An Introduction to Using the Embedded-Pi 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 R-Pi, E-Pi and Sensor Shield
   • Demonstrating the Sensor Shield LED Actuator Module
   • Demonstrating the Sensor Shield Button Sensor Module
   • Demonstrating the Sensor Shield Tilt Sensor Module
   • Demonstrating the Sensor Shield Relay Actuator Module
6. Using the Embedded-Pi
   • Configuring the Hardware
   • Demonstrating Embedded Pi with Sensor Shield LEDs
   • Demonstrating Embedded Pi with Sensor Shield Buttons
   • Demonstrating Embedded Pi with Sensor Shield Tilt Sensor
   • Demonstrating Embedded Pi with Sensor Shield Relay Actuator
7. Trouble Shooting
8. Appendix A - The Embedded Pi
9. Appendix B - The Software
   • System Software
   • The Embedded Pi/Sensor Shield Python Demonstration Software
10. Appendix C - The Arduino TinkerKit Sensor Shield
11. Terminology
12. About this Document

Overview

This Project is about introducing the use of the Embedded Pi (E-Pi) to extend the functionality of the Raspberry Pi (R-Pi). The Embedded Pi provides an R-Pi with an interface to Arduino Shields without the use of an Arduino device. In this set of instructions the R-Pi/E-Pi combination is used to drive a TinkerKit Sensor Shield with a set of sensors/actuators:

• LED actuator - to switch an LED on and off;
• Button sensor - to sense the state of a button/switch;
• Tilt sensor - to sense when an object is being tilted;
• Relay actuator - to use a low power device to control the on/off state of a high power device.

The key learning objectives of this project are for an intermediate/novice developer to learn:

• How to use a combination of the R-Pi, E-Pi and Sensor Shield to control a set of sensors and actuators;
• How to write Python software that is used to control/detect the state of the sensors/actuators.

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 Embedded Pi available on the Element14 Community Embedded Pi 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. Network connectivity is required to install the necessary software updates and the Embedded Pi demonstration 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 and, if required, the WiPi. 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;
• Embedded Pi (E-Pi) - the E-Pi provides an interface platform to the R-Pi, Arduino and the 32-bit embedded ARM processor. For this set of instructions the E-Pi is used as a bridge between the R-Pi and Arduino Shields. This interface is physically achieved using the GPIO connectors on the R-Pi and E-Pi. The software interface is achieved using the RPi.GPIO and WiringPi modules. The Embedded Pi User Manual (Revision 1.0 published in May 2013 by CooCox) is available at: Embedded Pi User Manual. This is required reading. Details on the CooCox development environment, this is not used in this project, are available Here;
• TinkerKit Sensor Shield - this allows TinkerKit sensors and actuators to be connected directly to an Arduino or E-Pi without the use of a breadboard. The Sensor Shield has 12 standard TinkerKit 3-pin connectors. The 6 labelled 'I0' to 'I5' are the Analog Inputs and the 6 labelled 'O0' to 'O5' are the Analog Outputs (these can be driven using PWM capable outputs or can be configured as digital inputs).  In this set of instructions only the 'O0' to 'O5' pins are used. Further information is available at TinkerKit Sensor Shield;
• Sensor Shield Sensors and Actuators - in this set of instructions the LED and Relay actuators and the Button and Tilt sensors modules fromTinkerKit are used (they are plugged into the 'O0' to 'O5' pins on the Sensor Shield). The use of sensor and actuators being used together is also demonstrated.

Figure 1.1 System Configuration.

When the complete system is built it will have various forms as shown in Figure 1.2.  The views shown in Figure 1.2 are for LED modules (a), Button modules (b), Tilt module (c) and Relay module(d).

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2. Bill of Materials

2.1 System Configuration

The architecture is based upon the use of an R-Pi, an E-Pi, a TinkerKit Sensor Shield and a set of sensors and actuators. The configuration is shown in Figure 2.1 and the key to the alphanumeric labels is provided in Tables 2.1 and 2.2.

Figure 2.1 System configuration for the bill of materials

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 - The 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).

3. Set of Instructions

The set of instructions for using the E-Pi are:

1. Configure the R-Pi system in preparation for the connection of the E-Pi and usage of the demonstration 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 together the R-Pi, E-Pi and the Sensor Shield. A demonstration of this is shown in Video 1. The R-Pi and E-Pi are connected via the GPIO interfaces using the flat-flex cable (supplied as part of the E-Pi kit). It is important to ensure that the two GPIO interfaces are connected correctly and so use the red edge on the flat-flex cable to confirm the correct alignment of the interfaces. The Sensor Shield is placed on top of the E-Pi and connected using the set of pins on the underside of the Sensor Shield and the outer set of sockets on the E-Pi Arduino Form-Factor Compatible interfaces. Set the E-Pi power bus voltage to 3.3V (using Jumper JP1). Finally the E-Pi must be configured for the R-Pi mode by making sure that only the Jumper JP3 ('R') is present of the JP3 ('R') and and JP4 ('S') pair - see More Detail;
3. To use the LED modules take the 3-pin twisted wires cable that were supplied with the TinkerKit Sensor Shield Base Kit and connect the LED modules to the orange sockets (Analog output) on the Sensor Shield. Download the Python software program 'epi-leds-rgv1p0p0.py' from the Element14 GitHub repository and run it using the LXApplication. A demonstration of this software is shown in Video 2 - see More Detail;
4. To use the Button modules take the 3-pin twisted wires cable that were supplied with the TinkerKit Sensor Shield Base Kit and connect the Button modules to the orange sockets (Analog output) on the Sensor Shield. Download the Python software program 'epi-buttons-rgv1p0p0.py' from the Element14 GitHub repository and run it using the LXApplication. A demonstration of this software is shown in Video 3 - see More Detail;
5. To demonstrate the use of the Tilt Switch module connect it and one of the LED modules to the orange sockets (Analog Output) on Sensor Shield using the 3-pin twisted wires cables. Note that the Tilt Switch should be connected to the orange socket 'O0' and the LED to orange socket 'O1'. Download the Python software program 'epi-tilt-rgv1p0p0.py' from the Element14 GitHub repository and run it using the LXApplication. While the software is running vary the orientation of the Tilt Switch and observe the brightness of the LED (it should be possible to turn the LED 'on' and 'off' by varying the orientation of the Tilt Switch). A demonstration of this software is shown in Video 4 - see More Detail;
6. To demonstrate the use of the Relay module connect it and a Button module to the Sensor Shield (via the orange sockets 'O3' and 'O2' respectively) using two 3-pin twisted wires cables. The Relay is used to control current flow through a separate circuit and for this demonstration a small red LED is wired to the Relay such that the LED is 'off' under normal operation. The power to the red LED is drawn from convenient 3.3V and ground pins on the E-Pi via the Power Socket on the Arduino Form-Factor Compatible Interface on the Sensor Shield. The demonstration involves the Button being pressed to close the Relay and thus light the red LED. When the Button is pressed again, the Relay is opened and the LED turned 'off'. Download the Python software program 'epi-relay-rgv1p0p0.py' from the Element14 GitHub repository and run it using the LXApplication. A demonstration of this software is shown in Video 5 - 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.

Figure 4.1 - R-Pi Model B board layout.	Figure 4.2 - The R-Pi with the set of connected cables.
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4.2 Connecting the R-Pi, E-Pi and Sensor Shield

Once the R-Pi has been configured, the next step is to connect the E-Pi and Sensor Shield in preparation for using the various sensor and actuator modules. The E-Pi is connected to the R-Pi using the GPIO flat-flex cable as shown in Figure 4.3 (note the positioning of the red edge of the flat-flex cable with respect to the orientation of the R-Pi and E-Pi).

Figure 4.3 - R-Pi and E-Pi connection.

The Sensor Shield is inserted into the outer set of pins on the E-Pi i.e. the Arduino Form-Factor Compatible Interface (see Appendix A): this connection is shown in Figure 4.4 (Figure 4.4d showing the use of the outer set of pins). The GPIO pins on the underside of the E-Pi are used to connect to the R-Pi as shown in Figure 4.4a.

When all three devices are connected, the layout is as shown in Figure 4.5. Note that in Figure 4.5 the JP3 ('S') jumper has been removed to prepare the E-Pi to operate in R-Pi mode (see Appendix A for more details on the JP3).

Figure 4.5 - The connected R-Pi, E-Pi and Sensor Shield.

See Video 1 for a demonstration of how to connect the R-Pi, E-Pi and Sensor Shield.

4.3 Demonstrating the Sensor Shield LED Actuator Module

The LED modules are connected to the Analog Output (orange) sockets on the Sensor Shield using the 3-pin wires. The green LED on the module board will be lit when the E-Pi/Sensor Shield is powered. The Sensor Shield can support up to six LED modules all of which are controlled independent of each other. See Figure 4.6 for the connection of the demonstrator. The order of the LEDs connected to the Sensor Shield is not important because the software drives all of the output sockets.

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Once the hardware has been configured the demonstration software should be used. Download the Python software program 'epi-leds-rgv1p0p0.py' from the Element14 GitHub repository - see Appendix B. To run the software use the LXApplication and type the following instruction:

     sudo python epi-leds-rgv1p0p0.py

Now follow the instructions printed on the terminal. This program will now switch the LEDS on and off in a number of predefined sequences. A commentary on the activity of the program is printed on the terminal display. This program can be changed to reflect any personal preferences on the control of the LEDs. See Video 2 for a demonstration of the operation of this software.

4.4 Demonstrating the Sensor Shield Button Sensor Module

The Button modules are connected to the Analog Output (orange) sockets on the Sensor Shield using the 3-pin wires. The green LED on the module board will be lit when the E-Pi/Sensor Shield is powered. The Sensor Shield can support up to six Button modules all of which are controlled independent of each other. See Figure 4.7 for the connection of the demonstrator. The actual orange sockets used to connect to the Sensor Shield is not important because the software monitors all of the output sockets.

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Once the hardware has been configured the demonstration software should be used. Download the Python software program 'epi-buttons-rgv1p0p0.py' from the Element14 GitHub repository - see Appendix B. To run the software use the LXApplication and type the following instruction:

     sudo python epi-buttons-rgv1p0p0.py

Now follow the instructions printed on the terminal. This program will now monitor the state of the buttons and display this state on the terminal window. A commentary on the activity of the program is printed on the terminal display. This program can be changed to reflect any personal preferences on the control of the buttons. See Video 3 for a demonstration of the operation of this software.

4.5 Demonstrating the Sensor Shield Tilt Sensor Module

In this demonstration the Tilt Switch is used to drive the state of an LED i.e. when the Tilt switch is upright the LED is 'on' otherwise the LED is 'off'. The Tilt Switch and LED modules are connected to the Analog Output (orange) sockets on the Sensor Shield using the 3-pin wires. The green LED on the module board will be lit when the E-Pi/Sensor Shield is powered. See Figure 4.8 for the connection of the demonstrator. It is important to connect the LED and Tilt Switch to the correct orange sockets otherwise the software will not work correctly (unless it is also modified to reflect the different sockets connections). The software assumes that the Tilt Switch is connected using socket 'O1' and the LED using socket 'O0'.

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Once the hardware has been configured the demonstration software should be used. Download the Python software program 'epi-tilt-rgv1p0p0.py' from the Element14 GitHub repository - see Appendix B. To run the software use the LXApplication and type the following instruction:

     sudo python epi-tilt-rgv1p0p0.py

Now follow the instructions printed on the terminal. While the demonstration software is running vary the orientation of the Tilt Switch and watch the corresponding change in state of the LED module and the logging on the terminal. A commentary on the activity of the program is printed on the terminal display. This program can be changed to reflect any personal preferences on the use of the Tilt Switch. See Video 4 for a demonstration of the operation of this software.

4.6 Demonstrating the Sensor Shield Relay Actuator Module

In this demonstration the state of the Relay module is controlled using a Button module. The Relay and Button modules are connected to the Analog Output (orange) sockets on the Sensor Shield using the 3-pin wires. See Figure 4.9 for the connection of the demonstrator. It is important to connect the Relay and Button modules to the correct orange sockets otherwise the software will not work correctly (unless it is also modified to reflect the different sockets connections). The software assumes that the Relay is connected using socket 'O3' and the Button using socket 'O2'. The small red LED, see Figure 4.9a, is connected to the power pins on the E-Pi Power port .e. one of the GND pins and the 3.3V pin. The aim is to show that when the Relay is closed the current can flow through the red LED and thus show that the relay has changed state. The drop-down resistor (approx 180 Ohm) is used to ensure that the voltage drop across the LED is not more than 2.2V (the connection to the E-Pi is configured to supply a voltage of 3.3V). The red LED is wired to the 'NO' port on the Relay and so the circuit is normally open.

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Once the hardware has been configured the demonstration software should be used. Download the Python software program 'epi-relay-rgv1p0p0.py' from the Element14 GitHub repository - see Appendix B. To run the software use the LXApplication and type the following instruction:

     sudo python epi-relay-rgv1p0p0.py

Now follow the instructions printed on the terminal. The state of the Relay is changed by pressing the Button.  At the start, the Relay is open (the small red LED is also off) and when the Button is pressed the Relay is closed (the red LED is now turned on). If the Button is pressed again then the Relay opened (the red LED is now off). Note that there is an audible click every time the state of the Relay is changed. A commentary on the activity of the program is printed on the terminal display. This program can be changed to reflect any personal preferences on the use of the Relay module. See Video 5 for a demonstration of the operation of this software.

5. Using the Embedded-Pi

All of the videos below are available in medium resolution (a) and high resolution (b) - the high resolution will require at least a 3.5Mbps broadband data rate to view in streamed mode.

5.1 Configuring the Hardware

A video, 8 minutes long, demonstrating the wiring together of the R-Pi, E-Pi and Sensor Shield is shown in Video 1.

Video 1 - Wiring the R-Pi, E-Pi and Sensor Shield.
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5.2 Demonstrating the Embedded Pi with Sensor Shield LED

A video, 4 minutes long, demonstrating the use of the R-Pi, E-Pi and Sensor Shield to control LEDs is shown in Video 2.

Video 2 - Demonstrating the R-Pi, E-Pi and Sensor Shield to drive a set of LEDs.
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5.3 Demonstrating Embedded Pi with Sensor Shield Buttons

A video, 4 minutes long, demonstrating the use of the R-Pi, E-Pi and Sensor Shield to sense the state of Buttons is shown in Video 3.

Video 3 - Demonstrating the R-Pi, E-Pi and Sensor Shield to sense the state of buttons.
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5.4 Demonstrating Embedded Pi with Sensor Shield Tilt Sensor

A video, 2 minutes long, demonstrating the use of the R-Pi, E-Pi and Sensor Shield to sense the state of a Tilt Switch and to use an LED to show that state is shown in Video 4.

Video 4 - Demonstrating the R-Pi, E-Pi and Sensor Shield to sense the state of a Tilt Sensor.
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5.5 Demonstrating Embedded Pi with Sensor Shield Relay Actuator

A video, 3 minutes long, demonstrating the use of the R-Pi, E-Pi and Sensor Shield to change the state of a Relay actuator using a Button/switch is shown in Video 5.

Video 1 - Demonstrating the R-Pi, E-Pi and Sensor Shield to control the state of a Relay actuator.
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6. Trouble Shooting

Appendix A - The Embedded Pi

The layout of the E-Pi is shown in Figures A1.1 and A1.2. The E-Pi is supplied with the GPIO flat-flex cable (see Figure A1.3) and the plastic stands (see Figure A1.1c): the latter should be inserted into the E-Pi so that the underside is not damaged when the E-Pi is being used. The TinkerKit Sensor Shield is connected using the two outer sockets labelled as the Arduino Form-Factor Compatible Interface. The GPIO interface is one of the male set of pins on the underside (see Figure A1.1b). The other set of pins on the underside are the debug interface that enables the internal operation of the E-Pi to be observed using a set of test software (see the CooCox Embedded Pi User Manual for more details - this interface is not used in this set of instructions). The GPIO ports are directly mapped to the Analogue Output/Digital Input pins that are part of the Arduino Form-Factor Compatible Interface. The details of the various GPIO pin numbers and relationships between the Arduino Form-Factor and the R-PI are defined in Table 3.7 in the Embedded Pi User Manual.

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The use of the three jumpers JP1, JP2 and JP3 is summarised in Table A1.1.

Table A1.1 - Use of the Jumpers of the E-Pi.

The various side images of the E-Pi are shown in Figure A1.2. In these image both the 'R' and 'S' jumpers are present and the voltage is set to 3.3V. To set the E-Pi for R-Pi mode the 'S' jumper must be removed.

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The R-Pi and E-Pi are connected using the GPIO interface and the flat-flex cable supplied with the E-Pi. The GPIO cable is connected as shown in Figure A1.3 i.e. the red edge is at the top such that the dimple on the actual connector (dimple cannot be seen in Figure A1.3) faces into the rest of the R-Pi.

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Appendix B - The Software

B1 System Software

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.

B2 The Embedded Pi/Sensor Shield Python Demonstration Software

The demonstration Python software written for this project is available in the Element14 GitHub at: https://github.com/element14/pi_project/tree/master/EmbeddedPi_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 files are:

• epi-leds-rgv1p0p0.py - to demonstrate the use of the TinkerKit LED actuator. This drives six LEDs connected to the 'O0' to 'O5' sockets on the Sensor Shield;
• epi-buttons-rgv1p0p0.py - to demonstrate the use of the TinkerKit Button sensor. This monitors the state of any Buttons connected to the 'O0' to 'O5' sockets on the Sensor Shield;
• epi-tilt-rgv1p0p0.py - to demonstrate the use of the TinkerKit Tilt sensor with the TinkerKit LED actuator. This uses the 'O0' and 'O1' sockets on the Sensor Shield for the connection of the Tilt Switch and LED modules;
• epi-relay-rgv1p0p0.py - to demonstrate the use of the TinkerKit Relay actuator with the TinkerKit Button sensor. This uses the 'O2' to 'O3' sockets on the Sensor Shield for the connection of the Button and Relay modules.
  

The software requires that the RPi.GPIO Python module is installed (RPi.GPIO is installed in all Raspbian operating system from Sept 2012 onwards). The demonstration software is written in Python 2.7. The use of the RPi.GPIO module means that root access is required to run the software and so when using the LXTerminal, type the following to run one of the programs:

     sudo python <<program name>>

As each program runs it uses the display to provide the corresponding activity report, prompt for user input and to display the associated sensor/actuator input/output.

NOTE: This demonstration software does not need software downloaded and running on the Embedded Pi host processor itself. The E-Pi is used as a hardware connection conduit to the Sensor Shield with the E-Pi operating in R-Pi mode.

Appendix C - The Arduino Tinker Kit Sensor Shield

The layout of the TinkerKit Sensor Shield is shown in Figure C1.1. Figure C1.1a shows the top view and C1.1b the underside view. A Sensor Shield is just one of many Arduino Shields that are available. The Sensor Shield has two types of connector:

• Arduino form factor compatible interface pins - these pins are use to connect the Sensor Shield to the Arduino/E-Pi and to allow other Arduino Shields to be stacked. In this set of instructions the Sensor Shield will be plugged directly into the E-Pi using the pins on the underside of the Sensor Shield. Only one Sensor Shield is to be used.  It should be noted that if more than one Arduino Shield is used in a stack, there is no way to differentiate between those boards using the Arduino form factor compatible interface pins;
• Device/module sockets - the sockets used by the array of sensors and actuators that are available. There are four sets of sockets available:-
  • Analog Output/Digital Input Sockets - the set of 3-pin sockets that are used to provide analog output/digital input to the E-Pi/R-Pi. These sockets are labelled 'O0' to 'O5'. This set of instructions makes extensive use of these sockets because they can be directly controlled using the GPIO interface on the R-Pi/E-Pi. When using the GPIO interface, these six sockets can be used to provide a variety of digital inputs and digital outputs and so the appropriate sensor/actuator modules can be controlled. In Analog Output mode the socket behaves as a Pulse Width Modulation (PMW) interface
  • Analog Input Sockets - the set of 3-pin sockets that are used to provide analogue input to the E-Pi/R-Pi. These sockets are labelled 'I0' to 'I5'. This set of instructions does not make use of these sockets
  • Serial Socket - this 4-pin socket provides a serial interface. This interface is only available under some configurations. This set of instructions does not make use of this socket
  • TWI Socket - this 4-pin socket allows communication with any device supporting the I2C protocol. This set of instructions does not make use of this socket.

When the Sensor Shield is correctly connected and powered, through the E-Pi, then the 'Power LED' will be lit.

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The connections between the R-Pi/E-Pi/Sensor Shield are via a set of GPIO/Arduino Form Factor pins. There are a number of ways in which these pins are labelled and used and these relationships are summarised in Table C1.1. From an end-to-end respective the key label relationship is that between the held Output Port number (column one) and the R-Pi GPIO pin (column four). This provides the relationship between the device connected to the Sensor Shield (using the Output Port number) and the GPIO pin used within the corresponding Python software hosted on the R-Pi. In Table C1.1 the two middle columns show the relationship to the standard Arduino pin numbering and the E-Pi pin numbering.

Table C1.1 - Sensor Shield Output Ports to E-Pi to R-Pi to Arduino Pin number mappings.

The four sensor and actuator modules that are used in this set of instructions are shown in Figure C1.2. Each of these modules is connected to the Sensor Shield using the 3-wire connectors (see Figure 1.2).

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The capabilities of the modules shown in Figure C1.2 are:

• LED actuator - the brightness can be controlled by outputting a value of '0' to '-1023' to the LED. In digital mode the LED is on (1023) or off (0);
• Button sensor - detects when the circular cap is pressed. The module outputs a 5V when the button is pressed and 0V when released. When using the Sensor Shield a value of '1023' is detected when the button is pressed and '0' when released;
• Tilt sensor - when upright the sensor sends an analogue value of '0' and when tilted a value of '1023'. When using the Sensor Shield as a digital input on the 'O0' to 'O5' ports with the GPIO interface, the corresponding digital values are '0' and '1';
• Relay actuator - a device that is used to enable a low power device to electrically switch/control the state of a high power device. The module provides three connections labeled COM, NC and NO. NC stands for "NORMALLY CLOSED". This means that when the relay has no signal (LOW or 0V), the connected circuit wil be active; conversely, if you apply 5V or pull the pin HIGH, it will turn the connected circuit off. NO stands for "NORMALLY OPEN", and functions in the opposite way; when you apply 5V the circuit turns on, and at 0V the circuit turns off.

Terminology

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