ECE477: Team 10 Design Constraint Analysis and Component Selection Rationale

Transcription

1 TABLE OF CONTENTS 1 INTRODUCTION MASTER DEVICE SLAVE (SITE) DEVICE ANALYSIS OF DESIGN CONSTRAINTS COMPUTATIONAL REQUIREMENTS Master Device Slave (Site) Device INTERFACE REQUIREMENTS Master Device Internet Interface Bus Interface Slave (Site) Device Bus Interface Keypad Interface Occupancy Sensor Interface Switched Outlet Interface Audible Alarm Visible Timer POWER SUPPLY CONSTRAINTS PACKAGING CONSTRAINTS COST CONSTRAINTS RATIONALE FOR COMPONENT SELECTION MASTER DEVICE MICROCONTROLLER DS80C RCM RCM3700 (chosen) SLAVE (SITE) DEVICE MICROCONTROLLER PIC16C63A ATmega16L (chosen) KEYPAD CS KP-22 (chosen) RS485 TRANSCEIVER ISL MAX485 (chosen) LIST OF COMPONENTS LIST OF REFERENCES... 8 Page 1 of 8

2 1 Introduction The project will be an autonomous system for physical space management. The system will be designed to solve the real world problem of reserving office/lab space and enforcing a policy. There will be three main types of components: a master device, slave (site) device, and a connecting bus (self-explanatory). 1.1 Master Device The master device will run the Internet application, database, and site management software. The Internet application will allow administrators to make configuration changes. It will also allow users to schedule reservations and receive notifications. The database will be custom-designed for the specific needs of the project. The site management software will communicate across the bus to manage the site components. 1.2 Slave (Site) Device The slave (site) device will have a set of inputs and outputs available to the users in each site. Among the inputs, there will be a keypad for confirmation code entry (authentication) and an occupancy sensor to detect a prematurely abandoned site. Among the outputs, there will be a seven-segment display showing how many minutes remain in the reservation, an audible alarm to signal the 5-minute warning before the end of a reservation, and a switched electrical outlet. 2 Analysis of Design Constraints 2.1 Computational Requirements Master Device The master device will require a sophisticated microcontroller for several reasons. The Internet application must serve the web pages to a reasonable number of users in real time. The database will require that the microcontroller has as large as possible of a memory system. Finally, the site management software must have the ability to keep up with the needs of each site. For these purposes, the microcontroller chosen must be fast as well as have a large memory capacity. Page 2 of 8

3 2.1.2 Slave (Site) Device The slave (site) device will only require a simple microcontroller. Its main job will be to relay inputs back to the master and to drive outputs as instructed by the master. Very little memory will be required except to buffer the site state variables. The microcontroller only needs to be fast enough to keep up with the incoming instruction on the bus. 2.2 Interface Requirements Master Device Internet Interface The Internet connection should be reasonably fast, because it will need to be able to transmit web pages to many simultaneous users Bus Interface The bus interface does not need to be particularly fast, because data will typically only flow as conditions change. However, each device on the bus needs to be addressable Slave (Site) Device Bus Interface The same bus interface requirements apply from Section Keypad Interface The keypad will need to be capable of receiving a user s confirmation code which can be comprised solely of the digits 0-9. The keypad should also have a key that is used to send the code. A method of debouncing and encoding the keypad will be needed between the keypad and the microcontroller Occupancy Sensor Interface The occupancy sensor will need to be able to tell when the site has users. It must be able to see the entire site and not into other areas. This information will be used by the microcontroller to determine if the occupants have left the site before the end of a reservation so it can turn off equipment and allow other users. Page 3 of 8

4 Switched Outlet Interface The switched outlet will need to provide the same voltage and current as a standard electrical outlet only while the reservation is being used. The microcontroller must be able to activate the outlet Audible Alarm The audible alarm will need to be loud enough to alert unsuspecting users when the reservation is nearly over without being so loud that it is too annoying. The alarm will be activated by the microcontroller Visible Timer The visible timer should show the users how many minutes remain for the reservation. It should be large enough to read and contain at least 3 digits (to show a reasonable maximum of minutes). The microcontroller should control the display. 2.3 Power Supply Constraints Both devices will be located in office-type locations. For convenience, both devices should run off standard 115 VAC. Due to the nature of the system, power consumption (excluding that through the switched outlet) should remain low. 2.4 Packaging Constraints Both devices should be packaged in some type of case that is about shoebox sized and weigh only a few pounds. Each device should be capable of being hung on a wall for convenience. The slave (site) devices should be secured by means of a lock. 2.5 Cost Constraints The only cost constraint is to minimize cost without sacrificing functionality. 3 Rationale for Component Selection The following components were chosen based on availability and price and not considered major: 7-Segment LED Digital Display 85dB Piezo Buzzer 16-key encoder (74C922) SPDT relay Page 4 of 8

5 3.1 Master Device Microcontroller The only component to determine in the master device is the microcontroller. It needed to be fast, have a large memory, have at least a programmable timer, and provide possible interfaces to the internet and bus. Besides that, the development tools should be welltested, liked, dependable, and accessible DS80C400 The Dallas Semiconductor DS80C400 was identified because it an Ethernet connection. (In order to get around Ethernet, the next best solution would have been to connect to the Internet through another PC which eliminates the autonomy of the system.) This architecture can clock as fast as 75MHz. Unfortunately, there is only 1K of on-chip memory. The chip has four timers. In order to connect to an RS485 transceiver, there are extra ports. This family of chips has not been mentioned in class and quality of development tools is unknown. At 11, this microcontroller meets much of the criteria well, but falls short in two important ways: on-chip memory and unused tools RCM2250 The RabbitCore Module 2250 runs as fast as 22.1 MHz. It carries 1 MB of on-chip memory with 512KB of Flash and 512KB of SRAM. The chip has 6 timers. The 10Base-T RJ45 Ethernet connection is a standard component. The module should be able to interface to RS485 using a port. Finally, the Rabbit development software has good review from former teams. At 79, this microcontroller makes an excellent candidate RCM3700 (chosen) The RabbitCore Module 3700 runs as fast as 22.1 MHz. It carries 1 MB of on-chip memory with 512KB of Flash and 512KB of SRAM. According to the documentation, there are two timers that can be programmed to provide interrupts. The 10Base-T RJ45 Ethernet connection is a standard component. The module should be able to interface to Page 5 of 8

6 RS485 using a port. Finally, the Rabbit development software has good reviews from former teams. At 59, this microcontroller makes an excellent candidate. Since it was cheaper than the RCM2250, this is the choice for our master device microcontroller. 3.2 Slave (Site) Device Microcontroller The primary concerns for the choice of a slave device microcontroller were pins, ports, price, and development tools. Assuming that all simple outputs could be driven with 3 pins by using a shift register, the keypad input should require about 5 pins, the occupancy sensor should require just 1 pin for a total of 9 pins. The bus will just use a port PIC16C63A The PIC16C63A chip includes 22 I/O pins. It also includes SPI and USART. The price is under 4. Lecture notes mention that the PIC development tools are less than dependable. This microcontroller makes a good candidate ATmega16L (chosen) The Atmel ATmega16L chip includes 32 programmable I/0 lines, definitely enough to even skip the shift register. It also includes SPI and USART. The price is under 6. Finally, the Atmel processors are recommended based on a fine history of development for former teams. This microcontroller makes an excellent candidate. Since it was still cheap, had more than enough resources, and a reputation for dependable development tools, this is the choice for our slave device microcontroller. 3.3 Keypad The choice for the keypad primarily depended on the interface both internally to the microcontroller and to the user. Page 6 of 8

7 3.3.1 CS036 The CS036 is a 12 button keypad from Surplustraders.net. It also uses matrix-encoding. For a price of 3, this keypad is nice. However, there is no datasheet available. Because of the questionable advertisement information, this product was avoided KP-22 (chosen) The KP-22 is a 12 button keypad from All Electronics Corp. It uses matrix-encoding which was discussed as a good solution in lecture. For a price of 7.50, this keypad makes a good solution. 3.4 RS485 Transceiver The choice of transceiver depended primarily on popularity and price ISL4486 The Intersil ISL4486 would work just fine. The company is not particularly popular, but the chip costs under MAX485 (chosen) The Maxim MAX485 also will work fine. The company is very popular and the chip costs under 3. The extra dollar will be worth the likelihood that there will be fewer problems with a Maxim product. 4 List of Components The following list shows our four major devices first, then the currently planned selection for other minor components below. Name Vendor Part Number Unit Cost Quantity Cost Rabbit RCM3700 Rabbit RabbitCore Semiconductor RCM Atmel ATMEGA16- ATMega16 Futurlec 16PC Button Keypad All Electronics Corp KP Maxim RS-485 Transceiver Maxim MAX Segment LED Digital Display Radioshack Page 7 of 8

8 85dB Piezo Buzzer Radioshack key encoder Fairchild MM74C922N SPDT RELAY BOARD Smarthome Total Cost List of References DS80C400: RCM2200: ersmanual/rc2000um.pdf RCM3700: PIC16C63A: f ATmega16L: CS036: KP-22: ISL4486IB: MAX485: Page 8 of 8