Raspberry Pi - RPOf project

The Raspberry Pi can be used to run some kind of embedded Linux.
Like any *nix system, removing suddenly power is not a  good thing, it is very easy to corrupt  some SD card sector if the power removal happens during a writing cycle.

Raspberry Pi - connecting a traditional LCD display (Update)

Raspberry Pi is a powerful enough platform and  it is possible to use many recent touchscreen with a nice graphic on it.
However often a traditional LCD is more useful, and surely is more cheap than a touchscreen solution.

Here one way to connect a traditional LCD and use it in projects, like the TeirmiLab one.
This article describes how to connect a traditional LCD but with RGB capabilities to the Raspberry Pi B.

We need :

• Raspberry Pi B or Raspberry Pi B+
• RGB 16x2 LED display
• MCP23017 I2C GPIO expander

It is possible to hook a display without the need of the GPIO expander, however a normal LCD uses at least 6 signals. 9 if the LCD display is an RGB one like the one used for this project.
Considering that the Raspberry Pi B doesn't have many GPIO available and that usually the speed required to handle the display is not critical, using a chip like the MCP23017 make sense.
In this way it will be enough to "hook" the  chip to the I2C bus, leaving all the Raspberry Pi GPIO free for other use.

Let see a schematic.

Software

There are many ways to control the hardware.
For now I found a ready-to-use Python library published by Adafruit that is working nicely.
Again, the important thing is that control an LCD is not a critical task, so a python script is Ok.
Maybe in future I'll explore the possibility to control it directly in C.

Python 

To use our display we need to install some code in our Raspberry.
Here a quick step-by-step guide (see Adafruit tutorials for a more detailed and easy instructions) :

1. sudo apt-get update
2. sudo apt-get install build-essential python-dev python-smbus python-pip
3. sudo apt-get install i2c-tools
4. sudo pip install RPi.GPIO
5. cd ~
6. git clone https://github.com/adafruit/Adafruit_Python_CharLCD.git
7. cd Adafruit_Python_CharLCD
8. sudo python setup.py install

Before to be able to use it, we need to be sure a configuration file is correctly set-up.

Execute : sudo nano /etc/modules

and if the file exists, add these two lines in the end.

i2c-bcm2708 

i2c-dev

Save the file then open another one in edit.
Execute : sudo nano /etc/modprobe.d/raspi-blacklist.conf

In this file comment out the two lines showed below, adding # at the beginning:

#blacklist spi-bcm2708

#blacklist i2c-bcm2708

Reboot Raspberry : sudo shutdown -r now

or : sudo reboot

At this point everything should be installed in order to use the display.

First is better to run an utility to see if the I2C GPIO expander is seen correctly.

sudo i2cdetect -y 1

The command should display a table and in the table should be present a 0x20 address.

pi@raspberrypi ~ $ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
pi@raspberrypi ~ $ 

If so, the chip is correctly seen by Raspberry.

To test if the display is working you can execute a test script :

1. cd Adafruit_Python_CharLCD/examples
2. sudo ./char_lcd_mcp.py

Some test messages should be displayed on the LCD display.

Troubleshooting

It is possible to have some problems installing the libraries.
Here a couple of tips and resolutions.

apt-get missing

If you start from a fresh installation of Raspbian, especially a lite version, before to start to follow the instructions above, be sure to execute :

• sudo apt-get update
• sudo apt-get upgrade
• sudo apt-get update

It is important because updating the first time, include more repo on apt-get.

python build fail

If during the python building of the library you have this errors :

python ./setup.py build

Downloading https://pypi.python.org/packages/source/s/setuptools/setuptools-3.5.1.zip

Extracting in /tmp/tmpw6UbTx

Traceback (most recent call last):

  File "./setup.py", line 4, in

    use_setuptools()

  File "/home/pi/Adafruit_Python_CharLCD/ez_setup.py", line 128, in use_setuptools

    return _do_download(version, download_base, to_dir, download_delay)

  File "/home/pi/Adafruit_Python_CharLCD/ez_setup.py", line 108, in _do_download

    _build_egg(egg, archive, to_dir)

  File "/home/pi/Adafruit_Python_CharLCD/ez_setup.py", line 57, in _build_egg

    with archive_context(archive_filename):

  File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__

    return self.gen.next()

  File "/home/pi/Adafruit_Python_CharLCD/ez_setup.py", line 88, in archive_context

    with get_zip_class()(filename) as archive:

  File "/usr/lib/python2.7/zipfile.py", line 770, in __init__

    self._RealGetContents()

  File "/usr/lib/python2.7/zipfile.py", line 813, in _RealGetContents

    raise BadZipfile, "File is not a zip file"

zipfile.BadZipfile: File is not a zip file

this happens because for some magic reason :) the python script screw up the download of a zipped file.

In my case the file was setuptools-3.5.1.zip.

Doing an ls -l showed up to be 122 byte big !! Definitively NOT a zip file.
The workaround was quite easy actually.

• remove the file : sudo rm setuptools-3.5.1.zip
• manually download the file :
  wget https://pypi.python.org/packages/source/s/setuptools/setuptools-3.5.1.zip 
• Re-execute the build : sudo python ./setup.py build

Examples

Be aware about the type of kit you are using.
On the examples area there are different examples depending the type of display in use.

To test the basic display, use : char_lcd_mcp.py
To test the kit with RGB display and pushbutton use : char_lcd_plate.py

Airflow sensor test

I used a little board with a MSP430-2013 and a LCD display  to develop the basic code to test and read the airflow sensor.

The circuit

Here a picture of the prototype

The software

The airflow sensor reading is based on counter and a timer.
The MSP430 pin connected to the airflow sensor is set in interrupt mode (rising) and after a check on the pin state to be sure is not a spike, a counter is incremented.
Every time a related timer expire, the value of the counter is copied into another variable (to be displayed) and the counter is reset.
I use another timer to display the read value on the display, after a integer-to-ascii conversion.
The code described is not reading the DS1820, only the airflow sensor.

TeirmiLab - prepare Raspbian

For the TeirmiLab project, one of the platform I choose to prototype it, is the Raspberry Pi B (or B+).

This is a quick step-by-step reminder about how to prepare Raspbian for the Raspberry Pi B and B+ for this project.

There are on-line hundreds of places where is described how to install a Raspbian over a Raspberry Pi.


If this quick step-by-step is not enough for you, try this.
If you think that this is too technical ... are you sure you want to play with microcontrollers ? :)

Lets start.
I used a 8 Gbyte micro SD card with a low profile adapter. In this way is easy to eventually swap to the Raspeberry Pi B+.

It is necessary, at least for the installation, to have :

• a 5 Volt 1A USB power supply
• a USB cable (microUSB) for the power supply
• an internet connection, better if wired
• a computer (needed to download the image and prepare the SD card)

Optionally if you want to enable the graphic interface or plan to use Noobs, better to have also:

• a HDMI monitor or a composite monitor (suggested an HDMI one)
• an USB keyboard
• an USB mouse

As keyboard and mouse, I used a wireless Logitech keyboard with an included touch-pad with USB dongle, in this way there is still available an USB Port.

SD card preparation  

Once all the HW components are available and connected, is possible to prepare the SD card.
Raspberry Pi does not have flash, it boots from the SD card that is used also as hard drive.
Because of that it needs to be formatted in Fat32.

Using kparted erase all the data on the SD card (new partition) and then simply format all the card in Fat32.
If you DON'T plan to use Noobs, there is no need to format the SD card.

Problems
Use a decent SD card for the job.
It should be fast and good quality/brand.
I had some SD cards not working properly because not fast enough or bad brand.
I found more reliable to use microSD cards with the adapter.

Installing distribution

There are two main choices about installing a distribution/OS on the SD card:

• installing Noobs
• installing a specific distribution

Noobs
If you choose to use Noobs, here some notes.
It is easier, shows you the latest available distributions and install automatically everything needed.
You must connect an HDMI monitor and a keyboard/mouse to the Raspberry Pi.

To install Noobs, simply download it and extract it on the SD card.
That's it. No strange formatting of the SD card, no partitions, secret code, ecc.
Just a plain copy.

Once copied, insert the card on the Raspberry Pi and turn it on.
After few seconds will appear on the HDMI screen the list of available OS to install.
If you have enough space on the SD card, it is possible to install more than one.

With 8Gbyte SD card, generally there is space for 1 or 2 OS.

The suggested distro to install is the Raspbian , accessible via the Noobs menu.

It is a Debian based distro and is probably the most used.
Once installed, a configuration menu' will allows to set up some parameters, like starting the distro in graphic mode rather than command line.
The default is command line ! So it is normal to boot in command line if no configuration modifications are made.

Raspbian
It is possible to install directly Raspbian. The main advantage is to have much more space on the SD card.
Here how to do it.
Go on the Raspberry Pi website download page , locate the Raspbian image and download it on your computer (look for Operating Systems Images - Raspbian).
Detailed explanations about how to do that are available on the Raspberry website, shortly here a quick reminder. I'm using Linux and I'm assuming you KNOW how to work on Linux.

• download the image on your PC
• extract the image from the zip file
• open a terminal
• df -h
  to see what memory devices are present
• insert the new SD card
• df -h
  identify the latest device inserted - ignore the partitions, we need to overwrite the entire card with the image
  If nothing appears, try with gparted or kparted to identify the new card
• umount /dev/sdxx
  umount the device added if for any reason it was mounted.
  In case the card has more than one partition, umount all of them.
  Eventually better reformat the card with gparted so to have a single partition but is not necessary.
• copy the entire image downloaded on the sd card with the command:
  
  dd bs=4M if=name_image_downloaded.img of=/dev/sdx
  
  where name_image_downloaded is the path/name of the downloaded Raspbian image and sdx is the name of the unmounted device (DEVICE !  NON PARTITION !)
  
  CAUTION!  Take your time and triple check ! If you use the wrong /dev you can lose your data !

At this point you have the SD card ready to be inserted in the Raspberry Pi.
Do it, be sure to have connected the board to the network, no need to have HDMI and keyboard/mouse, you can operate via ssh.

The image installed allows for the default user named 'pi' and password 'raspberry'.
Hook up  a terminal to the board, for example in ssh, is possible to login with:

- ssh pi@192.168.xxx.xxx   (address of the board - see your DHCP assignment)
- password : raspberry

Once gained access, is better to do an update with :  sudo apt-get update

After the reboot is better to configure Raspbian running the command sudo raspi-config.
At least run the option
- Expand Filesystem and the
- Advanced Options/A6 I2C in order to enable the I2C support.

No need to run other options.

The Raspberry Pi B (or B+) board is ready for the next step.

TeirmiLab - Designing a laboratory thermometer

Sometime is necessary to "reinvent the hot water".
In a  laboratory is necessary to measure the temperature of liquids and not always are easily available the last technological gadgets or practical one.

This article describes very generally some characteristics, requirements and usage of the gadget to design, a thermometer to be used in a laboratory

Important ! This project is based on specific requirements. Is not meant to be a "universal laboratory thermometer" but rather an instrument with specific characteristics needed in a specific laboratory.
The idea is that it can become a starting base for similar lab thermometers.

So here this project trying to design and build quickly a thermometer suitable to be used in a laboratory : the TeirmiLab

Lets start with the name.
The name is invented taking the first part of the Irish translation of "thermometer" (teirmiméadar) and of course "Lab" does not need of explanation.
Why Irish ? Well, I liked the sound of the name. The beauty of globalization.

The idea is to have a versatile and flexible instrument, capable to collect temperatures with probes attached to the display unit, measuring the current temperature, the minimum one, the maximum and work optionally as data logger.

The TeirmiLab can be also connected to a network (enhanced version), adding the possibility to see the current measurement in real time over a browser and adding graphic capabilities, remote setting of the unit and so on.

On the market do exists a lot of thermometers for laboratory use, but one of the goal of the project is to create an open platform and a thus customizable one, without spending up to thousand dollars.

The precision of the TeirmiLab initially is set as the sensor used, the DS1820. 

Requirements

The TeirmiLab should be able to performs these functions (the list has no particular priority)

Basic

• minimal and intuitive user interface
• read one sensor. The sensor should be detachable to be able to change it or clean it
• display the temperature away from the sensor
• display the temperature in Celsius or Farheneit or Kelvin
• Alarm
• Capability to offset the reading locally (setup)
• Capability to set the alarm locally

Enhanced

• read more than one sensor
• display locally the min and max temperature
• data logger capability
• capability to store locally temperatures for an amount of time
• setting for the measurement interval
• setting for start and stop
• capability to transfer the log to a remote computer
• remote connection capability
• setting alarms
• offsetting a probe
• download log
• reset log
• remote display capability
• (optional) print results locally
• (optional) RFID reader for identification 

Let see more in details some requirements for the basic version/

Minimal and intuitive user interface

In a world of "apps" it is easy to forget that sometime is more important a practical approach rather than a fancy one.
The user interface of the instrument is based on a "traditional" LCD display and few push-buttons.
No fancy touch screen with nice graphics.
A lab instrument needs to be first of all simple and immediate to use and sturdy, ANYBODY should be able to use it after 5 minutes and the tools itself must be capable to work in an hostile environments (spills, dirt, etc.)

Alarm

The TeirmiLab should have the capability to generate an alarm if a specific temperature is reached.
The alarm can be visual (change color of the display for example), audio (buzzer) or web based (browser pop up).

Remote display from the sensor

The sensor should be detached from the main unit, i.e. connected via cable.
The thermometer should be placed away (inches) from the source to measure so to easily locally display the temperature on a local display

Local settings

It must be possible to set locally some functionality, like setting an alarm or setting up an offset.
So a mini keyboard with at least three pushbutton is necessary.
Alternatively is possible to use a rotary digital  encoder with a pushbutton.

Keyboard/Keypad

Here a button requirements:

• Mode
  The Mode button allows to change the state of the instrument.
  There are 4 modes :
• Run  (default mode)
  In this mode the temperature read from the sensor is displayed in real time (every second).
  If the alarm is set, the display will show the normal temperature in Green and will switch in Red when the alarm is reached.
• Measurement unit
  By default the measurement unit is in Celsius.
  Alternatively is possible to select Fahrenheit or Kelvin
  The selection of the measurement unit automatically update the current values (alarm/offset)
• Alarm Set
  In this mode is possible to enter the alarm temperature, using other two pushbutton to increment or decrement such value
• Offset Set
  Some sensors can have an offset. This mode allows to add a value to the reading to offset the sensor.
• Increment
  The Increment button (+) allows to increment a value
• Decrement
  The Decrement button (-) allows to decrement a value

Digital Rotary Encoder

The pushbutton on the encode select the mode, then rotating the encoder clockwise will increase a value. Rotating the encoder counterclockwise will decrease a value.

• Mode
  The push button  allows to change the state of the instrument.
  There are 4 modes :
• Run  (default mode)
  In this mode the temperature read from the sensor is displayed in real time (every second).
  If the alarm is set, the display will show the normal temperature in Green and will switch in Red when the alarm is reached.
• Measurement unit
  By default the measurement unit is in Celsius.
  Alternatively is possible to select Fahrenheit or Kelvin
  The selection of the measurement unit automatically update the current values (alarm/offset).
  Rotating the encoder will change the selection
• Alarm Set
  In this mode is possible to enter the alarm temperature, rotate the encoder clockwise or counterclockwise to increase and decrease the alarm temperature
• Offset Set
  Some sensors can have an offset. This mode allows to add a value to the reading to offset the sensor.
• Reset
  This option reset the TeirmiLab in a known configuration
• Unit used : Celsius
• Alarm disabled
• Alarm value = 0
• Offset = 0
• Setting
  When in a specific mode, rotating the encoder clockwise or counterclockwise will change the selection.