Wow that a long time since my last post

Wow , it`s a long time since I`ve updated my blog , and lot have happened in my embedded computer world .

It the last year I have added the following platforms to my collection .

MBED ( Arc Pro ) , Cubietruck and my latest the Udoo .

tmp102 for the Raspberry Pi

I`ve been using the tmp102 for a couple , but never really got to grips with how to deal with minus temperatures.
If you want a good night sleep try reading and fully understanding it`s pdf document .
I can now understand just about any spi or i2c device document, But this a is most harder to decipher.

http://www.ti.com/lit/ds/symlink/tmp102.pdf

How to read from the chip :

It`s I2C address depend on where you connect the ADD0 too.

Ground = 0x48 , V+ = 0x49 , SDA = 0x4A , SCL = 0x4B


Read two Bytes  ( High byte is first followed by the Low byte )

High byte ( Full degrees )
Low byte ( fraction degrees )


To get the temperature
Multiply the Hi_byte by 16 ( <<  4 )  +  Divide Low_byte by 16 ( >> 4 )
Now multiply the result by 0.0625 and you have the temperature.

Temperature = (( Hi_byte << 4) | ( Low_byte >> 4)) * 0.0625  

This works if the temperature is above zero.

Minis temperature problem
The most significant bit of High byte says if the temperature is a negative or positive value.
The documents explanation on how to convert the negative value is:-

For negative temperatures (for example, –25°C):
Generate the twos complement of a negative number by complementing the absolute value binary number
and adding 1. Denote a negative number with MSB = 1.
Example: (|–25°C|)/(0.0625°C/count) = 400 = 190h = 0001 1001 0000
Twos complement format: 1110 0110 1111 + 1 = 1110 0111 0000

My way I converting this into a usable form , is to test if the most significant bit is set  :-

if Hi_byte & 0x80 == 0x80:

If this is True we need to add 1 to the Hi_byte and remove any overflow and keep the value byte size  :-

Hi_byte = (Hi_byte + 1 & 0xff) 

This don`t work in fact , after waiting for it to freeze to test out my code.

I`ve found the way to do it , is 

0 - ( 256 - Temperature )  

To download the complete working code for python 3 using Quick2wire my link is below.
This can be converted to any i2c library , all you need is the High and Low byte.

 https://github.com/peter247/Pi_Weather_monitor/blob/master/examples/tmp102.py

Setting up a git Repository

After finding that Blogger is not the ideal method to post any code I thought it was time to learn how to make a git repository for any my code.

I have used git many times before but only used git to get code from the repository using git clone git:repository.
They say learning from your mistakes help you to learn, then I`ve done a lot of learning with this excise .

If there is a way to get it wrong I`ve made it.  

I had all ready install all the relevant modules for downloading code:
 eg git and git-core.

I followed the instruction from :  

https://help.github.com/articles/set-up-git
https://help.github.com/articles/generating-ssh-keys

Made my key pair because my raspberry pi didn`t have one by default ,   and posted it to the git repository ssh key profile screen.

Tried to load in  with "ssh -T git@github.com" , wow all worked !!!.
I now made my first repository and clicked on the option to add a readme file to start the repository off. 

This is where my mistakes started to come think and fast !!!!


I log in my Pi and did my normal way to download a git:repository using the read only method .

eg with "git clone git://github.com/my_account/project_name.git" big mistake I was later to find.

I started to read this :-
http://git-scm.com/book/en/Git-Basics-Recording-Changes-to-the-Repository

# Made a new file .
git add the_new_file
git commit -m "start off"
git push

from the push, got I you can`t push you "git://github.com/my_account/project_name.git" try using "git@github.com:my_account/project_name.git"

So I guess that was learn one.

I started to make a real project , and made a new project like before , but this time using the ssh address method.
I tried repeating the above excise making a new file , adding the file , committing the file , then pushing the file , wow no problems this time.
Copied my project to the project folder and did a "git add *" .
Them thought that`s a bad idea all my password and key files are still in my code , so for I haven`t committed the files yet, so I can still just remove them before committing the files. It didn`t work that way and after I pushed my files to the repository I could see my password and key files and commit showing the changes to these files.

So I guess that was learn two , Remove any bit you don`t want to be shown before you add them
  
It was delete and start again with 3rd time lucky.

My projects

This is a picture of my project bench.

Which is a change to now have a computer with i2c , spi and gpio support , and have full Linux instead of having to program in c or c++ like my other embedded platforms. ( Arduino , Fltyport )

I using a Raspberry Pi , which is hidden under my soldering iron unit in the photo.
on one breadboard directly connected to the Pi is a mcp3008 which is a spi , analogue to digital convertor,  a level shifter connected to a second breadboard feed with a external 5 volt power supply , so keep the 3.3 volt and the 5 volt chip on separate breadboards.
The second breadboard contains a mcp23017 i2c expander chip , half of the chip is been used for input via switches and the other half connected to a ULN2803a  , Darlington transistor array to power two rbg leds .

My two project which I`m playing with right now is :-

1/ MPC controller .
2/ Weather station / monitor .

The Music Player Daemon controller , which is finished unless I need to add a little after.  The switches control , pause / play ,  previous  , next , delete track from play list and drive , volume up and down , etc

The Weather station / monitor , which is a never ending story .
This project started on the Arduino moved to the Flyport and as now moved to the Raspberry Pi Model A I hope soon.

The project now monitors air temperature inside / outside and sends the data to cosm and thingspeak ,  the temperature changes the colour of the rbg led.
Too hot is red , too cold is blue and just nice is green .
The full project is controlling the solar powered garden lights , which is state of charge / discharge is monitored.

All in all , it learning about programming and the best way to learn is find a project you can add too , as more you learn the more complex to gets.

 
  


 

Wow , it is a long time since my last post

Wow , it`s a long time since I wrote anything in this blog. So I guess it is time to add my new projects and computers to the list. Most of my programming time is now on the Raspberry pi.

Flyport

Just got a new toy a Flyport :- http://www.openpicus.com/cms/

it time to find how it works and making my own project.

New Embembed micro

Hi , I`ve got a new embebbed micro to play with a BV513 from Byvac.

http://www.byvac.co.uk/bv/bv513.htm

So it`s back to learning a form of basic, which other than visual basic , most of my programing time as been spent learning to program in C or C++

And the good thing about this micro over the Arduino is the high amout of storage.
512k to 16k flash and 32k compared to 1k.