An Introduction to Using the Gertboard with the Raspberry Pi

1. Overview
2. System Configuration
3. Bill of Materials
   • System Configuration
   • Hardware Configuration
   • Software Configuration
4. Set of Instructions
5. More Details
   • Configure the R-Pi System
   • Connecting the Gertboard
   • Using the Gertboard Buffered Output
   • Using the Gertboard ADC Channels
   • Using the Gertboard Buffered Input
6. Using the Gertboard
   • Wiring-up the Hardware
   • Demonstrating the Gertboard Buffered Output (LEDs)
   • Demonstrating the Gertboard Analogue to Digital Converters (Potentiometer)
   • Demonstrating the Gertboard Buffered Input (Buttons/Switches)
7. Trouble Shooting
8. Appendix A - The Gertboard
   • A1 The Gertboard Layout
   • A2 The Gertboard Buffered Output Configuration
   • A3 The Gertboard ADC Channel Configuration
   • A4 The Gertboard Buffered Input Configuration
9. Appendix B - The Software
   • B1 System Software
   • B2 The Standard Gertboard Control Software
   • B3 Web-based Gertboard Control Software
10. Appendix C - The External Interface Board
    • C1 The Board Layout
    • C2 The LEDs
    • C3 The Switches
    • C4 The Potentiometer
11. Terminology
12. About this Document

Overview

This Project is about introducing the use of the Gertboard to extend the functionality of the Raspberry Pi (R-Pi). In particular, the use of the Gertboard to drive external Light Emitting Diodes (LEDs), to provide input from external switches/buttons and to use the Analogue to Digital Converters (ADC) will be explained and demonstrated. Furthermore, the control of the Gertboard directly from the R-Pi and its keyboard/mouse, and from a browser through a network will also be explained and demonstrated. The key learning objectives of this project are for an intermediate/novice developer to learn:

• How to use the LED, push-button switch and ADC features on a Gertboard connected to a R-Pi and how to use the Gertboard to control external LEDs and push-button switches;
• How to write software that can be used by any browser-enable device e.g. smart phone, tablet, desktop, etc. to access the LEDs, push-button switches and ADCs controlled by the Gertboard.

The associated Bill of Materials describes the set of components, hardware and software, required to complete this project. When complete, the system will look as shown in the Figure below. There is a signifiant amount of information about the Gertboard available on the Element14 Community Gertboard web-site.

The completed system.

1. System Configuration

The system configuration is shown in Figure 1.1. The basic configuration is:

• R-Pi (Model A/B) - this project can make use of either Model. In both cases it is recommended that a WiPi is used to provide network connectivity (wireless, IEEE 802.11) via the USB2 port on the R-Pi. Network connectivity is required to provide access to the R-Pi Web Server and to download and install the necessary software updates required by the Gertboard software. A USB2 hub is recommended to enable more than two USB devices to be linked to the R-Pi (the R-Pi has two USB ports). It is assumed that the keyboard and mouse are linked via the USB Hub. The monitor can be linked either via the HDMI interface or the yellow RCA phono connector for composite video output. In this project a PiView connector is used to enable a monitor with a VGA connector to be connected to the R-Pi via the HDMI interface;
• Gertboard - a single Gertboard is connected to the GPIO interface on the R-Pi. The Gertboard configurations vary depending on the input/output operations required. For this set of instructions the Gertboard will be configured, separately, to drive the internal/external Light Emitting Diodes (LEDs), the internal/external switches/buttons and the external potentiometer. The Gertboard User Manual (Revision 2.0 published in 2012 by Fen Logic Ltd) is available at: Gertboard User Manual. This is required reading;
• LEDs, Switches and Potentiometer (Pot) circuitry - the 12 LEDS are wired so that they can be driven as outputs via the Gertboard buffers. The LEDs used in this project have forward voltage of between 2.0V-2.2V.  The two external switches are 'Push-to-Make' switches and they are again connected to the Gertboard buffers. The 'Pot' is wired to the Analogue-to-Digital Converter (ADC) interface on the Gertboard.

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When the complete system is built it will look as shown in Figure 1.2.  The views shown in Figure 1.2 are front (a), back (b), and sides (c) and (d).

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2. Bill of Materials

2.1 System Configuration

The architecture is based upon the use of an R-Pi to drive a Gertboard with the software controlled by access through a web browser. The configuration is shown in Figure 2.1 and the key to the alphanumeric labels is provided in Tables 2.1 and 2.2.

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The associated bill of materials for the system shown in Figure 2.1 is listed in Table 2.1.

Table 2.1 - The Bill of Materials.

2.2 Hardware Configuration

The hardware connectivity is detailed in Table 2.2.

Table 2.2 - Hardware connectivity.

2.3 Software Configuration

The software required to support this project that must be installed on the R-Pi is:

• R-Pi Operating System (Raspbian) - this is installed using the NOOBS that comes pre-installed on the R-Pi SD cards.  If NOOBS is not preinstalled it is available at Downloads;
• Integrated Development Environment - IDLE with Python 2.x support (normally installed as part of Raspbian);
• The Apache2 Web Server - this may be installed as part of the Raspbian operating system. If not, then use the instructions provided in Appendix B1.5.

3. Set of Instructions

The set of instructions for using the Gertboard are:

1. Configure the R-Pi system in preparation for the connection of the Gertboard and usage of the software i.e. the monitor, USB2 Hub, keyboard and mouse and the network connection (using either a WiPi for wireless access or using the wired Ethernet port).  If the WiPi is to be used then insert the WiPi into one of the USB ports on the R-Pi - see More Detail;
2. The next step is to connect the Gertboard to the RPi.  The Gertboard/RPi connection is via the GPIO interface on the top of the RPi and the underside of the Gertboard (the layout of the Gertboard is shown in Appendix A). The Gertboard is supplied with a set of 6 plastic rods that can be inserted into the Gertboard so that it can be stood without the underside of the board touching the surface and so that the GPIO interface does not take all of the weight of the Gertboard on the RPi.  If the Gertboard is to be inserted directly into the RPi then do not insert the plastic rod on the bottom left corner of the Gertboard when looking at the underside with the GPIO connector at the bottom (this corner rests over the video jack port). It is possible to use a extra GPIO male/female cable (not supplied as part of the Gertboard) to connect the Gertboard to the RPi but in these instructions direct connection is assumed - see More Detail;
3. The external interface board that provides the external LEDs, switches and the potentiometer can now be constructed. The exact layout of the board is unimportant and fewer LEDs and/or switches can be used. The layout of the Board used in these instructions is described in Appendix C and in Video 1. This board will be used to show how the Gertboard is used to drive external devices through the ADC and Buffered I/O pins on the Gertboard;
4. The Buffered Output on the Gertboard can now be demonstrated. This is demonstrated by using the R-Pi to switch on and off the set of onboard LEDs (on the Gertboard) and external LEDs (on the external interface board). The first demonstration will use the test software that is available as part of the Gertboard distribution kit.  This test software is available as both 'C' and Python code. We will use the Python versions only. The instructions to obtain the Python text software are given in Appendix A2. The Gertboard must be wired for buffered output using the appropriate wiring straps and jumpers (if all twelve LEDs are to be used then 12 jumpers are placed on the Gertboard, 12 wiring straps are used on the Gertboard between the GPIO pins and the B1-B12 pins, and 24 wiring straps are used between the buffer pins and the LED pins and the external interface board - see Video 2). The test program 'leds-rg.py' is now used (this is a part of the downloaded Gertboard test software) to demonstrate the LEDs being switched on and off (see Video 3) - see More Detail;
5. Driving the Buffered Output on the Gertboard via a web browser can now be demonstrated. The hardware configuration and wiring of the R-Pi and Gertboard remain unchanged. The software configuration must be changed. New Python software is available that enables the same set of LEDs to be controlled using a web browser.  This software includes an HTML page which is loaded into the web browser to enable the control of the LEDs. Any web browser can be used on any device that supports a web browser.  We demonstrate the use of an iPad with the Safari web browser but the software has also been tested using Midori on the R-Pi and a Chrome, Safari and FireFox on a range of other devices (see Video 3) - see More Detail;
6. The ADC on the Gertboard can now be demonstrated. This is demonstrated by using a potentiometer to provide a variable analogue input to the Gertboard's ADC input ports. The equivalent digital value is then provided by the Gertboard's ADC. The first demonstration will again use the Python test software that is available as part of the Gertboard distribution kit. The Gertboard must be wired for one of the ADC channels (the Gertboard has two ADC channels) using the appropriate wiring straps and jumpers i.e. four jumpers and three wiring straps between the ADC pins and the potentiometer on the external interface port (see Video 4). The test program 'atod.py' is now used to show the digital output when the value of the potentiometer is manually varied (see Video 4) - see More Detail;
7. Monitoring the use of the Gertboard's ADC via a web browser can now be demonstrated. Again hardware configuration and wiring of the R-Pi and Gertboard remain unchanged. Also, new Python software is available that enables the ADC channels to be monitored using a web browser (see Video 4). This software includes an HTML page which is loaded into the web browser. Any web browser can be used on any device that supports a web browser - see More Detail;
8. The Buffered Input on the Gertboard can now be demonstrated. This is demonstrated by using the three onboard switches (on the Gertboard) and two external switches (on the external interface board). The first demonstration will again use the Python test software that is available as part of the Gertboard distribution kit. The configuration and wiring (using the appropriate jumpers and wiring straps) of the Gertboard is different for the onboard and external switch usage (see Video 5). The test program 'buttons-rg.py' is now used to demonstrate the operation of the buffered input ports via the switches (see Video 5) - see More Detail;
9. Monitoring the Buffered Input on the Gertboard via a web browser can now be demonstrated. The hardware configuration and wiring of the R-Pi and Gertboard remain unchanged. Again new Python software is available that enables the buffered inputs to be monitored using a web browser (see Video 5).  This software includes an HTML page which is loaded into the web browser - see More Detail.

4. More Details

4.1 Configure the R-Pi System

The layout of the R-Pi (Model B) is shown in Figure 4.1. Once the various cables have been connected to the R-Pi, the configuration is as shown in Figure 4.2 (the alphanumeric annotations refer to the identifier entries in Tables 2.1 and 2.2). The latest versions of the Raspbian operating system can be installed using the instructions in Appendix B1.1. Make sure that the Git client is installed (see Appendix B1.2).

Figure 4.1 - R-Pi Model board B layout.	Figure 4.2 - The R-Pi with the set of connected cables.

If the WiPi has been inserted, the use of the appropriate wireless network must be established (this requires a wireless network to be activated, via an appropriate wireless network access device e.g. a wireless router, and for that device to be assigning IP addresses using DHCP). This is achieved by working on the desktop:

1. Click on the 'wifi config' icon;
2. Now click on the 'scan' button;
3. From the resulting scanned list pick your wireless network;
4. Enter the password for the network in the 'psk' box and click 'Add';
5. Click 'Connect'. The wireless network access point will now allocate an IP address to the R-Pi and will display the IP address (for example this will take the form of 192.168.1.99). Make a note of this address as this value will be required in some of the later instructions;
6. Test that there is network access by running the Midori web browser to access a web-site e.g. the BBC web-site at: http://www.bbc.co.uk.

Once the above WiPi configuration has been completed, the R-Pi can be rebooted without repeating the above actions. However, each time the R-Pi is rebooted, the DHCP may not allocate the same IP address. In this case the IP address can be obtained by:

1. Click on the 'LXTerminal' icon;
2. Type the instruction: Hostname -I

The same approach for obtaining the IP address is used if the Ethernet port on the R-Pi Model B is being used.

4.2 Connecting the Gertboard

The Gertboard and the R-Pi are connected via the GPIO connectors. The GPIO interface on the underside of the Gertboard (female) is inserted into the GPIO interface (male) on the R-Pi. Figure 4.3 shows the resulting layout. If the 'Missing' Stand Pin was not missing then this form of connection would NOT be possible and so a separate cable would be required.

Figure 4.3 - Connecting the Gertboard to the R-Pi.

Once the Gertboard and the R-Pi have been connected then various software should be installed (the installation of the software does not require the Gertboard to be connected to the R-Pi). The software to be installed is:

1. The WiringPi Python module - see Appendix B1.3;
2. The SPI Dev module - see Appendix B1.4;
3. The Apache2 Web Server - see Appendix B1.5;
4. The standard Gertboard control/demonstration software (from Raspi TV) - see Appendix B2;
5. The new Gertboard Web Server-based control/demonstration software (from the Element14 Github) - see Appendix B3.

4.3 Using the Gertboard Buffered Output

The wiring of the RPi, Gertboard and the LEDs on the external interface board is shown in Figures 4.4 and 4.5 (note that in the associated videos there drop-down resistors have been removed as these were significantly reducing the LED brightness). The full details of the actual wiring of the Gertboard to use the buffered output is described in Appendix A2 and shown in Video 2. In Figures 4.4 and 4.5. all 12 buffered outputs are being used to drive the external LEDs and in this configuration the state of the external LEDs must always be same as the same as the internal LEDs. Due to the wiring on the external interface board the the wire straps to the equivalent buffered input/output pins on the Gertboard are swapped (this can be avoided by changing the wiring between the external LEDs and the 2-pin headers). The use of the buffered output ports can now be demonstrated using the standards test Python program in the file 'leds-rg.py' or 'leds-wp.py': the details for obtaining this software are given in Appendix B2. See Video 3 for a demonstration of the control of the onboard and external LEDs.

Figure 4.4 - R-Pi/Gertboard wiring for using the buffered output ports (top view).

Figure 4.5 - R-Pi/Gertboard wiring for using the buffered output ports (side view).

The equivalent browser-based software can now be used. The details for obtaining the software are given in Appendix B3. The R-Pi and its Apache Web Server (make sure that Apache2 is active on the R-Pi- see Appendix B1.5) must be on a network for this approach to work (in Figure 4.4 the network access is supplied using the WiPi). Once the Web Server Python demonstration software has been installed, a Web browser is used to access the web-page: this requires the IP address of the R-Pi to be used as part of the URL for the web page.  i.e.

     http://<Your IP Address>/GertBoardTestv1p0p0.html

Using this Web Page the state of the onboard and external LEDs can be controlled (press the blue button on the web-page). See Video 3 for a demonstration of the Web Server approach for driving the onboard and external LEDs.

4.4 Using the Gertboard ADC Channels

The wiring of the R-Pi, Gertboard and potentiometer on the external interface board is shown in Figure 4.6 (the wiper pin on the potentiometer, the central pin, is connected to the AD0 pin on the Gertboard using the yellow wire). The full details of the actual wiring for a potentiometer is described in Appendix A3. In this demonstration only one potentiometer is wired to the Gertboard using ADC channel 0. The use of the potentiometer can now be demonstrated using the standards test Python program in the file 'atod.py': the details for obtaining this software are given in Appendix B2 and this requires the 'py-spdev.py' module and SPI configuration as described in Appendix B1.4. See Video 4 for a demonstration of the expected output on the screen as the potentiometer is rotated.

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Again the equivalent browser-based software can now be used. The details for obtaining the software are given in Appendix B3. The R-Pi and its Apache Web Server (make sure that Apache2 is active on the R-Pi- see Appendix B1.5) must be on a network for this approach to work (in Figure 4.6 the network access is supplied using the WiPi). Once the Web Server Python demonstration software has been installed, a Web browser is used to access the web-page. Using this Web Page the variation of the potentiometer can be displayed (press the red button on the web-page). Note that unlike the standard test program which uses a continual poll of the ADC values, the Web Server approach is a single poll after a period of some 5 seconds (this period can be altered by editing the Python code). See Video 4 for a demonstration of the Web Server approach for monitoring the potentiometer.

4.5 Using the Gertboard Buffered Input

The wiring of the RPi, Gertboard and the switches on the external interface board is shown in Figures 4.7, 4.8 and 4.9. The full details of the actual wiring of the Gertboard to use the buffered output is described in Appendix A4 and shown in Video 5. The wiring for using only the three onboard switches is shown in Figure 4.7. When support for two external switches is added then the wiring in Figure 4.8 is used (the two external switches are connected using the 'B11-B12' buffered input/output ports and jumpers must be placed on the 'B11-B12' In jumpers i.e. to set the 'B11-B12' input/output ports as input. The use of the buffered output ports can now be demonstrated using the standards test Python program in the file 'buttons-rg.py' or 'buttons-wp.py': the details for obtaining this software are given in Appendix B2. See Video 5 for a demonstration of the onboard and external switches/buttons (note that in the Video the external switches are wired to the 'B1-B2'  buffered input/output ports so that the same test software that is used to demonstrate the onboard buttons can be used for the external switches).

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Again the equivalent browser-based software can now be used. The details for obtaining the software are given in Appendix B3. The R-Pi and its Apache Web Server (make sure that Apache2 is active on the R-Pi- see Appendix B1.5) must be on a network for this approach to work (in Figures 4.7, 4.8 and 4.9 the network access is supplied using the WiPi). Once the Web Server Python demonstration software has been installed, a Web browser is used to access the web-page. Using this Web Page the variation of the state of the switches/buttons can be displayed (press the green button on the web-page). Note that unlike the standards test program which uses a continual poll of the switch/button values, the Web Server approach is a single poll after a period of some 5 seconds (this period can be altered by editing the Python code). See Video 5 for a demonstration of the Web Server approach for monitoring the state of the switches.

5. Using the Gertboard

5.1 Wiring-up the Hardware

A video, 6 minutes long, demonstrating the wiring of the Gertboard and R-Pi is shown in Video 1. This video is available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view.

Video 1 - Wiring the Gertboard, R-Pi and external interface board.
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5.2 Demonstrating Gertboard Buffered Output (LEDs)

A video, 6 minutes long, demonstrating the wiring of the external LEDs to the Gertboard's buffered output is shown in Video 2. This video is available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view.

Video 2 - Wiring the buffered output on the Gertboard.
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A video, 3 minutes long, demonstrating the use of the Gertboard with external LEDs is shown in Video 3. This video is available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view.

Video 3 - Demonstrating the buffered output on the Gertboard.
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5.3 Demonstrating the Gertboard Analogue to Digital Converters (Potentiometer)

A video, 5 minutes long, demonstrating the wiring of the Gertboard to the potentiometer using the ADC is shown in Video 4. This video is available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view.

Video 4 - Demonstrating the ADC on the Gertboard.
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5.4 Demonstrating the Gertboard Buffered Input (Buttons/Switches)

A video, 8 minutes long, demonstrating the use of the Gertboard's buffered input using external switches and R-Pi is shown in Video 5. This video is available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view.

Video 5 - Demonstrating the buffered input on the Gertboard.
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6. Trouble Shooting

Appendix A - The Gertboard

A1 The Gertboard Layout

The layout of the Gertboard is shown in Figures A1.1a (top view), A1b (top view with detailed jumper pins layout) and A1.1c (underside view). The top view shows the location of the GPIO pins, the buffed input/output pins, the onboard LEDs, the ADC pins, the 3.3V power pins and the three onboard switches. The Gertboard provides 12 buffer ports that can be configures for either Input or Output (see Figure A1.1a) and these have a set of LEDs that also show the status of the signal level on the port. The buffer ports are configured as either Input or Output ports using the three sets of input jumper pins (the 'B1..B4', 'B5..B8' and 'B9..B12' In-Jumper pins) and the three sets of output jumper pins (the 'B1..B4', 'B5..B8' and 'B9..B12' Out-Jumper pins) - see Figure A1.1b. Jumpers are placed cross the relevant pins to set the configuration.  The buffered ports are linked to the corresponding GPIO ports, and hence the R-PI, using wiring straps between the twelve GPIO Pins (Figure A1.1a) and the twelve 'B1..B12' In/Out Port Pins (see Figure A1.1b).

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The Gertboard is supplied with a set of 6 plastic rods that can be inserted into the Gertboard so that it can stand without the underside of the board touching the surface and so that the GPIO interface does not take all of the weight of the Gertboard on the RPi.  If the Gertboard is to be inserted directly into the RPi then do not insert the plastic rod on the bottom left corner of the Gertboard when looking at the underside with the GPIO connector at the bottom (this corner rests over the video jack port).

A2 The Gertboard Buffered Output Configuration

The wiring of the Gertboard for use with the buffered output functions is shown in Figures A2.1a (top view) and A2.1b (schematic top view): the schematic view is taken form the Gertboard User Manual and amended to include the wiring to the external devices e.g. LEDs. The wiring uses 12 jumpers on the B1-B12 Out jumper pins sets i.e. three blocks of four jumpers. Twelve, short, wiring straps are used to link the GPIO pins to the 'B1-B12' In/Out port pins (these set the buffered ports as outputs i.e. a signal is sent as output from the R-PI).  Finally, 24, long, wiring straps are used to connect the 12 external LEDs to the buffered I/O ports.

Further side views of the Gertboard wiring for the use of the buffered output ports are shown in Figure A2.2.

A3 The Gertboard ADC Channel Configuration

The wiring of the Gertboard for use with the ADC functions is shown in Figures A3.1a (top view) and A3.1b (schematic top view): the schematic view is taken form the Gertboard User Manual. This wiring is for the use of the ADC0 channel only. The wiring uses four Jumpers on between the pins GP11-SCLK, GP10-MOSI, GP9-MISO and GP8-CSnA). Three wiring straps are used: Black to the 3.3V pin (line 3 in Figure A3.1b), Red to the GND pin (line 1 in Figure A3.1b) and Yellow to the ADC pin (line 2 in Figure A3,1b). It is the Yellow wire that must be connected to the wiper on the potentiometer. The connection of the Red and Black wires to the potentiometer determines the direction in which movement changes, increasing/decreasing, the resistance.

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Further views of the wiring of the Gertboard for use with ADC Channel 0 are shown in Figures A3.2 (the same wiring as shown in Figure A3.1). Figure A3.2a shows connection to a potentiometer with the Yellow cable connected to the wiper (central pin) of the potentiometer.

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A4 The Gertboard Buffered Input Configuration

The wiring of the Gertboard for use with the onboard buttons and buffered input functions is shown in Figures A4.1a (top view) and A4.1b (schematic top view): the schematic view is taken form the Gertboard User Manual and amended to include the wiring to the external devices e.g. buttons. In Figure A4.1b the wiring uses 5 jumpers on the B1-B3 Out jumper pins sets and the B11-B12 In jumper pins. Five, short, wiring straps are used to link the GPIO pins to the 'B1-B3' (these are optional) and 'B11-B12'  (to set these as input ports) In/Out port pins. Finally, 4, long, wiring straps are used to connect the two external buttons to the buffered I/O ports.

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Further side views of the Gertboard wiring for the use of the onboard switches are shown in Figure A4.2.

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Appendix B - The Software

B1 System Software

B1.1 Update the Operating System

To ensure that you have the latest version of the operating system and the Python development environment then working in the LXTerminal application type the following instructions:

     sudo apt-get update

     sudo apt-get install python-get python-pip

This will download and install the latest versions of the software.

B1.2 Install GIT

A lot of the required software is stored in GitHub.  Access to this software repository requires the use of Git. To install Git, use the LXTerminal and type the following instructions:

     sudo apt-get install git-core

The installation process will inform you if you already have the latest version of Git installed and will to over right that latest version.

B1.3 Install the Wiring.Pi Module

Using the LXTerminal application type the following instruction:

     sudo clone git://git.drogon.net/wiringPi

To build and install the WiringPi module type:

     cd wiringPi

     sudo ./build

Once this installation has been completed it can be confirmed by typing the instruction:

     gpio -v

This should print to the terminal a list of the states of all the GPIO devices. This list provides a map between the WiringPi Pin Number, the BCM (Broadcom chip) GPIO Pin Number, Physical Pin Number, Mode and Value.  Take a copy of this table.

NOTE: If you use the GPIO Utility then be careful because some functions use the 'BCM Pin Number' whereas others use the 'WiringPi Pin Number' by default.  Read the GPIO Utility notes carefully.

B1.4 Install and Enable the SPI Dev Module

Using the LXTerminal application, the 'py-spidev' module is installed by typing the following instructions (make sure that Git has been installed):

     cd ~

     git clone git://github.com/doceme/py-spidev

Once completed, type:

     cd py-spidev

     sudo python setup.py install

Once the module has been installed, the SPI capability for the operating system must be enabled. To enable the SPI driver the file raspi-blacklist.conf file has to be edited and the line 'blacklist spi-bcm2708' must be 'commented out'.  Once edited the line should read as (the hash makes the line a comment):

     #blacklist spi-bcm2708

The file raspi-blacklist.conf can be edited by typing into the terminal interface:

     sudo nano /etc/modprobe.d/raspi-blacklist.conf

If you use the alternative technique of typing into the terminal the instruction:

     sudo modprobe spi-bcm2708

then you will have to do this every time the R-Pi is restarted. Now restart the R-Pi.

B1.5 Installation and Configuration of the Apache2 Web Server

The new software written for this project makes use of a Web Server. To install the Apache2 Web Server, using the LXTerminal application type the following instructions:

     sudo apt-get install apache2

Now that the Web Server has been installed it has to be configured to support the running of Python programs. All of the web pages must be placed in the folder /var/www whereas the Python programs must be placed in the folder /usr/lib/cgi-bin. Whereas Apache is already configured to handle '.html' files it must be configured to execute the '.cgi' and '.py' files. Again using the LXTerminal application type the instructions:

     cd //

     cd /etc/apache2/sites-available

Now make a copy of the current default file so that the regional can be reused at a later date.

     sudo cp default old_default

Now edit the current 'default' file by starting the editor:

     sudo nano edit default

In the section starting ScriptAlias /cgi-bin /usr/lib/cgi-bin/ the flowing line must be added:

     AddHandler cg-script .cgi .py

Save the change and exit the editor. Now restart Apache:

     sudo restart apache2

This new line has configured Apache2 so that any script files in the folder /usr/lib/cgi-bin which have a file extension of '.cgi' or '.py' are scripts that can be called and executed from '.html' files.

B2 The Standard Gertboard Control Software

Testing of the configuration and wiring, and use of the Gertboard uses the software written by A.Eames of Raspi.TV. This software is written in Python 2.7. The software can be downloaded to your computer or via a browser by visiting the web-site: http://raspi.tv/downloads. To get the software directly on your Internet connected R-Pi then, working in LXTerminal, use the 'cd' instruction to change directory to that where you want the programs installed, now type the commands:

     wget http://raspi.tv/download/GB_Python.zip

     unzip GB_Python.zip

     cd GB_Python


These instructions will download and establish the directory GB_Python in which is stored the set of Gertboard Python test programs (each of the Python programs has a '.py' file extension). The 'README.txt' file provides further instructions on how to configure the operating system to enable the programs to be used with a Gertboard. The programs are supplied in two flavours: one using the RPi.GPIO Python module (RPi.GPIO is installed in all Raspbian operating system from Sept 2012 onwards) and one using the WiringPi for Python module (the instructions on how to install the WiringPi module are provided in Appendix B1.3). Both may be required depending on what you are going to do with the Gertboard using Python. For example, RPi.GPIO cannot be used to drive the Gertboard's pulse code modulation (PCM) capability. Three programs will be used to test and demonstrate the use of the Gertboard:

1. leds-rg.py - test of the buffered output ports and the inboards LEDs using the RPi.GPIO module
2. buttons-rg.py - test of the onboard buttons and the buffered input ports using the RPi.GPIO module
3. atod.py - test for ADC using the SPI on the Gertboard with the 'spidev' module (this also requires configuration of the SPI as described in Appendix B1.4).

B3 Web-based Gertboard Control Software

B3.1 Installing the Software

The software written for this project is available in the Element14 GitHub at: https://github.com/element14/pi_project/tree/master/Gertboard_Introduction. A clone of this software should be established using an appropriate software versioning application. The clone can be established at: https://github.com/element14/pi_project.git. The software is collected in two folders: 'cgi-bin' and 'www'. The software files are:

'cgi-bin' folder

• Buttontestv1p0p0.py - the python script to run the button test;
• Ledtestv1p0p0.py - the python script to run the led test;
• Pottestv1p0p0.py - the python script to run the potentiometer test.

'www' folder

• GertboardTestv1p0p0.html - the webpage you see on the remote browser;
• ButtonTestButton.png - the image for the “Button Test” button;
• LEDTestButton.png - the image for the “LED Test” button;
• PotTestButton.png - the image for the Potentiometer “Pot Test” button.

The files in the 'www' folder should be copied into the R-Pi directory '/var/www/' and the file in the 'cgi-bin' folder should be copied into the R-Pi directory '/usr/ib/cgi-bin/'. The next step is to make sure that these files have the correct access rights i.e. readable and exectable by Apache2. Using the LXTerminal application type the following instructions:

     cd //

     cd /var/www

     sudo chmod 755  GertBoardTestv1p0p0.html

     sudo chmod 755  ButtonTestButton.png

     sudo chmod  755 LEDTestButton.png

     sudo chmod  755 PotTestButton.png

     cd //

     cd /usr/lib/cgi-bin

     sudo chmod 755  Buttontestv1p0p0.py

     sudo chmod 755  Ledtestv1p0p0.py

     sudo chmod 755  Pottestv1p0p0.py

B3.2 Using the Software

To use and test that the software has been correctly installed start a browser on a device that is on the same local network as the R-Pi. In your browser type in the location (the URL for the test page):

     http://<Your IP Address>/GertBoardTestv1p0p0.html

The 'Your IP Address' can be obtained using the LXTerminal application and typing the command:

     Hostname -I

If the software has been installed correctly the web page show in Figure B3.1 should be displayed on your browser. If not, then read the Troubleshooting instructions.

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B3.3 Design of the Software

The design of this new software is largely based upon that by Alex Eames (RasPi.TV) and his use of the 'WiringPi.py' module, to demonstrate the use of the Gertboard. The aim has been to take this software and convert it to an equivalent form that can be accessed through a Browser and Web Server. The WiringPi and RPi.GPIO software both require root access hence using the command 'sudo' to run one of the test programs. There is no equivalent command in a Browser but the corresponding Python programs used by the Web Server make use of 'bash' shell commands to achieve the same access to the R-PI's GPIO interface.

The core HTML code for the web-page is shown below:

01     <html xmlns="http://www.w3.org/1999/xhtml">

02     <head>

03          <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

04          <title>Gertboard Test Program</title>

05     </head>

06     <body>

07          <h1>Gertboard Test Page</h1>

08          <p>Press one of the buttons below to start the corresponding test.</p>

09          <table>

10            <tr>

11              <td><div align="center"><a href="/cgi-bin/Ledtestv1p0p0.py"><img src="LEDTestButton.png" width="155" height="89" alt="LED Test Button"/></a></div></td>

12              <td><div align="center"><a href="/cgi-bin/Buttontestv1p0p0.py"><img src="ButtonTestButton.png" width="155" height="89" alt="Button Test Button"/></a></div></td>

13              <td><div align="center"><a href="/cgi-bin/Pottestv10p0.py"><img src="PotTestButton.png" width="155" height="89" alt="Potentiometer Test Button"/></a> </div></td>

14            </tr>

15            <tr>

16              <td><div align="center">Run LED Test Sequences</div></td>

17              <td><div align="center">Press up to 10 buttons in 10 seconds</div></td>

18              <td><div align="center">Potentiometer Test</div></td>

19            </tr>

20          </table>

21     </body>

22     </html>

The key features are lines 11-13 which define the code that is to be run on the Web Server when the associated 'button' on the web-page is pressed. For example, in line 11, the image 'LEDTestButton.png' is used to invoke the Python code in the file 'Ledtestv1p0p0.py' in the 'cgi-bin' directory. When a user presses the image, an HTTP call is sent to the Web Server which upon receipt runs the corresponding Python program. In this case it causes the LED test sequence to be completed. Once competed the Python code redraws the web-page on the browser in preparation for another user action.

Appendix C - The External Interface Board

C1 The Board Layout

The layout of the external interface board is shown in Figures C1.1a (top view), C1.1b (bottom view), C1.1c (side) and C1.1d (side). The external board is used to house the 12 external LEDs, the two external switches and the potentiometer.

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C2 The LEDs

Twelve LEDs are supplied on the board i.e. one for each of the output buffers available on the Gertboard. As shown in Figures C1.1a and C1.1b, each LED has two pins, the Anode (A) and the Cathode (C). These LEDs have a forward voltage of approximately 2.0V-2.2V with a forward current of 20mA. The output voltage across an I/O buffer on the Gertboard was measured at 2.3V and so no drop-down resistor is required.  As shown in Figure C1.1b, each LED is wired to 2-way square pin Molex Header with pins 'J' and 'K' with 'A' wired to 'J' and 'C' wired to 'K'. If a drop-down resistor is used then this would be inserted between pins 'J' and 'A'.

C3 The Switches

Two external push-button switches are supplied on the board. As shown in Figures C1.1a and C1.1b these each have two pins 'X' and 'Y'. Connection to each of the set of pins is achieved using a 2-way square pin Molex Header. It does not matter which way round these 'X' 'Y' pins are connected to the Gertboard.

C4 The Potentiometer

The Pot is used to demonstrate the operation of the ADC functionality of the Gertboard. As shown in Figures C1.1a and C1.1b, the Pot has three pins 'A', 'B' and 'C'. The central pin 'B' is the wiper and pins 'A' and 'C' should be connected to the high (3.3V) and ground (0V); it does not matter which way round pins 'A' and 'C' are connected unless the direction in which the potentiometer is to be rotated is important. A rotational pot is used herein but this could be replaced by any equivalent form of pot e.g. linear slider. Connection to the three pins is achieved using a 3-way square pin Molex Header.

Terminology

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