alterations to the circuit.

Josh asked how I was getting the input for Cacti, here’s the perl script I use

#!/usr/bin/perl
 
$output = `echo -en "T" >>/dev/ttyUSB0 && cat /dev/ttyUSB0`;
 
@lines = split(/\r\n/,$output);
$t=1;
 
foreach $line (@lines) {
 
       @spl = split(/\s+/,$line);
 
	$lc = @spl;
 
	if ($lc gt 1) {	
                $node=$spl[0];
		$val=$spl[1];
 
		print "Temperature_$node:$val ";
	}
$t++;
}

This outputs Temperature_x:n where x is the 1-Wire id and n is the temperature. It could probably do with tidying up and if you wanted to you could pass the 1-Wire id to the script to and only output the temperature for that particular 1-Wire device. A copy of the exported Cacti template can be downloaded, I’m hoping that you just need to import that into your Cacti after placing the script in the scripts directory. Just remember, under linux, if you unplug and replug in your Arduino you may need to set the tty port speed to 9600 (or whatever you put in your Serial.begin(); ). You can use the following command for that;

1
2
3

 
 
stty -F /dev/ttyUSB0 cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts

Make sure that ttyUSB0 is what your Arduino is connected to first. If not you will need to change it in the perl script and on the line above.

Tagged with: 1-Wire • arduino • hardware • opensource • software
February 4, 2009 21:46

Jan

12

WordPress tweetbacking

16 years ago, mid-January | 4 Comments

Tweetbacking, it sounds like some sort of deviant sport or something but isn’t. The idea behind Tweetbacks, similar to pingbacks, is that you can see who is commenting (tweeting) about your blog on Twitter. There are a number of plugins available for use in the end I went for Joost de Valk‘s version. While it worked nicely I decided that I really wanted to approve the tweets before they appeared in my blog so I modified the code a little. The diff is available for download. It allows you to enable and disable the automatic approval of Tweets form the plugin’s admin page. Hopefully Joost will add this option in the official version sometime.

Tweetbacks are saved in the comments table and can be displayed however you like for example, in my comment loop I have:

 
<?php 
if (strtolower($comment->comment_type) == 'tweetback') {
   $avatarurl = str_replace(
       "twitter:",
       "http://s3.amazonaws.com/twitter_production/profile_images/",
       $comment->comment_author_email
       );
       echo "<img align=middle"
              ." src='$avatarurl' border=none"
              ." width=40 height=40 alt=''>";
}
?>

A word or two of caution about the plugin. Personally I’ve removed the bit.ly url shortening link parsing because it just didn’t work properly – I ended up with bogus tweetbacks until I did. The other issue is with the date saving from the tweetback, it doesn’t work properly either giving dates in the 1970’s!!!

Tagged with: opensource • software
January 12, 2009 22:09

Nov

28

iPhone proximity sensing IS in the API

17 years ago, at the end of November | Leave a Comment

There seems to have been a lot of misinformation flying about of late. With Google releasing a new version of their app incorporating proximity sensing, some blogs have claimed this is breaking AppStore rules by using undocumented hidden (non public) API calls. I’m here to tell you that’s just rubbish. All that has happened is the people reporting it haven’t even bothered to check. Want to prove this to yourself?

1. Start Xcode and pick one of the templates.
2. Load up the AppDelegate code and skip to ‘applicationDidFinishLaunching’.
3. Type ‘application.’ (note the full stop after the word application)
4. Hit escape and you’ll get a list, scroll down to items starting with P
5. Oh look there it is…

For those without Xcode here’s a picture.

Oh, that must be the non-public public api...

For those that want to see the what the documentation says

proximitySensingEnabled


A Boolean value that determines whether proximity sensing is enabled.
@property(nonatomic, getter=isProximitySensingEnabled) BOOL proximitySensingEnabled
Discussion

YES if proximity sensing is enabled; otherwise NO. Enabling proximity sensing tells iPhone OS that it may need to blank the screen if the user’s face is near it. Proximity sensing is disabled by default.
Availability
Available in iPhone OS 2.0 and later.
Declared In

UIApplication.h

Unfortuneately once some people grab hold of false information no facts will get in their way. Anyone that knows me will tell you that I’m really not fond of either Google or Apple, but let’s just get stuff right shall we.

Update: I’ve had some discussion on irc and it was felt that I should point out that proximityStateChanged is used and following some additonal chatter on IRC with UncleBob who pointed out that “It’s not private in the OBjC sense just the Apple documented SDK sense. ” he then went on to say “the whole thing is definately a peanut-gallery cockfest” which sums it all up really.

_{»crosslinked«}

Tagged with: api • Apple • google • iphone
November 28, 2008 11:43

Nov

11

Concept iPhone Application

17 years ago, mid-November | 3 Comments

I’ve been messing about trying to learn how to write iPhone apps. There’s a lot to take in but at the moment I’ve managed a concept application. A little shop (of horrors ;). At the moment it simply reads data from an sqlite database and then displays information on the product. The buy now button currently just jumps to the product url at Linitx.com.

Update: Added a screenshot when rotated. The iPhone SDK handles the rotation automatically, all you need to do is specify which parts of which objects move or resize. All that can be done from Interface Builder. Easy as pie. Also note the changed title bar colour, in keeping with LinITX, and the title text. The shop title (LinITX) and shop base product URL are read from a plist file. I suppose they could be read from the sqlite db but I am experimenting so learning how to read a plist file is useful too.

Update 2: Spent ages last night trying to work out why some of the text descriptions for products came out of the database as null. Discovered that when importing the data file it wasn’t using UTF8 encoding, which is apparently all sqlite deals with. Loading up the source data file into TextEdit under OSX and saving it as UTF8 then reimporting solved the problem. I also modified how things are displayed. The image and text are inserted into a UIWebView so are now scaleable by the user. The images are also base64 encoded and in the database. This increases the database size but means the application can still be used offline. Before none of the pictures would display if there was no network connectivity.

Update 3: Added the ability to search the list. The search bar appears when the search button is pressed and hides again when the search is complete.

Tagged with: development • iphone • software
November 11, 2008 20:35

Oct

19

Fullscreen iPhone WebApps

17 years ago, mid-October | 1 Comment

Web applications on the iPhone have always been second class citizens without access to the really interesting features. To add insult to injury web applications lost a large chunk of screen real estate to the top and bottom Safari toolbars.

Well, now they don’t need to. For users with firmware 2.1, if you add the following lines to the <head> section of your web application page then, when someone adds your web application to their home screen and then uses it all they will see is the standard bar showing carrier name, signal and battery level. As ever the pictures should make it much clearer. Notice that there is no address bar or lower toolbar at all, even when scrolling.
Read more…

Tagged with: Apple • iphone
October 19, 2008 16:44

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