PROJECT DESCRIPTION WWU Engineering Technology 2015 Senior Design Project By: Isaiah Ryan

Transcription

1 PROJECT DESCRIPTION WWU Engineering Technology 2015 Senior Design Project By: Isaiah Ryan

2 TABLE OF CONTENTS 1. INTRODUCTION PRODUCT ELECTRICAL SPECIFICATIONS Project Specifications Power Requirements Environmental Requirements SYSTEM DESCRIPTION AND SPECIFICATIONS Hardware Block Diagram Hardware Description and Specifications MCU DC-DC Converter Bluetooth Transceiver DC Buck Regulator Voltage Divider Temperature Sensor Software Description and Specifications Programming Languages Major Code Modules Kernel Mobile App Tasks USER INTERFACE REQUIREMENTS User Interface Layout User Interface Description DEVELOPMENT PLAN Prioritized List of Features Description and Schedule of Development Tasks Required Hardware and Software Development Tools Safety Plan Demonstration Prototype and Materials Description PRELIMINARY PARTS LIST

3 1. INTRODUCTION The Wireless Controller for DC/DC Converter will allow a user on a boat to wirelessly control and monitor a DC-DC converter that uses a 12V engine battery to charge a 12V auxiliary battery. Engine batteries are not designed for low current over a long time and thus can be quickly drained by equipment such as fish finders, GPS, lights, etc. Auxiliary batteries are used for this reason, but with standard chargers that use shore power, auxiliary batteries cannot be recharged at sea. The product solves the need to return to shore by charging an auxiliary battery through the engine battery with the DC-DC converter. Wireless capability provides remote access to the DC- DC converter, which must be embedded for water protection. With an app designed for a smartphone or tablet, the user will be able to enable and disable the converter, adjust the converter output settings for different battery types, and also continuously monitor voltage and current from the converter. 2. PRODUCT ELECTRICAL SPECIFICATIONS 2.1 Project Specifications Table 1 below lists key specifications required by the product: SPECIFICATIONS Max Output Current 20A Output Voltage Range 0V-15V Nominal Output Voltage 12V Output Voltage Accuracy 0.05V Input Voltage Range 9V-15V Nominal Input Voltage 12V Table 1 Standards that apply to the product are listed below: IEEE Covers methods for communicating devices in a personal area network that apply to the Bluetooth wireless protocol. IEEE 45 Covers recommended practices for electrical installations on shipboard Underwriters Laboratories (UL) 458 Contains standards for power converters/inverters and power converter/inverter systems for land vehicles and marine crafts. 2

4 2.2 Power Requirements The MCU in the product will be powered by the donor battery that supplies power to the DC- DC converter. A buck voltage regulator will lower the 12V level of the battery to the 3.3V required by the MCU and Bluetooth transceiver. Worst-case power dissipation in the product is summarized in the following Table 2. The total was increased slightly to provide a buffer for unaccounted losses: POWER DISSIPATION Source DC-DC Converter MCU Bluetooth Transceiver DC Buck Regulator Voltage Divider Resistors TOTAL Table 2 Power 15W 20mW 165mW 181mW 138mW 16W 2.3 Environmental Requirements Because the product will operate on a boat, the environmental requirements defined in IEEE standard 45: Recommended Practices for Electrical Installations on Shipboard. Applicable requirements are listed below: Max ambient temperature operation: 70 C for main/auxiliary machine space Min ambient temperature operation: -20 C Corrosion resistance: resistant to moisture and salt-laden atmosphere Unaffected by roll/pitch of a vessel underway: 22.5 roll angle and 7.5 pitch angle Resistance to vibration: vibrancy frequency range of 5-50Hz with a velocity amplitude of 20mm/s The product will meet environmental requirements by using parts that satisfy the above specifications. The electronic components can be placed in a corrosion-resistant casing for further protection. Securely fastening the product will prevent damage caused by movements of a vessel underway. 3

5 3. SYSTEM DESCRIPTION AND SPECIFICATIONS 3.1 Hardware Block Diagram A block diagram of the product hardware is shown in Figure 1 below. A description of the hardware components is included in the following pages. Bluetooth Transceiver Mobile Device 3.3V MCU MKL05Z32VFM4 Vsupply 3.3V Serial 3.3V Out Serial Comm CPU FLASH RAM Vout DC Buck Regulator Vin GPIO DAC ADC External Temp Sensor (Near Battery 2) Battery 2 Vout Voltage Divider Ven Vadj Imon Voltage Divider Voltage Divider Battery 2 Vout Battery 1 12V Vin Vout DC-DC Converter Battery 2 Figure 1 Hardware Block Diagram 3.2 Hardware Description and Specifications MCU In selecting the MCU for the product, several candidates were considered from different manufacturers including Freescale, TI, STMicroelectronics, and Silicon Labs. In terms of memory size, available peripherals, and GPIO pins, all the candidates prove to be capable. In terms of power efficiency however, Silicon Labs EFM32G200 excels above the rest and was thus chosen as the ideal MCU. But because of the high cost of Silicon Labs development boards, Freescale s MKL05Z32VFM4 MCU was chosen as a suitable replacement. Freescale has cheaper development boards and is more familiar to the student. The following Figure 2 shows the functional features of the MKL05. 4

6 Figure 2 MCU Functional Features The product does not require very high processing speeds, so the MCU system/core and bus clock frequencies should suffice. These are specified as follows: System/core clock frequency: Bus clock frequency: 48 MHz 24 MHz The program code will be stored in flash memory and shouldn t require more than 8KB. Program data will be stored in SRAM memory and shouldn t require more than 2KB. For future added product features, a Freescale MCU with more memory could be substituted if needed. The MCU memory types and sizes will work for the basic product features and are given as follows: Flash: SRAM: 32KB 4KB 5

7 The required MCU peripheral specifications for the product are listed in Table 3 below: REQUIRED MCU PERIPHERAL SPECIFICATIONS Peripheral Parameter Specification Serial Communication Number of modules 1 module GPIO Number of outputs 1 output ADC DAC Number of channels Sampling frequency Resolution Max Input Voltage Number of channels Resolution Conversion rate Table 3 MCU Functional Features The actual MCU peripheral capabilities are reported below: Serial Communication: The MCU includes one 8-bit SPI module, one low-power UART module, and one I 2 C module. Whichever of these modules is compatible with the chosen Bluetooth transceiver may be used in the product since there are no other features requiring serial communication. GPIO: The chosen MCU includes a maximum of 28 I/O pins, which is plenty for the product since the only required I/O pin is a digital output to enable or disable the DC-DC converter. The extra pins may be used to accommodate any future added product features. ADC: The ADC peripheral will be used to measure the DC-DC converter output voltage and current, the input voltage, the voltage of the auxiliary battery, and the ambient temperature via the external temperature sensor. This is why at least 5 ADC input channels are required. The MCU ADC supports up to 24 inputs so there is plenty of room for more inputs to be added in the future. The ADC can perform up to 818 ksamp/sec so the converter output voltage and current can be sufficiently monitored. This sampling frequency is also way above what is required for the temperature measurements. As for resolution, the MCU ADC provides up to 12-bit conversions, which surpasses the required product resolution of 9 bits. The ADC is not able to measure voltages above 3.3V so the converter input and output voltages and the auxiliary battery voltage must be scaled down to below 3.3V with voltage dividers. 6 5 channels 1samp/sec 9 bits 15V 1 channel 10 bits 1 conv/sec

8 DAC: The DAC peripheral will be used to adjust the DC-DC converter output voltage. It will generate an analog voltage that will be applied to a voltage-adjust pin on the converter. The minimum required resolution is possible with the MCU DAC, which has a 12-bit resolution. Charging a battery is a relatively slow process, which is why efficient charging can be achieved by updating the DC-DC converter output voltage at least once per second. This is no problem for the MCU DAC, which can perform up to 1 million conversions per second. The DAC has just one channel so it is not possible to use the DAC for added features DC-DC Converter The DC-DC converter is the electrical interface for the product because it is wired to the two external 12V batteries. Thus, its required electrical specifications match the product electrical specifications defined in Table 1. An additional requirement for the DC-DC converter is a voltage-controlled voltage adjust pin. A heat sink will most likely be installed with the DC-DC converter to dissipate heat Bluetooth Transceiver The Bluetooth transceiver will wirelessly receive messages from the mobile device and convert the messages to a serial voltage signal for the MCU. The only required specifications for the Bluetooth module are as follows: Vsupply: 3.3V Wireless range: 7 10m The required supply voltage is 3.3V because that is the supply voltage that the MCU will use also. A wireless range of 10m is sufficient for small vessels that the product is meant for DC Buck Regulator A DC buck regulator will be used to lower the 12V level of battery 1 to 3.3V for powering the MCU and Bluetooth transceiver. The following specifications are required for the buck regulator: Input voltage range: 9V 15V Nominal input voltage: 12V Output voltage: 3.3V Output voltage accuracy: 0.3V Voltage Divider A voltage divider will be used to divide down the DC-DC converter input and output voltage and the auxiliary battery voltage to valid levels for the ADC. This method works as long as the total resistance of the voltage divider is less than the specified ADC max input resistance of 5kΩ. The total resistance is calculated as the parallel resistance of the two resistors. To achieve accurate measurements, resistors must be used with a tolerance of at least.5%. Using resistor values of 4.75kΩ and 21.5kΩ yields a parallel resistance under the max resistance of 5kΩ and provides an appropriate ratio for dividing the voltage. The maximum DC-DC

9 converter output voltage will not exceed 15V, and with this resistance ratio, 15V becomes: 15V * (4.75k/21.5k) 3.13V So the divided voltage should never exceed the ADC max input voltage of 3.3V, and even if it did happen, the MCU contains protective circuitry on the ADC inputs Temperature Sensor An external temperature sensor with voltage output will be used to measure the ambient temperature. The required specifications for the temperature sensor are as follows: Output range: 0 3.3V Accuracy: 0.5 C Temperature range: -20 C 70 C 3.3 Software Description and Specifications Programming Languages All the software modules will be written in C. The MCU uses ARM M0+ as its assembly language. The mobile app will most likely be written in Java for the Android OS Major Code Modules The major required software modules to be included in the product are listed below: Main.c This module will contain the function main() where the program initializes and enters run mode. Serial.c This module will contain functions for accessing the serial communications module. Initialization code and read/write tasks will be written in this module. ADC.c This module will contain initialization and sampling tasks for the ADC module. DAC.c This module will contain initialization and conversion tasks for the DAC module Kernel Because of the relative simplicity of the software, a real-time kernel will not be used. Instead, a time-slice design will be used where the MCU will be placed in a low-power state and be periodically awoken to perform tasks such as sampling. 8

10 Mobile App Tasks The following tasks will be included in the mobile app: Setup Upon starting the mobile app, a task must initiate the interface and communication with the MCU User interface A task must handle the user interface on the mobile device. This includes displaying voltage/current data for the user, detecting button presses, and appropriately switching between interface states. Bluetooth communication Another task must handle communication with the Bluetooth transceiver connected to the MCU. 4. USER INTERFACE REQUIREMENTS 4.1 User Interface Description Figure 3 below previews how the mobile device user interface layout will appear: Enable/Disable Battery Type Select Battery Type 1 Battery Type 2 Voltage xxxxx V Battery Type N Current xxxxx A Figure 3 Mobile Device User Interface Layout The above mobile device user interface layout just shows what objects will be included in the display. It does not depict exactly how the interface will appear. At the top of the display is a button that will either enable or disable the DC-DC converter. Below the button is a menu object for selecting what battery type will be charged with the converter. The remaining objects at the bottom of the interface are display boxes for the voltage and current outputs of the DC-DC converter. 9

11 4.2 User Interface State Diagram Below in Figure 4 is a state diagram of the user interface: Start Interface Initialization Battery Type Select Enable Standby Run Disable Figure 4 State Diagram The user interface will start in an initialization state in which the display is set up and Bluetooth communication with the MCU is established. After initialization is complete, the program enters a standby state in which the user may select a battery type to charge or enable the DC-DC converter. A default battery type is selected for charging when the standby state is first entered. If a new battery type is selected for charging, the state stays in standby. If the user presses the Enable button while in the standby state, the program enters the run state in which the DC-DC converter begins operating. The user may turn off the DC-DC converter at any time by pressing the Disable button, returning the state to standby. 5. DEVELOPMENT PLAN 5.1 Prioritized List of Features The prioritized list of product features is included below from highest to lowest priority: 1. Functioning DC-DC conversion 2. Working wireless communication link between app device and MCU 3. Option to enable/disable DC-DC conversion 4. Obtaining and displaying current/voltage data from DC-DC converter 5. Option to select different battery types to charge 6. Addition of temperature sensor to adjust DC-DC conversion for temperature 7. Automatic disabling of DC-DC converter if excessive current is detected A benefit of this design is that there is a lot of room for added features. The initial product mobile app will be developed for Android OS, but later it may be ported to ios for Apple mobile devices. One added feature could be to allow user-defined charging settings for batteries to more closely match battery manufacturer recommendations. Another feature would be to allow the user to specify the voltage loss in the source wiring of the auxiliary battery to make battery voltage measurements more accurate. If faster charging were desired, a 40A DC-DC converter unit could be used with a larger heat sink or a cooling fan. 10

12 5.2 Description and Sequence of Development Tasks Table 4 below outlines the tentative weekly schedule for product development during winter and spring quarters: TENTATIVE WEEKLY DEVELOPMENT SCHEDULE Date Tasks By Jan. 4 Acquire hardware components Jan. 4 Jan. 10 Create project file in IDE, start writing startup code Jan. 11 Jan. 17 Continue writing startup code Jan. 18 Jan. 24 Write GPIO code Jan. 25 Jan.31 Start writing ADC code Feb. 1 Feb. 7 Continue writing ADC code Feb. 8 Feb. 14 Start writing DAC code Feb. 15 Feb. 21 Continue writing DAC code Feb. 22 Feb. 28 Program MCU to enable/disable DC-DC converter Mar. 1 Mar. 7 Program MCU to change DC-DC converter voltage Mar. 8 Mar. 14 Work on measuring voltage/current with MCU Mar. 15 Mar. 21 Continue working on measuring voltage/current Mar. 22 Mar. 28 Start building mobile app Mar. 29 Apr. 4 Continue working on mobile app Apr. 5 Apr. 11 Continue working on mobile app Apr. 12 Apr. 18 Add DC regulator to power MCU and Bluetooth Apr. 19 Apr. 25 Work on Bluetooth communication *Hardware Reviews* Apr. 26 May 2 Continue to work on Bluetooth *Hardware Reviews* May 3 May 9 Continue to work on Bluetooth May 10 May 16 Add temperature sensing feature May 17 May 23 Apply finishing touches *Code Reviews* May 24 May 30 Prepare for demos *Code Reviews* May 31 Jun. 6 Demos Table 4 Tentative Weekly Schedule 11

13 After acquiring the hardware components, the first task in the development schedule is to create a project file in the IDE and start writing the MCU startup code. Before any further project development, it is necessary to be able to compile a project, build the project, and load it into the MCU flash. This will be the focus of the first few weeks of January. Once the project can be loaded into the MCU, the ADC and DAC code will be written so that the MCU can interface with the DC-DC converter. Once the ADC and DAC are functioning, the code will be written for enabling/disabling the converter, changing the converter output voltage, and then measuring the DC-DC converter output voltage/current. At this point, it will be time to start working on communication with a mobile device. This will first require building the mobile app. Once the app is built, the Bluetooth communication will be established between the mobile device and the MCU. Finally, the temperature sensing feature will be added and finishing touches will be applied so that preparation can be made for the demo. 5.3 Required Hardware and Software Development Tools Hardware development tools will include the following: Power supply for powering the MCU and simulating a 12V battery Oscilloscope or multimeter for measuring voltages A smartphone for running the mobile app Kinetis Freedom development board for prototyping Software development tools will include the following: Kinetis Development System (KDS) IDE for MCU software development Android Studio for mobile app development 5.4 Safety Plan High voltage does not pose a danger in this product since voltages higher than 15V will not be present. Still, proper precaution will be taken when wiring components by making sure the power supply is disconnected. When using real 12V batteries, proper precaution will be taken to avoid battery-related accidents such as acid exposure or battery explosion. 5.5 Demonstration Prototype and Materials Description The product prototype will be demonstrated using one of Freescale s Freedom development boards, the FRDM-KL05Z. To construct the product, parts will be either soldered or wirewrapped. If possible, the product electrical components will be enclosed inside a case since the actual product would have to be protected from the environment. For demonstration, a 12V engine starting battery and 12V auxiliary, deep-cycle battery will be needed. A load will be applied to discharge the deep-cycle battery so that charging can take place. In addition, either a smartphone or tablet device will be used to run the mobile app. Posters will be constructed that introduce the product and explain its significance. 12

14 6. PRELIMINARY PARTS LIST Table 5 below shows the preliminary parts list for the product (resistors not included): PRODUCT PRELIMINARY PARTS LIST Part Part # Cost Lead Time Power Dissipation MCU MKL05Z32VFM4 $ days 20mW DC-DC Converter NQ20x20ETx20 $ days 15W DC Buck Regulator LM2596 $ days 181mW Temperature Sensor LMT84-Q1 $ days 0.018mW Bluetooth Module RN-42 $ days 165mW Table 5 Preliminary Parts List 13