TeirmiLab - Raspberry Pi prototype

This article describes the building of a TeirmiLab prototype based on a Raspberry Pi B board.
The goal using a Raspberry Pi is to have a machine that can be expanded later.

Shopping list

• Raspberry Pi B or Raspberry Pi B+ or Raspberry Pi A+
• RGB 16x2 LED display
• DS1820 (specifically this one)
• MCP23017 I2C GPIO expander
• I2C RTC clock (optional)

The idea is to use a traditional LCD display instead a more sophisticate touch screen display.
Mainly the reasons :

• is not expensive
• doesn't require to develop a graphic interface for it
• allows to focus on the purpose - to show a temperature
• can be easily placed inside a protective container (no touch capabilities)

Hardware

Here a initial schematic for the TeirmiLab-Pi.

The RTC clock module is actually necessary only for the enhanced version, for the data-log feature, however it will be tested also on the base version.
The idea is to use as much as possible "ready to use" modules, like the RGB display, the GPIO I2C expander and so on, in order to use already made code (see the Software section).

The encoder will be connected directly to the Raspberry GPIO as well as the interrupt signal from the MCP23017 (optional for now), in order to be able to detect faster changes from the keyboard.
The internal pullup resistors for the encoder will be enabled.

First tests on a breadboard

The second prototype on perforated board

The second prototype on perforated board

The second prototype with the keyboard and RPOf cable connected

The keyboard is working fine, however it would be better to have an easiest way to select an alarm or set up the offset.
A new version of the hardware will include a digital encoder to be used instead the keyboard (see below).

The prototype installed on a wooden platform for a more mechanical stability.
A monochromatic LCD is used instead an RGB one

The prototype installed on a wooden platform for a more mechanical stability.
The round PCB is hosting the RPOf to be piggy-bagged on a MSP430 Launchpad

The used board for the prototype is a Raspberry Pi B, however the final installation will use a Raspberry Pi A+ because the reduced dimensions and power usage.
A new interface board is under development.

GPIO Use

Here a table for the GPIO use :

Raspberry GPIO	MCP GPIO	Direction	Description
	GPA0	Output	LCD
	GPA1	Output	LCD
	GPA2	Output	LCD
	GPA3	Output	LCD
	GPA4	Output	LCD
	GPA5	Output	LCD
	GPA6	Output	LCD
	GPA7	Output	LCD
	GPB0	Output	LCD
	GPB1
	GPB2
	GPB3
	GPB4	Input	Keyboard 1
	GPB5	Input	Keyboard 2
	GPB6	Input	Keyboard 3
	GPB7	Input	Keyboard 4
GPIO4		Input/Output	1Wire protocol
GPIO17		Input	Shutdown input
GPIO18		Output	Shutdown feedback
GPIO22		Output	Buzzer
GPIO23		Input	Encoder A
GPIO24		Input	Encoder B
GPIO25		Input	Encoder switch

Sensor

With the sensor used (DS18B20) the TeirmiLab has these basic characteristics:

• Range -55 to 125°C (-67°F to +257°F)
• ±0.5°C Accuracy from -10°C to +85°C

Keyboard

The TeirmiLab-Pi needs to have at least 3 push buttons in order to do some settings.

• a Mode button
  Allows to select different modes, like "display temperature" or "Set alarm" or "Set offset"
• two + and - buttons
  Allows to increase or decrease a value, like the alarm temperature or the offset

Encoder

Instead of the keyboard, it is more easy to use a mechanical digital encoder with an embedded pushbutton for the selection.
The pushbutton acts as Mode button and rotating the encoder cause the values to change.

The video is showing the encoder operations

Power Supply

The instrument must be powered.
An USB wall wart, with at least 1 A, will be the power source for the Teirmilab.

A main switch will be necessary in order to correctly power up and power down  the instrument (see RPOf project)

Container

All the electronic will be placed in a transparent plastic box.
This will allow to reduce the drilling to the minimum, basically for the main power switch and eventually for some push buttons if not other means are used.
The display will remain totally protected but visible behind the clear plastic.

MSP430 - How to use mspdebug

When using the MSP430 under Linux, in order to load the compiled code with mspgcc, exists a
utility called mspdebug.

Installation

Mspdebug is not part of the MSPGCC toolchain, so it must be downloaded and prepared separatedly.
Also the final placement could end  not be in the toolchain path but on a more generic one.
Almost every distribution has it, so the easiest way to install it is from there.

Alternatively, is possible to download the code from the mspdebug web site, then be sure to have installed the necessary libraries.

In particular must be installed :

• libncurses5-dev
• zlibc
• zlib1g-dev
• libx11-dev
• libusb-dev
• libreadline5-dev (or libreadline6-dev for newver version of Ubuntu)

Then :

• $ tar xvfz mspdebug-version.tar.gz
• $ cd mspdebug-version
• $ make
• $ sudo make install

At the end of the process, the mspdebug program will be placed in /usr/local/bin directory.

LaunchPad - Use

Preliminary

I'm describing the operations to use mspdebug with the LaunchPad.
Connect the LaunchPad to the host USB
Verify that the interface is seen by the system (the entry to check is highlighted) using lsusb.

steve@Oliver3:~$ lsusb
Bus 008 Device 023: ID 0781:a7c1 SanDisk Corp.
Bus 008 Device 001: ID 0000:0000
Bus 007 Device 018: ID 0451:f432 Texas Instruments, Inc.
Bus 007 Device 016: ID 051d:0002 American Power Conversion Uninterruptible Power Supply
Bus 007 Device 015: ID 06cd:0121 Keyspan USA-19hs serial adapter
Bus 007 Device 014: ID 17d0:0116
Bus 007 Device 003: ID 0409:0058 NEC Corp. HighSpeed Hub
Bus 007 Device 001: ID 0000:0000
Bus 005 Device 002: ID 04a9:2206 Canon, Inc. CanoScan N650U/N656U
Bus 005 Device 001: ID 0000:0000
Bus 004 Device 002: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
Bus 004 Device 001: ID 0000:0000
Bus 003 Device 002: ID 138c:0001
Bus 003 Device 001: ID 0000:0000
Bus 002 Device 003: ID 0a81:0205 Chesen Electronics Corp. PS/2 Keyboard+Mouse Adapter
Bus 002 Device 001: ID 0000:0000
Bus 006 Device 001: ID 0000:0000
Bus 001 Device 001: ID 0000:0000
Unless enabling the USB to a specific user, you need to be superuser to run mspdebug.
The interface to use is called rf2500.

Here a session opened with my main host (Ubuntu 8.04 LTS) and LaunchPad :

steve@Oliver3:~$ sudo mspdebug rf2500
MSPDebug version 0.9 - debugging tool for MSP430 MCUs
Copyright (C) 2009, 2010 Daniel Beer < daniel@tortek.co.nz>
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Trying to open interface 1 on 018
Initializing FET...
FET protocol version is 30066536
Configured for Spy-Bi-Wire
Set Vcc: 3000 mV
Device ID: 0xf201
Device: MSP430F2013
Code memory starts at 0xf800

Available commands:
= erase hexout mw read run sym
cgraph gdb isearch opt regs set
dis help md prog reset step


At this point is possible to work on the target, erasing the memory, loading test code and running the debugger.

For example, just to load a program (ELF format) on the MSP430, simply digit from inside the mspdebug program :

prog name_program.elf

Debugger (manual)

Here a sequence of operations to debug the code manually, using the debugger.
It is assumed that the mspdebug program is launched from the directory containing the elf file to debug.
The bolded lines are the ones to digit.

Load the program to be debugged in the microcontroller (from mspdebug)
(mspdebug) prog name_program.elf
Start the remote (target) gdb
(mspdebug) gdb
Bound to port 2000. Now waiting for connection...

At this point open a new terminal and go to the directory where the source code and elf are.
The bolded lines are the ones to digit.

Start the debugger

$ msp430-gdb name_program.elf
GNU gdb 6.8
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=msp430"...
(gdb)

Attach the debugger to the target
(gdb) target remote localhost:2000
Remote debugging using localhost:2000
0x0000f800 in _reset_vector__ ()


At this point it is possible to debug the code using the gdb commands.

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.

Raspberry Pi - reading a DS18S20

One of the most common things for any embedded device is the capability to read temperatures.

Raspberry Pi doesn't has any ADC by default, so unless to hook one, the common way to read temperatures is via digital chips, like the DS 18S20.

The DS 18S20 is a 1-wire protocol chip-set from Dallas.
Fortunately somebody already wrote a bit banging support for the 1Wire protocol used by this chip-set , so it is only matter to connect the chip and enable some kernel modules to do so, at least in Raspbian (Wheezi).

I was able to duplicate the results described in the article RaspberryPI DS1820 without problems.
The example is based on a Perl script using the kernel services.

Here some my extra notes (I don't understand why so many people stopped to draw standard electronic schematics in favor of "cartoon" schematics).

Basic schematic to connect a DS1820 to the Raspberry Pi Gpio port.

Raspberry Pi GPIO pinout

DS1820 pinout

By default (as described in the article) the kernel module capable to handle the 1-Wire is disabled.
As first thing is necessary to enable it.

Open a terminal, then :

• sudo modprobe wire
• sudo modprobe w1-gpio  
• sudo modprobe w1-therm

After that, to test if the DS1820 is ready and connected correctly :

• cat /sys/bus/w1/devices/w1_bus_master1/w1_master_slave_count

The result should be the number of DS1820 connected.

To retrieve the serial number of the chip-sets :

• cat /sys/bus/w1/devices/w1_bus_master1/w1_master_slaves

This is the Perl script used to read a sensor, copied from the article of David Mills,  RaspberryPI DS1820 (read that article for more details and how to read two sensors).

#!/usr/bin/perl

$mods = `cat /proc/modules`; 

if ($mods =~ /w1_gpio/ && $mods =~ /w1_therm/) 

{ 

   print "w1 modules already loaded \n"; 

} 

else  

{ 

   print "loading w1 modules \n"; 

   $mod_gpio = `sudo modprobe w1-gpio`; 

   $mod_them = `sudo modprobe w1-therm`; 

} 

$sensor_temp = `cat /sys/bus/w1/devices/10-*/w1_slave 2>&1`; 

if ($sensor_temp !~ /No such file or directory/) 

{ 

   if ($sensor_temp !~ /NO/) 

   { 

      $sensor_temp =~ /t=(\d+)/i; 

      $tempreature = (($1/1000)-6); # My sensor seems to read about 6 degrees high, so quick fudge to fix value  

      print "rPI temp = $tempreature\n";  

      exit; 

   } 

   die "Error locating sensor file or sensor CRC was invalid";  

}

Build an airflow sensor

For one of the projects I want/need to do, it was necessary to measure an airflow.
Here how I built a small sensor for that.

The simplest way to do so is to modify a computer fan.
I choose a small brush-less fan (for CPU), with ball bearings.

Circuit

Probably the simplest and safest way to detect the rotation of the blade, is to use an Hall Effect sensor.
The sensor is placed inside the fan case, instead of the original motor circuit.
Below the bipolar Hall Effect sensor I used.  No really need to have a bi-polar Hall Effect, actually a single pole Hall Effect it would work better, but this is what I had around at the time.

Hardware preparation

The first step was to split the rotor from the  main case.
Usually there is a small groove that keep the rotor in place.
On the rotor, in this type of fan, there is the permanent magnet.
It need to be removed.

The motor is usually soldered to a PCB,  just stuck in the plastic case.
With some force is possible to disconnect it.
3 wires, as the original configuration of the fan, are required for the Hall sensor.
Vdd, GND and the output.

Here some pictures of the conversion, starting from the original CPU fan I used (below)

The first thing was to take it apart, removing the motor and electronic.

 Then I glued an Hall Effect sensor close to the shaft, on the base.

On the propeller, I attached two earth rare magnets (very small and very powerful), on the opposite sides.
I left the metal rim inside to facilitate the magnet attach (I also glued them) and to give a little bit weight to the propeller.

The magnets are attached with the poles in the opposite direction, because the Hall Effect sensor I used is a bipolar one, i.e. it needs to "see" a North/South pole change in order to go on, and a South/North pole change to go off.

Here the anemometer completed, attached to a simple circuit to test the Hall Effect sensor.

In the last picture, it is possible to see also the 1 wire temperature sensor  (DS18S20) connected to the cable.
It is the sensor needed to detect the temperature of the air flow.
A simple first prototype , using an MSP430-2013, it was built to develop and test the firmware to read the anemometer and the temperature sensor.

Lawn mower - noise and pollution

In the article about the repair of my lawn mower, I mentioned that I can not stand the noise and pollution generated by a traditional gasoline lawn mower.
This article wants to explore little bit more the Pro and Cons to own a cordless (battery operated) electric lawn mower, using material available on the net and my personal experience
And yes, I'm biased toward electric ones for many reasons.

Let's start with a list of the Pro and Cons to choose an electric cordless lawn mower.

Pro

• is not generating ANY pollution
• is much less noisy
• it requires much less maintenance
• it is more safe

Cons

• it cost more
• it has a more limited cutting range
• it can be stopped more easily
• it is heavier

Let's discuss the Cons first.

Cost

The cost ... yes, a battery operated lawn mower could cost  more than an gasoline equivalent.
How much more ?

About 1-3 times more on average, BUT things are changing. Newer model of electric lawn mower are coming out with a decent price considered the features.
New type of batteries are used, improving the power and time, more efficient and powerful engines are used and a better blade design is adopted.
For example this new Craftsman 40V Lithium lawn mower has really impressive features considered the price.
My lawn mower is 4 years old. In 4 years the technology improved A LOT !
The future is electric !

Limited range

True with older models, unless to adopt very expensive batteries, a battery operated lawn mower can cut less yard than a gasoline one can do.

On average, a battery charge can last for about 20/30 minutes, assuming to have new/fresh batteries.
If you can cut the lawn on that time you are OK, otherwise you need to recharge it in the middle.
Again the technological improvement in this area is impressive.
Newer type of batteries allows to to extend  the cutting time.

Power

Usually a cordless electric lawn mower is less powerful than a gasoline one.

It can be quite a long and complicate discussion, but it is safe to say that a gasoline lawn mower is usually more powerful. This doesn't means that is a good thing.
Gasoline lawn mower simply use more power to overcame a poor design. More power means more gasoline used and thus more pollution and noise.

In the end the main reason to have more power is when the grass is too thick or too wet.
Blocks of accumulate grass can stop the blade.
The typical answer of a gasoline lawn mower is to increase the power, electric ones are better designed  to reduce the clogging and thus requiring less power.

Weight

The weight of an electric cordless lawn mower can be bigger than a gasoline one.

Up to 80 pounds on older models like mine. The batteries are the main component that determine the weight.

Traditional (and cheap) batteries usually weight a lot. Newer type of batteries are more powerful and last longer (both as life than discharge time).
The weight can be cut in half with newer batteries.

Let's see the Pro now.

Pollution

Well .. this is a BIG issue.
VERY big.
There is a lot to say about this, but let me start with the usual sentence many people say when talking about an electric mower and pollution : "yes, it does not pollute but the electricity you use is produced by plants that pollute !".

Who use this argument should be jailed.

Few points to consider:

1. Electricity is produced by many different type of plants, some pollute, others not.
   I can even set up a solar charger !
2. It is much easier and economic to apply filters to ONE plant than to million of machines
3. Gasoline mowers pollute directly AND indirectly, because in order to produce the gasoline ALL passages generate pollution, from the extraction to the transportation to the local gasoline station !!!
   Is much much more than the pollution created producing electricity.

But "how much" a gasoline lawn mower pollute ?
Well, the answer is really depressing.

Studies showed that the 5% of the USA national pollution is generated by lawn mower !

Each weekend, about 54 million Americans mow their lawns, using 800 million gallons of gas per year and producing tons of air pollutants.

(source http://www.peoplepoweredmachines.com/faq-environment.htm)

800 million gallons of gas per year !

Just to cut grass ???  

There are many studies out there that points out how much pollution is generated by these small appliances (for example http://abcnews.go.com/Technology/story?id=98532).

So much pollution just to have a nice and clean lawn. It is an oxymoron.

And the pollution is not limited to the gasoline burned.
Exists also the pollution created when oil and gasoline are "poured", during the  refilling of the mower. These are pollutant that are going directly in the lawn !

The only pollution that can come from a battery lawn mower are the batteries IF you throw them in the landfill.
For that reason I insist on the need to recycle the batteries !

I use a recycling service company for the batteries : Battery Solution
I usually buy a "iRecycle  kit" for household.
I can not stress enough the NEED to recycle batteries instead than trash them away !
From the button batteries to the sealed batteries, it is IMPORTANT to recycle them.
Don't throw them away !

Noise

A typical lawn mower with a gasoline engine, produce around 88-94 dBA of noise (source the NPC website).
Others sources bring the average lawn mower noise pollution around 90-106 dBA.
Over the 80 dBA the noise is considered unhealthy.

Just to have an idea, take a look to this loudness comparison chart (http://www.dot.ca.gov/dist2/projects/sixer/loud.pdf)

My electric lawn mower is not "silent" but is far lower noisy than the normal gasoline ones.

At 3 feet of distance, I measured 79 dBA.

Measurements done on neighbors lawn mowers at 10 feet (I could not go there and ask "Excuse me, can I measure your noisy piece of junk ? :) ), returned values of 86 dBA!!.

Here a list of measurements done:

• Craftsman at 3 feet, in front, on concrete (driveway) : 81 dBA
• Craftsman at 3 feet, in front, on grass : 79 dBA
• Craftsman at 10 feet, in front, on concrete : 68 dBA
• Neighbor lawn mower (unknown brand), on front, approx 10 feet (probably more) : 86 dBA 

Just let say that I cut the grass at the same time of my neighbor, and I was barely hearing MY lawn mower !!!

The noise from the neighbor lawn mower, at the other side of the road, was COVERING the noise of my lawn mower, and I was just behind it !

Need more proofs ?

Maintenance

An electric mower has basically 3 components :

• Batteries
• Control/wiring
• Motor

The only component that wear out are the batteries, so it is the only thing to maintain.
Every few years a new set of batteries need to be installed.

Other than that, no gasoline and oil.

A typical gasoline engine has more than 100 parts that can break down. An electric motor has two.

Safety

Gasoline is extremely dangerous.

It can catch fire easily, vapors are harmful, oil is extremely pollutant.

The two technologies (gasoline/electric) have HUGE differences in safety and the most safe is not the gasoline.
The only risk with an electric mower is an unexpected closing of the circuit, reason why usually exists a double switch.
On mine for example, a physical "key" need to be inserted in the control box, where there is the main switch.
Without the key, the switch is disabled.