Creating a weather station with Linux
Long ago I decided that I wanted to keep track of local weather. This is somewhat related to my desire to keep an eye on my raised bed gardens during the summer and partially due to my desire to have fun electronics projects to keep me doing “fun things”. I had already started with 1-wire and had a few devices that I either purchased or made myself.
As a first pass, I decided to see if I could get all my sensors working using Linux before attempting and Arduino conversion. That said, It would have been easier if I had decided to use Windows and follow Tim Bitson’s examples from his “Weather Toys” book. The book provides guidance for MacOS and Windows only. That’s really not a show stopper though as I was able to get everything working.
Step 1: Install Linux
Install Ubuntu Linux workstation version 9.10 LTS (I tried newer versions but they have some annoying issues)
Step 2: Installing JavaVM and RXTX
Note: A version of Java is installed by default, It’s just not the one I want.
I installed the full suite of latest SUN JAVA (not default OPENJDK and note that the SUN install requires enabling partner repositories – Google for instructions about enabling and then the JAVA install is simple)
Install RXTX with the command
sudo apt-get install librxtx-java
(It does all the tricky bits for you)
Step 3: OneWire support for JAVA
Download OneWireAPI “http://files.dalsemi.com/auto_id/public/owapi_1_10.zip”
Extract contents to a convenient location and get setup to copy files.
Copy the file OneWireAPI.jar to /usr/share/java/OneWireAPI.jar
The Java Libraries get installed to /usr/share/java. This is default behavior for librxtx-java install, so I used the same solution for OnewireAPI (manually copied)
Step 4: NETBEANS
In my case, this is version 6.8, installed from Synaptic Installer or you could use:
sudo apt-get install netbeans
Netbeans will create a project directory by default in your home folder. Your code goes here.
Libraries:
When defining the library settings for NETBEANS, it’s as simple as the two entries in the “libraries” section, as shown in the book.
a) /usr/share/java/OneWireAPI.jar
b) /usr/share/java/RXTXcomm.jar
Step 5: Grab WEATHERTOYS code.
General Notes
I use the AAG TAI603B interface (USB-SERIAL & 1 Wire Power Injector with home made Hobby Boards adapter) and this is automatically recognized as a device by this version of Linux. In my case, it is a serial device, coded as:
public static final String ONE_WIRE_SERIAL_PORT = "/dev/ttyUSB0";
and seen by the API as:
public static final String ADAPTER_TYPE = "DS9097U";
You can find the ports available with the following command:
sudo dmesg | grep tty
You will likely see something like:
"/dev/ttys0" or "/dev/ttyUSB0"
Barometric Pressure
While looking at low cost pressure sensors in the Mouser Electronics catalog, I located the FREESCALE MPXAZ6115A as a possible sensor for my project. The sensor has the following statistics;
Device: MPX6115, MAX PSI 16.7, MAX kPa 115.
Since barometric pressure here hovers at around 100kPa or so, this sensor would do just fine. The analog output of the sensor is relative to the min/max pressure range of the sensor.
According to my initial tests, the sensor would output about 4.06 volts at 100kPa.
The built-in analog input on the Arduino would also keep the circuit simple and after a few tests I was able to determine the offset value I needed to get correct readings for the localized barometric pressure.
In my case… testing showed that the magic number is 0.13.
// Nominal Transfer Value:
// Vout = VS x (0.009 x P – 0.095)
// ± (Pressure Error x Temp. Factor x 0.009 x VS)
// VS = 5.1 ± 0.25 Vdc
float Vin;
float P;
void setup()
{
Serial.begin(9600);
}
void loop()
{
Vin = (5.0/1024.0) * analogRead(0);
Vin = Vin + 0.13; // Offset Adjustment
Serial.print(Vin);
Serial.println(" Volts");
P=((Vin/5.0)+0.095)/0.009;
Serial.print(P);
Serial.println(" kPa");
Vin = (P * 0.2952999);
Serial.print(Vin);
Serial.println(" Inches of Mercury");
delay(2000);
}
I’m using a LADYADA Boarduino on a solder-less breadboard for testing. The sensor hookup is dead simple with only one exception that makes it tricky. The part I selected is designed to be surface mounted.
I decided to create a carrier board using the board layout software I prefer called SprintLayout from ABACOM in Germany. Other than 5V power and ground connections, the Vout from the carrier board goes directly to the Arduino Analog(0) pin.
To create the PCB board, I use the GOOTIE toner transfer method to apply the layout on the PCB for etching. (google search “gootie PCB” for more info)
Having developed a dislike for the chemical etchant that Radio Shack sells; Ferric Chloride, I have also adopted the etchant that
Gootie describes.
It is based on the swimming pool chemical Muratic Acid and Hydrogen Peroxide in a 1 to 2 ratio. It’s fast, non-opaque and does not require heating or excessive agitation.
Note: I also recently picked up a used GBC Creative Laminator at the local Goodwill for $14.00. It does an excellent job of applying the toner to the copper on the PCB to be etched. Using an hand iron was OK, but the results were not always predictable.
Here is the Layout:
Legacy Recovery: Arduino and Parallax SHT-11 BoB
July 3, 2008
As a part of my ongoing project and seemingly never ending interest in what’s going on outside my window, I purchased a a PARALLAX humidity and temperature sensor. Basically, the Parallax part is a surface mount Sensirion Temperature/Humidity Sensor nicely mounted on a PC board that has 8-PIN DIL pin out for insertion into a solder-less breadboard.
It’s available from MOUSER and from PARALLAX directly.
To get it working, the circuit itself is dead easy. The Parallax part has additional SMD pullups and capacitors right in the 8-pin DIL package so we are only dealing with a few wires. I don’t even need to really show a schematic… the details are in the code.
The code is not really my own creation at all. It is a collection of good ideas from others who have already dealt with this device.
//==========================================================================//
// //
// SHT-11 Humidity & Temperature Version 1.00 December 2008 //
// //
// NOTICE: This is for ARDUINO IDE VERSION 18! //
// Some methods used are no longer needed. //
// //
// Written for the Arduino ATmega168 Diecimila and installed and tested //
// on December 12,2008 //
// //
// Multiple Internet references were used, combined and modified //
// for this example, such as Arduino forums and nuelectronics.com //
// //
//==========================================================================//
// Devices Used: //
// Boarduino: USB Powered - Diecimila //
// http://www.ladyada.net/make/boarduino/index.html //
// The Boarduino is a Solderless Breadboard compatible Arduino //
// //
// Parallax Sensirion SHT-11 module //
// http://www.parallax.com (Look for "SensirionDocs.pdf" ) //
// //
// The parallax module is a breadboard compatible carrier //
// with the SMD sensor installed by parallax //
// NOTE: Different Pinout than SMD sensor from Sensirion //
//==========================================================================//
// Notes: //
// //
// The Parallax module contains built-in Pullup and Data Pin resistors //
// Sensor Carrier Boarduino //
// Data Pin 1 -- Arduino pin 10 //
// Clock Pin 3 -- Arduino pin 11 //
// Vss Pin 4 -- Arduino GND //
// Vdd Pin 8 -- Arduino 5V //
//==========================================================================//
//==========================================================================//
// Preamble //
//==========================================================================//
#define LED 13
#define T_CMD 0x03 // See Sensirion Data sheet
#define H_CMD 0x05
#define R_STAT 0x07
#define W_STAT 0x06
#define RST_CMD 0x1E
//==========================================================================//
// SHT11 Sensor Coefficients from Sesirion Data Sheet
const float C1=-4.0; // for 12 Bit
const float C2= 0.0405; // for 12 Bit
const float C3=-0.0000028; // for 12 Bit
//const float D1=-40.0; // for 14 Bit @ 5V
//const float D2=0.01; // for 14 Bit DEGC
const float T1=0.01; // for 14 Bit @ 5V
const float T2=0.00008; // for 14 Bit @ 5V
//==========================================================================//
// Sensor Variables
int shtClk = 11; // Clock Pin
int shtData = 10; // Data Pin
int ioByte; // data transfer global - DATA
int ackBit; // data transfer glocal - ACKNOWLEDGE
float retVal; // Raw return value from SHT-11
float temp_degC; // working temperature
float temp_degF; // working tempeature
float r_temp; // raw working temp
float r_humid; // Raw working humidity
float dew_point;
float dew_pointF;
//==========================================================================//
// coding variables
int dly;
int timewait;
byte bitmask;
//==========================================================================//
// //
// Code Body //
// //
//==========================================================================//
void setup()
{
pinMode(shtClk, OUTPUT); // Initialize the pins
digitalWrite(shtClk, HIGH); // Clock
pinMode(shtData, OUTPUT); // Data
pinMode(LED, OUTPUT); // LED
Serial.begin(9600); // open serial Port for 9600 Baud
Serial.println("Resetting Sensor..");
SHT_Connection_Reset();
// Fast Flash LED to say we are ready
digitalWrite(LED, HIGH);
delay(500);
digitalWrite(LED, LOW);
delay(500);
digitalWrite(LED, HIGH);
delay(500);
digitalWrite(LED, LOW);
//-----------------------------
Serial.println("Starting Temperature & Humidity reading every 5 seconds.");
}
//==========================================================================//
void loop()
//==========================================================================//
{
// SHT-11 Get Temperature
Serial.println("------------------------------------------------------------------------------");
SHT_Measure(T_CMD); // retVal = Temperature reading
r_temp = retVal;
temp_degC = SHT_calc_tempC( retVal); // Convert to Celcius
Serial.print("Temperature: ");
serialPrintFloat(temp_degC);
Serial.print("C");
Serial.print('\t');
temp_degF = SHT_calc_tempF( retVal); // Convert to Fahrenheit
Serial.print("| Temperature: ");;
serialPrintFloat(temp_degF);
Serial.print("F");
Serial.print('\t');
Serial.println();
// SHT-11 Get Humidity
SHT_Measure(H_CMD); // retVal = humidity reading
r_humid = retVal; // Store raw humidity value
Serial.print("Humidity: ");
// Linear conversion
float rh_lin = C3 * retVal * retVal + C2 * retVal + C1;
// Temperature compensated RH
float rh_true = (temp_degC * (T1 + T2 * retVal) + rh_lin);
if(rh_true>100)rh_true=100; // deal with rh being outside
if(rh_true<0.1)rh_true=0.1; // a physical possible range
serialPrintFloat(rh_true);
Serial.print("%");
Serial.print('\t');
// calculate Dew Point
dew_point=calc_dewpoint(rh_true,temp_degC); //calculate dew point
dew_pointF = 9 * dew_point/5 + 32;
Serial.print("| Dew point: ");
serialPrintFloat(dew_point);
Serial.print("C");
Serial.print(" ");
serialPrintFloat(dew_pointF);
Serial.print("F");
Serial.println();
// Slow Flash activity LED and create pause between scans
// ...in this case, 5 secs)
timewait = 0;
while (timewait < 5)
{
digitalWrite(LED, HIGH);
delay(500);
digitalWrite(LED, LOW);
delay(500);
timewait++;
}
}
//--[ Subroutines ]---------------------------------------------------
void SHT_Write_Byte(void)
{
pinMode(shtData, OUTPUT);
shiftOut(shtData, shtClk, MSBFIRST, ioByte);
pinMode(shtData, INPUT);
digitalWrite(shtData, LOW);
digitalWrite(shtClk, LOW);
digitalWrite(shtClk, HIGH);
ackBit = digitalRead(shtData);
digitalWrite(shtClk, LOW);
}
//--------------------------------------------------------------------
int shiftIn()
{
int cwt;
cwt=0;
bitmask=128;
while (bitmask >= 1)
{
digitalWrite(shtClk, HIGH);
cwt = cwt + bitmask * digitalRead(shtData);
digitalWrite(shtClk, LOW);
bitmask=bitmask/2;
}
return(cwt);
}
//--------------------------------------------------------------------
void SHT_Read_Byte(void)
{
ioByte = shiftIn();
digitalWrite(shtData, ackBit);
pinMode(shtData, OUTPUT);
digitalWrite(shtClk, HIGH);
digitalWrite(shtClk, LOW);
pinMode(shtData, INPUT);
digitalWrite(shtData, LOW);
}
//--------------------------------------------------------------------
void SHT_Start(void)
{
// generates a sensirion specific transmission start
// This where Sensirion is not following the I2C standard
// _____ ________
// DATA: |_______|
// ___ ___
// SCK : ___| |___| |______
digitalWrite(shtData, HIGH); // Data pin high
pinMode(shtData, OUTPUT);
digitalWrite(shtClk, HIGH); // clock high
digitalWrite(shtData, LOW); // data low
digitalWrite(shtClk, LOW); // clock low
digitalWrite(shtClk, HIGH); // clock high
digitalWrite(shtData, HIGH); // data high
digitalWrite(shtClk, LOW); // clock low
}
//--------------------------------------------------------------------
void SHT_Connection_Reset(void)
{
// Connection reset: DATA-line=1 and at least 9 SCK cycles followed by start
// 16 is greater than 9 so do it twice
// _____________________________________________________ ________
// DATA: |_______|
// _ _ _ _ _ _ _ _ _ ___ ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |__| |______
shiftOut(shtData, shtClk, LSBFIRST, 0xff);
shiftOut(shtData, shtClk, LSBFIRST, 0xff);
SHT_Start();
}
//--------------------------------------------------------------------
void SHT_Soft_Reset(void)
{
SHT_Connection_Reset();
ioByte = RST_CMD;
ackBit = 1;
SHT_Write_Byte();
delay(15);
}
//--------------------------------------------------------------------
void SHT_Wait(void)
{
// Waits for SHT to complete conversion
delay(5);
dly = 0;
while (dly < 600)
{
if (digitalRead(shtData) == 0) dly=2600;
delay(1);
dly=dly+1;
}
}
//--------------------------------------------------------------------
void SHT_Measure(int SHT_CMD)
{
//--------------------------------------------------------------------
SHT_Soft_Reset();
SHT_Start();
ioByte = SHT_CMD;
SHT_Write_Byte(); // Issue Command
SHT_Wait(); // wait for data ready
ackBit = 0; // read first byte
SHT_Read_Byte();
int msby; // process it as Most Significant Byte (MSB)
msby = ioByte;
ackBit = 1;
SHT_Read_Byte(); // read second byte
retVal = msby; // process result to combine MSB with LSB
retVal = retVal * 0x100;
retVal = retVal + ioByte;
if (retVal <= 0) retVal = 1;
}
//--------------------------------------------------------------------
int SHT_Get_Status(void)
{
//--------------------------------------------------------------------
SHT_Soft_Reset();
SHT_Start();
ioByte = R_STAT;
SHT_Write_Byte();
SHT_Wait();
ackBit = 1;
SHT_Read_Byte();
return(ioByte);
}
//--------------------------------------------------------------------
int SHT_calc_tempC( float w_temperature)
//--------------------------------------------------------------------
{
// calculate temp with float
float temp1;
// Per the data sheet, these are adjustments to results
temp1 = w_temperature * 0.01; // divide by 100
temp1 = temp1 - (int)40; // Subtract 40
return (temp1);
}
//--------------------------------------------------------------------
int SHT_calc_tempF( int w_temperature)
{
// calculate temp with float
int temp1;
temp1 = w_temperature * 0.018;
temp1 = temp1 - (int)40;
return (temp1);
}
//--------------------------------------------------------------------
float calc_dewpoint(float h,float t)
// calculates dew point
// input: humidity [%RH], temperature [°C]
// output: dew point [°C]
{
float logEx,dew_point;
logEx=0.66077+7.5*t/(237.3+t)+(log10(h)-2);
dew_point = (logEx - 0.66077)*237.3/(0.66077+7.5-logEx);
return dew_point;
}
//--------------------------------------------------------------------
void serialPrintFloat( float f)
{
// print results properly with float decimal value
int i;
Serial.print((int)f);
Serial.print(".");
i = (f - (int)f) * 100;
Serial.print( abs(i) );
}
TouchPad Hacking
HP did a nice thing for it’s employees recently. After the unannounced fire sale of HP Touchpad’s at retailers, they offered up a similar sale for employee purchase. Needless to say, more than a few employees took advantage of the offer.
Now to be fair, I never really intended to use it “as is”. I was “this close” [hold thumb and index finger really close together] to buying a NOOK Color for hacking purposes and when this opportunity arose… I knew it would be just a matter of time before someone developed a Google Android OS solution to offset the rather limp offerings in the WebOS application market.
It didn’t take long. Now after the second patch of the Alpha release of CyanogenMod 7 for the HP Touchpad, I can say that this is an excellent Android platform. I could actually see HP tweaking it a bit and allowing it to become an awesome Android tablet… but that is some wishful thinking on my part.
In: General Rants, Uncategorized
I’m Back.
Back from the virtual grave. Lets so how things go from here…
What’s new?
Fry’s Retail Stores now sell arduino variants right off the shelves… including the mega2560. This is good news!
By the way:
Hosting companies that don’t warn they are closing up shop or even say goodbye are rather cowardly. No happy feelings towards Johnnie Nelke of the now defunct ”HostingRevolution” right now. If anyone ever sits down next to this guy at a bar, smack him for me.
In: General Rants, Uncategorized