Wireless Smart Home

A wireless smart home designed using 900 MHz radios to allow for independent use, security, and easy setup.

David Pitt Erik Gustafson Lauren Giannotti

Each peripheral within the system must be implemented using some type of board used for prototyping electronics.

Author: David Pitt

November 7, 2017

Table of Contents Overview ……………………………………………………………………………………. 3 Risk Specifications ……………………………………………………………...………...….. 3 Risk Investigation ………………………………………………………………..…………... 4,5 Risk Mitigation Design ………………………………………………………………….…... 6-8 Parts List …………………………………………………………………………………….. 9 Testing Strategy ……………………………………………………………………………... 9 Uncertainties ……………………………………………………………………………….....9, 10 Appendices …………………………………………………………………………………... 10

I. Overview The objective of this project is to create a Smart Home system on an independent radio network that is not connected to wifi. The system will be capable of communicating with various peripherals such as light switches, a thermostat, etc. Each of these peripherals need to be connected to the system through some type of board. The board must be easy to various designs and be capable of relatively permanent implementations once the design is complete. The type of board that was chosen to be used for the majority of the peripheral implementation was a Perfboard.

II. Risk Specifications Customer Needs: 1. The system is capable of easily incorporating additional peripherals. 2. The master can communicate with numerous individual peripheral devices 3. The master has the ability to communicate with peripherals while it is disconnected from the Internet. 4. The system is affordable.

Marketing Engineering Requirements Justification Requirements

1, 2 A. The system can accept at least 50 People will not use a system that is peripheral devices. incapable of connecting multiple input and output devices.

4 B. The main unit should cost less than A successful product will need to be cheap $250, and each peripheral should enough for people to purchase. cost less than $75 each.

2, 3 C. The system’s peripherals should The system needs to respond to user respond to an input in less than 1 input in a timely manner in order to be a second whether it’s an input feasible, usable technology. peripheral or an input on the master. Table 1: Engineering Requirements ​

III. Risk Investigation Existing Systems: While there are many different types of boards that can be used for prototyping electronics, three different types of boards were investigated in the context of this project. Each board was analyzed in terms of its advantages and disadvantages and how those might apply to this project. The three different types of boards that were analyzed were a , a perfboard, and a (PCB). 1. A breadboard is simplest method of prototyping electronics. Implementing a circuit on a ​ breadboard does not require soldering, which allows for connections to be created and destroyed easily. This is useful for prototyping various circuits for which the design may not be finalized as it allows for experimentation in design. Some of the drawbacks of using are the inability to create large or complex systems due to the fact that breadboards are typically relatively small and cannot accommodate very high voltages or currents. Implementing a complex system using a breadboard is also difficult due to the large number of wires needed to create the system. A breadboard could be used to implement the peripherals required for this system. Due to the size of the system, however, it could become difficult to implement anything too complex. While the ability to implement a circuit without soldering is useful for prototyping, a more permanent implementation would be necessary for this project. 2. A perfboard is a thin sheet with a square grid of holes drilled into it. Components can either be ​ soldered onto the board or connected using other techniques such as wire wrapping. The connections made on a perfboard can be undone, which makes them useful for prototyping different designs of a system, but a perfboard implementation of a circuit is more permanent than that of a breadboard. The main drawback of a perfboard is the time needed to create each connection to implement the entire system, which can be tedious if the same system needs to be implemented multiple times or if there are a large number of systems being created. Implementing the peripherals required for this system could be done using a perfboard as it allows for the experimentation with various designs as well as permanence once the design has been finalized. However, if there are a large number of peripherals it could lead to an excessive amount of time required to construct each system on the perfboard. 3. A printed circuit board, or PCB, uses conductive tracks that are etched onto copper sheets ​ laminated onto a non-conductive substrate to create electric connections. Components that are implemented on a PCB are soldered onto the board. PCBs are very difficult to modify once implemented, which means they are not useful for prototyping or experimenting with different designs. The main advantage of PCBs are the ability to create multiple identical circuits. If the design of the circuit is already finalized, using PCBs make it easy to create as many copies of the design as necessary. If the design of the implementation for a specific peripheral has already been tested and verified, using PCBs would be very beneficial for creating multiple copies of the design. If the design has not been finalized, however, using a PCB to implement the circuit would not be useful because of its inability to be modified after it has been created. Concepts Considered: Based on the information gathered from each of the existing systems it was determined that one of the features that will be needed for the board used is the ability to experiment and modify the designed circuit due to the fact that the system design has not been finalized. It is also important that the board used allows for the finalized circuit design to be implemented in a somewhat permanent manner. The ability to produce multiple identical circuits once the design has been finalized was determined to be a potential factor for certain peripherals, but is not the primary functionality that is needed for the implementation of this system. Each of the three types of boards that were investigated were analyzed with these criteria in mind, and a point value between one and ten was assigned to each board type for each criteria. The results of this analysis is shown in Table 2.

Board Type Difficulty to Room for Permanence Reproducibility Assemble Modification

Breadboard 2 10 3 5

Perfboard 6 6 8 3

PCB 5 2 10 10 Table 2: Board Type Proficiency for Each Primary Criteria ​ Analysis: ​ Based on the specified significance of each criteria and the assigned values for those criteria for each board type it was determined that a perfboard would be the most useful for the majority of designs in this project. Due to the fact that the design of each system is not finalized, it is important that perfboards are capable of being modified so that the designs can be experimented with until a definitive design is achieved. In order to integrate these circuits into the entire system, the designs must be somewhat permanent. It is worth noting, however, that there could be certain circuit designs end up requiring multiple copies of the same design. In these cases, it might be beneficial to use a perfboard to determine the final design, and then use a PCB to implement the finalized design to create multiple copies of the same circuit.

IV. Risk Mitigation Design

Overview: There are three main types of circuits that will need to be implemented for this project. The results of these circuits will either be a device that can read a particular value, change a value, or a more complicated device that involves the integration of some sort of microcontroller. An input device that simply reads a value consists of some sort of input connection that connects to the power supply and to the radio module. A switch connected to a pull-up circuit will act as the input and connect to the GPIO pin of the radio module, which will be read as an input. An output device will also consist of an input connection that connects to the power supply and the radio module, but the GPIO output of the radio module is instead connected to a switch that is connected to the output plug. In addition to basic input/output device circuits, a more complicated circuit will be necessary to implement any peripheral that involves the use of a microcontroller or any other small device. How this mitigates risk: In order to implement the basic input/output device circuits a perfboard will be used. All of the components involved in these circuits are fairly large and are thus easy to lay out individually on a board. Due to the fact that it is fairly easy to implement a circuit on a perfboard, they are ideal for implementing basic devices such as switches. These circuits will be easy to implement and test and should not require extensive modifications after being designed. In the case of a more complicated device that uses a microcontroller, such as a temperature sensor, A PCB will most likely be ideal. This is because more complex designs have smaller parts and need to be more precise, which if implemented by hand on a perfboard would have a high chance of failing. By designing complex systems on a PCB, there is a much higher chance of the device behaving as intended. In this case, even though a perfboard may be advantageous due to the ease of implementation, it is worth it to use a PCB instead in order to minimize the risk of the device failing. Design: An input device will be used to read in some sort of input such as the pressing of a button. The input connection leads to the power supply which feeds into the radio module. A switch connected to a pull-up resistor acts as the input of the circuit and feeds into the GPIO pin of the radio module to convey whether the switch is opened or closed. An overview of this design is shown in Figure 1.

Figure 1: Basic input device schematic ​ An output device circuit also consists of an input connection feeding into the power supply and subsequently into the radio module. In this case, however, the GPIO pin of the radio module is used as an output which is fed into a relay that determines whether the output is high or low based on the original input signal. This schematic is shown in Figure 2.

Figure 2: Basic output device schematic ​ Both the input and output devices will implemented as circuits on a perfboard. Due to the large size of each individual components, the circuit is easy to implement and there is little risk in the device failing or behaving in an unexpected manner. Any device that involves the use of a microcontroller such as a temperature sensor, however, would be better to implement using a PCB. Just as in the input and output device schematics, an input connection feeds into the power supply and then to the radio modules. In the more complex circuits the radio module outputs two UART signals that feed into the microcontroller which can interpret the data accordingly. An overview of what this schematic would look like is shown in Figure 3.

Figure 3: Schematic of complex circuit involving a microcontroller ​ Intellectual Property: Due to the fact that the circuits discussed thus far are not inherently novel, there is no patent to consider for these devices. Some areas for future consideration in terms of intellectual property could involve patents on certain types of devices like temperature sensors. For the sake of this investigation, however, there are no patents that need to be taken into consideration.

V. Parts List The list of parts required for this design are shown in Table 3.

Part Description Cost Your Cost Availability Perfboard 20 20 Immediate online purchase PCB 35 35 Takes approx. 4 week after order Radio Module 30 30 Immediate online purchase

VI. Testing Strategy

Due to the simplicity of the majority of the circuits involved in this project, each individual circuit will not require extensive testing. An input device can be tested by connecting the switch to some sort of button and verifying the fact that the system is registering the pushing of the button by setting the switch to a particular state. Testing an output device will involve using various input signals and ensuring that the output responds properly to the specific input. The more complicated circuits will require slightly more testing in order to ensure that the devices are working properly, such as making sure that a temperature sensor device is properly responding to changes in temperature and recording accurate results.

VII. Uncertainties Due to the fact that there is not a known definitive number of peripherals that will be implemented or a known number of copies for each circuit, it is difficult to determine how extensive the experimenting portion of the design will be. The design of a particular circuit could be very simple or complex, which makes it difficult to determine whether a PCB or a perfboard should be used. In reality, a mixture of these two could end up being the ideal option. In addition to this, depending on the peripheral multiple copies of the same circuit may or may not be needed. Until the entire system has been designed to specify the total number of peripherals and the number of copies of each circuits that will be required it is difficult to determine the correct type of board that will be necessary. Based on the analysis performed on each of the board types, it appears that the majority of designs will be done using perfboards, but certain designs might end up lending themselves more towards using PCBs.

Appendices http://www.dartmouth.edu/~sullivan/prototyping.pdf https://forum.allaboutcircuits.com/threads/choosing-pcb-versus-perfboard.44877/ https://www.jameco.com/jameco/workshop/techtip/wirewrap.html http://quinndunki.com/blondihacks/?p=835 http://geofex.com/Article_Folders/protostyles/proto_styles.htm