(r8) SolutionsToTheExercises < Embedded

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---+ Solutions to the exercises

This is the page to which the solutions will be uploaded. These will mainly consist of gzipped tar files which you can download and unpack.

For the exercise on Linux the are no solutions as these are simple Linux commands to be executed into the bash command interpreter.<br /><br />
   * <b>Solutions to exercise 1: Linux Commands</b><br />There are no solutions to this exercise. We simply try out a series of bash commands<br /><br />
   * *Solutions to exercise 2*: __C__ <b>programming:</b><i><br /></i>These are only the solutions to the exercises. Many more small example programs you find in the lecture page <br />[[Lecture3: Introduction to C Programming]]
%ATTACHURL%/solEx2.tar.gz<br /><br />
   * <b>Solutions to exercise 3: Programming Tools</b><br />Even though there are no solutions to exercise3: _Compilations Tools_, here are a few Makefile examples nevertheless:
%ATTACHURL%/makeExamples.tar.gz

   * <b>Solutions to the exercises on files, pipes and sockets<br /></b>These exercises have been skipped but I attach the solution codes nevertheless such that you can have a look at them and/or use them in a future course
%ATTACHURL%/communication.tar.gz

   * <b>Solutions to exercise 4: Raspberry Pi<br /></b>There are no solutions to this exercise session because we only use programs that have already been written before.<br /><br />
   * <b>Solutions to exercise 5: LED<br /></b><br />For the mygpio program, these are the tests you must perform in order to make the program safe against wrong input from the user
      * test if the user has given at least 2 arguments namely a string, which should be "read" or "write" and the pin number<br />(argv may not be smaller than 3)
      * check if argv[1] is either "read" or "write". Use strcmp to accomplish this
      * if argv[1] is "read", make sure argc is exactly 3
      * if argv[1] is "write", make sure argc is exactly 4
      * convert the pin number from string to integer. You may be tempted to use atoi() but you must not, because atoi() does not check for conversion errors. Use strtol() instead.
      * Make sure the converted pin number is in the range 0..7<br />For the "read" case we are done with our checks here
      * for the "write" case convert the logic level and make sure you get either 0 or 1<br /><br />
%ATTACHURL%/leds.tar.gz<br /><br />
   * <b>Solutions to the exercises on switches</b><br /><br />These exercises have also been skipped because of lack of time but I attach the solution codes nevertheless such that you can have a look at them and/or use them in a future course

%ATTACHURL%/switches.tar.gz
<br /><br />
   * <b>Solutions to exercise 7: Stepping Motors<br /></b><br /><i>This one is for the lecturers only:</i><br />When working with pigpio via the pigpiod daemon, the daemon most first be started be the super user. <br />If you do not want to give root access to your students (which you probably don't want as long as they do not really know what they are doing) you may start the daemon at system startup:<br /><br />
      * Copy the pigpiod startup script ( %ATTACHURL%/pigpiod )to /etc/init.d
      * chmod 755 /etc/init.d/pigpiod
      * update-rc.d pigpiod defaults
      * update-rc.d pigpiod enable
After reboot pigpiod will be started automatically.<br /><br />In addition to the solutions to the stepping motor exercises I add the code written for the rotary encoder, which is a sort of a reverse stepping motor. Instead of sending a pulse sequence, you receive one and by interpreting it you can tell the relative angle the motor has reached. Here is the code:
%ATTACHURL%/rotaryEncoder.tar.gz<br /><br />
   * <b>Solutions to the exercises on the !DS18B20 1-wire digital temperature sensor<br /><br /></b>The solutions make use of the device driver available for the !DS18B20 in the Linux system. Since we had no time to look into the concepts of device drivers, this exercise has been left out. Here are the solutions, if you want to try for a future course:
%ATTACHURL%/ds18b20.tar.gz<br /><br />
   * <b>Solutions to exercise 6: The DHT11 temperature and humidity sensor<br /><br /></b>The code contains an example of how to write a shared library. You can collect all libraries for your course in a common directory (.g. /opt/ucc/lib) as you do for all corresponding include files (/opt/ucc/include). Then you make the directory of libraries globally known to the system by putting a file ucc.conf into /etc/ld.so.conf. ucc.conf simply contains the text _/opt/ucc/lib_. Finally you run the command <i>sudo ldconf </i>and _/opt/ucc/lib_ will be added to the search path of shared libraries on the system.<br /><br />
   * <b>Solutions to the exercises on light measurement<br /></b><br />Again the exercises have not been proposed during the course. They use the photo resistor available in the sensor kit but need a high value capacitor in addition. In these exercise the analogue value of resistance is not measured through an ADC but uses a capacitor which is charged over the resistance in the photo resistor. By measuring the time the capacitor needs to be charge to a level that switches the state of a gpio pin from low to high, the resistance and thus the light intensity can be measured.<br />Again the solutions are available here:
%ATTACHURL%/photoResistor.tar.gz<br /><br />
   * <b>Solutions to exercise 12: Reading the BMP180 temperature and barometric pressure sensor<br /><br /></b>The manufacturer of the device provides an access library to the device which takes care of converting the raw data read from the sensor device into humanly readable values. The library must be adapted to the I2C access method used be the micro-controller to which the device is connected (in our case the Raspberry Pi). The solutions show how this is done, how to extract the documentation from the source code using the _doxygen_ tool and how to use the library in your own programs.
%ATTACHURL%/bmp180.tar.gz<br /><br />
   * <b>Solutions to exercise 10: a 2 line LCD Display<br /><br /></b>Very often embedded systems do not have a keyboard, mouse and screen attached to them but they must live with more rudimentary (and much cheaper) input/output devices. Such a device is the 2-line display we have in our sensor collection. It is highly recommendable to write a shared library for the device because it can be used in many applications (see the !nameDisplay, !VoltMeter and !MeteoStation we had at the Open Day).<br /><br />The solutions show how this is done, how the library is tested and how to include in-code documentation in _doxygen_ format.<br /><br />
   * <b>Solutions to exercise 8: Digital to Analogue conversion</b><br /><br />Many devices are controlled through analogue signal levels. A nice example of a device creating these signal levels is the !MicroChip mcp4725, a 12 bit !I2C based DAC. The solutions show examples of how to set a level and how to create wave forms.<br />The frequency of the wave form is limited by the !I2C access speed (normally 100 kBit/s). The chip is capable of going up to 3.4 MBits/s, which however I have not tried. You would have to modify the bit rate in the driver. Up to you to find out how this is done<br /><br />Here are some screen shots taken from the Hantek 6022BE oscilloscope equipped with far from perfect software. This software is however able to read out some wave forms and display them.
| <img alt="sineWave.png" height="177" src="%ATTACHURL%/sineWave.png" title="sineWave.png" width="329" /> | <img alt="sawtooth.png" height="176" src="%ATTACHURL%/sawtooth.png" title="sawtooth.png" width="324" /> |
| <img alt="triangularWave.png" height="180" src="%ATTACHURL%/triangularWave.png" title="triangularWave.png" width="333" /> | <img alt="rectangularWave.png" height="176" src="%ATTACHURL%/rectangularWave.png" title="rectangularWave.png" width="326" /> |

   * <b>Solutions to exercise 11: Analogue to Digital Conversion<br /></b><br />Even more important than digital to analogue conversion is its counterpart: analogue to digital conversion (ADC). Even though we have a high precision 4 channel ADC in our kit of sensors (the ADS1115 16 bit ADC) we use the much simpler model: a PCF8591, 8 bit ADC, simply because the PCB on which this ADC is mounted, already contains a potentiometer, a photo resistor and a thermistor which which we can play.<br />When used in conjunction with the 2-line LCD display it is easy to create a simple volt meter.<br /><br />
   * <b>Solutions to exercise 13: the ds1307 Real Time Clock<br /><br /></b>These solutions show how to set the real time clock using a complex command line argument interface with getopt_long. Many of the Linux commands are implemented this way. The program, when called without parameters, shows the current date and time, with parameters it allows to set seconds, minutes, hours, day...<b> <br /><br /></b>
   * <b>Solutions to exercise 9: the at24c32 EEPROM<br /><br /></b>We have a little PCB with a ds1307 Real Time Clock and an at24c32 32kbit EEPROM on board. Both devices can be accessed through the I2C bus. These solutions show what needs to be done to read and write the EEPROM. Again the access routines are implemented in a shared library. In this code we do not use pigpio library calls for !I2C access but use the device driver implemented for the Linux kernel directly.
-- %USERSIG{UliRaich - 2017-10-14}%

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Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
gz	bmp180.tar.gz	r1	manage	244.1 K	2017-10-31 - 08:38	UnknownUser
gz	communication.tar.gz	r1	manage	0.1 K	2017-10-26 - 08:24	UnknownUser
gz	ds18b20.tar.gz	r1	manage	20.9 K	2017-10-31 - 08:10	UnknownUser
png	highspeedWave.png	r1	manage	103.2 K	2017-11-01 - 10:11	UnknownUser
gz	leds.tar.gz	r1	manage	6.3 K	2017-10-26 - 11:50	UnknownUser
gz	makeExamples.tar.gz	r1	manage	1.7 K	2017-10-14 - 12:59	UnknownUser
gz	photoResistor.tar.gz	r1	manage	699.2 K	2017-10-31 - 08:30	UnknownUser
EXT	pigpiod	r1	manage	3.2 K	2017-11-01 - 17:15	UnknownUser
png	rectangularWave.png	r1	manage	83.3 K	2017-11-01 - 10:11	UnknownUser
gz	rotaryEncoder.tar.gz	r1	manage	6.1 K	2017-10-26 - 11:53	UnknownUser
png	sawtooth.png	r1	manage	85.9 K	2017-11-01 - 10:11	UnknownUser
png	sineWave.png	r1	manage	87.1 K	2017-11-01 - 10:11	UnknownUser
gz	solEx2.tar.gz	r1	manage	798.9 K	2017-10-14 - 12:53	UnknownUser
gz	switches.tar.gz	r1	manage	0.1 K	2017-10-31 - 08:03	UnknownUser
png	triangularWave.png	r1	manage	87.6 K	2017-11-01 - 10:11	UnknownUser

Topic revision: r8 - 2017-11-01 - uli