System Specifications /
11/13/2012 /
Prepared by:
Chad Holst
Design Engineer
Crystal So
Design Engineer
Rebecca Steffenson
Design Engineer
The System Specifications documents our selection of an alternative for each block and the reasoning is justified. Each block in our design contains a general description and discusses topics such as acceptance tests, testing philosophy, and manufacturing costs. The Project Plan document is referred to, which is submitted in conjunction to this document./
Table of Contents
I.Problem Statement and Overall Design Goal
II.Alternatives Considered and Chosen
III.System Block Diagram
IV.Operating Environment
V.Power Supply Block
i. General Description
ii. Specifications of Physical Properties
iii. Testing Philosophy
iv. Acceptance Tests
v. Specification of Reliability
vi. Specification of Maintainability
vii. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
viii. Manufacturing Costs
ix. Criteria for Determining Manufacturing Costs
VI.LED Mounting Dock Block
i.General Description
iii. Specifications of Physical Properties
iii. Testing Philosophy
iv. Acceptance Tests
v. Specification of Reliability
vi. Specification of Maintainability
vii. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
viii. Manufacturing Costs
ix. Criteria for Determining Manufacturing Costs
VII.Sensor Array Block
i. General Description
ii. Specifications of Physical Properties
iii. Testing Philosophy
iv. Acceptance Tests
v. Specification of Reliability
vi. Specification of Maintainability
vii. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
viii. Manufacturing Costs
ix. Criteria for Determining Manufacturing Costs
x. Operating Environment
VIII.Raspberry Pi Block......
i. General Description
ii. Specifications of Physical Properties
iii. Testing Philosophy
iv. Acceptance Tests
v. Specification of Reliability
vi. Specification of Maintainability
vii. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
viii. Manufacturing Costs
ix. Criteria for Determining Manufacturing Costs
IX.Excel Program Block
i. General Description
ii. Testing Philosophy
iii. Acceptance Tests
iv. Specification of Reliability
v. Specification of Maintainability
vi. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
vii. Manufacturing Costs
viii. Criteria for Determining Manufacturing Costs
X.Development Costs
Bibliography
Appendix A: Current Calculations (Mounting Dock Supply Block)
Appendix B: Functional Block Diagram (Sensor Array Block)
Appendix C: Pull-Up Resistor Graph (Sensor Array Block)
Table of Figures
Figure 1: System Block Diagram
Figure 2: Power Supply Block
Figure 3: Block Diagram for Power Supply Testing System
Figure 4: Mounting Dock Diagram
Figure 5: Potentiometer Voltage Divider
Figure 6: Block Diagram of Mounting Dock Testing System
Figure 7: TSL2561T Digital Lux Sensor
Figure 8: Pull-Up Resistor Circuit
Figure 9: Block Diagram of Sensor Array Testing System
Figure 10: Raspberry Pi Circuit Diagram
Figure 11: Block Diagram of Raspberry Pi Testing System
Figure 12: Block Diagram of Excel Testing System
I.Problem Statement and Overall Design Goal
Our customer, the Mine Supply Company, brings in LEDs from overseas manufacturers and mounts them in casings designed for use in a mining environment, which they then sell to mines all over the world. These lights have no set standard of lumen or lux measurements, nor any documentation of light output spread over a set area. To create this documentation for their customers, the Mine Supply Company has been testing its products by using a handheld lumen reader in a dark field to obtain data on these imports. This procedure is error prone due to ambient light and the difficulty of working in a dark field at night.
Our basic goal is to design a testing system that will be easier, more efficient, and less error prone than the Mine Supply Company’s current testing system, and will be able to graphically display the lumens of the light being tested.
II.Alternatives Considered and Chosen
Our design has five main blocks, two (Power Supply and LED Mounting Dock) of which had no serious alternatives discussed since they are relatively simple and straightforward blocks. Each of our other blocks had at least two alternatives for consideration.
The choices for the Data Collection block were a PIC microcontroller and a Raspberry Pi microcontroller. As each microcontroller meets our needs as discussed in the Requirements Specificationdocument, we chose the Raspberry Pi since it would be easier to trouble shoot any data issues using this microcontroller.
For the Sensor Array block we considered three different sensor layouts. The first option was a large sensor grid over the entire illuminated area. This made foran easy testing procedure, but required the highest cost and a difficulty set up. The second option considered used a smaller grid of sensors that would be moved over the test area during the test procedure. This had the advantage of using fewer sensors, but involved a difficult procedure to test a light. The last option was the successful alternative;it is a line of sensors where the light being tested would sit at the end of the row of sensors, and be rotated past the line, giving data over the full lit area.
Our last choice was for the Data Manipulation block. Here, we considered three programs for graphing, manipulating and displaying data which all met our needs: Java, Matlab, and Excel. We chose Excel since the customer already has experience and access to this program.
III.System Block Diagram
To meet our customer’s desire for a better LED testing system, we have designed with the followingsystem (Figure 1) as a block diagram for our LED test system.
The Power Supply block will take in standard wall voltage and supply the required DC voltage to the LED, Raspberry Pi, and Sensor Array blocks.
The LED Mounting Dock houses the light to be tested. This light will be shined onto the Sensor Array. This block will also allow the light to be rotated past the line of sensor to obtain a full set of data and record the light intensity with the angle of the light.
The Sensor Array block will consist of a line of lux sensors that will output values to the Raspberry Pi. Before values are gathered for the LED to be tested,the sensors will report the amount of ambient light so it can be accounted for in the Excel Program.
The Raspberry Pi will gather values from the Sensor Array block and determine what angle those values are at based on the signal from the LED Mounting Dock. These values and angles will be sent to the computer and stored as a .csv file.
The Excel program will be used by the client to produce the desired results. They will have the options to display and/or store the graphical and tabular data from the LED being tested. These values will have the pre-test values for ambient light subtracted from the test values. The graph displayed will also be able to compare the difference in the light spreads of the two LEDs.
IV.Operating Environment
The operating environment of the system is the same for all blocks, though the environment is more carefully considered in certain blocks.These will be discussed further in the block descriptions later.The temperature in the operating environment will ideally beroom temperature, between 18-24°C because that is the average comfortable indoor range for adults to work in. The temperature will depend on the location of where the customer chooses to test the LEDs because they may decide to rent a school gym to use our system, and school gyms may have set lower temperatures, but will only be a few degrees difference.The ideal indoor relative humidity levels in Canada are 35% (winter)to 50% (summer). However, humidity is lower in Saskatchewan because the province has a drier climate. An indoor environment for this system also means with all doors and windows closed to reduce ambient light. This specified operating setting would be ideal for the customer, and all of the blocks will work in this environment.
V.Power Supply Block
i. General Description
The power supply block has an input of 120Vac and outputs24and 3.3Vdc. The maximum expected draw for current is less than 3A from the 120Vac supply. The Power Supply Block consists of a power supply provided from our client which converts the 120 Vac to 24 Vdc with a 1A capacity and a micro USB converter for the Raspberry Pi. The 24Vdc output from the client’s power supply is stepped down to 3.3Vdcusing a linear voltage regulator for other blocks in our design. A circuit diagram for the Power Supply Block can be seen in Figure 2.
This block requires one source of power for the LED andanother for the potentiometer. The light is supplied by the 24Vdc power supply and requires no more than 500mA, and the potentiometer is supplied with 3.3Vdc. The 3.3Vdcis stepped down from the 24Vdc using a LT1086 linear voltage regulator from Linear Technology. The Sensor Array block requires a voltage between 2.7-3.6Vdc,supplied by the linear regulator. One regulator is used because it can supply 1.5A,and the sensors and potentiometer combined require a maximum of 6.1mA.
ii. Specifications of PhysicalProperties
The Power Supply Block’s size isminimal to fit on the LEDMounting Dock along with the Raspberry Pi to supply power to all the circuits. The size of the client-supplied power supply is approximately 5cm X 5cm X 5cm, which is the majority of the size of this block.
iii. Testing Philosophy
The analysis test for this block will consist of two parts (see Figure 3). First, a circuit diagram will be analyzed to ensure that the block has no obvious faults, and will ensure theoretical operation of the design. Once the block is built,it will be tested using voltmeters and ammeters. All voltages will be checked using a calibrated voltmeter, both at zero current draw and max current draw. Max current draw will be obtained by using a load resistor to test that the output voltages do not vary outside the next blocks' error margins. This analysis is expected to take four to six hours.
iv. Acceptance Tests
This block will be successful if it produces the required voltage for the output without a change in voltage of more than 10% during changes of load.
v. Specification of Reliability
This block is able to supply power to each other block regardless of conditions. This requires the block to supply a minimum of 3A of current total to the entire system at room temperature in indoor settings.
vi. Specification of Maintainability
The Power Supply Block requires minimal maintenance. Once this block is functional and passes the acceptance tests, there will be no maintenance issues.
vii. Acceptance Tests Testing Philosophy for Reliability and Maintainability
The Power Supply Block will be tested for 10 minutes to maintain an output current of 3A to a load. If the system is capable of providing power for this duration of time at the desired voltages, the system passes its reliability and maintainability requirements.
viii. Manufacturing Costs
The cost of components for this block will only consist of the voltage regulator which comes to $2.90 for the whole block. The rest of the components are either supplied by the client or the cost is included with the purchase of a component from another block (as with the power supply for the Raspberry Pi).
ix. Criteria for Determining Manufacturing Costs
Manufacturing costs were determined by the cost of components required for the block.
VI.LED Mounting Dock Block
i.General Description
The purpose of the LED Mounting Dock block is to mount and stabilize the LED to be tested; the Mine Supply Company provides the LED and we will build the mounting dock. Since the operating environment of the system is indoors, the mounting dock will not need to account for various weather conditions such as rain and wind.
The LED to be tested has various base dimensions and comes with a fixture, provided by the customer. One LED provided by the customer has a square dimension of 4.5cm X 1.9cm, while another is 10.2cm X 3.8cm. As shown in Figure 4, the LED will sit on a circular platform of a larger diameter so it is more stable. The circular platform sits about halfway into the larger rectangular base, and is rotatable so that the LED can be rotated for testing. There is a small slot drilled into the bottom of the circular platform (as well as the rectangular base), where a potentiometer of 1k (RHS1K0E-NDfrom Digi-Key) will fit. The potentiometer will have an input voltage of 3.3V and the analog output voltage which the Raspberry Pi block converts to an angle.
The LED Mounting Dock will rest on a table and the center of the LED to be tested will be about 100cm high, measured from the ground, which is about how high the sensors will be placed. If adjustments for a higher dock need to be made it will be easy for the customer to add, for example, a block of wood between the LED to be tested and the circular platform.
The output of the LED Mounting Dock block is an analog voltage from the potentiometer paired with a voltage divider to keep the current low. Since the potentiometer is 1k, the load resistance is determined to be 10k because it should be large compared to the potentiometer. The maximum current through the circuit would be <3.7mA with a load resistance (see Appendix A for the calculation).
iii. Specifications of Physical Properties
The size dimensions of the mounting dock are shown in Figure 4. The circular platform is 15cm in diameter, and the rectangular base is 45cm X 25cm X 25cm. The circular platform is larger than base size of the customer's largest fixture to help with stability. The size of the dock allows it to sit on a standard table. The weight is less than 5kg, so the client can move it easily over a short distance.
iii. Testing Philosophy
The testing philosophy for this block mainly consists of physical tests over theoretical. We will start from the top to the bottom since the LED has a set base size. The circular platform will be built first, followed by the rectangular platform. Each platform must be able to bear the weight of the parts that sit on top of it. As well, we will test the potentiometer by moving the circular platform and ensuring the potentiometer outputs changes in analog voltage.
iv. Acceptance Tests
This block will be successful if the mounting dock is stable and the potentiometer is outputting analog voltages when the circular platform is rotated.
v. Specification of Reliability
The block is reliable if the potentiometer consistently outputs the same analog voltages, plus or minus 10%, at the same angle. Various tests will be done at different angles.
vi. Specification of Maintainability
The LED Mounting Dock block does not require maintenance unless the potentiometer becomes inaccurate over time, the wood wears from too many rotations of the circular platform, or other uncontrolled aspects such as moisture seeping into the wood.
vii. Acceptance Tests & Testing Philosophy for Reliability and Maintainability
This block will be tested over an hour to ensure that the potentiometer outputs the same analog voltages, plus or minus 10%, at the same angle. Over time, the voltages should not be outside of the range.
viii. Manufacturing Costs
The cost of the parts of the LED Mounting Dock block includes the potentiometer, which will cost $43.44, and the wood, which costs about $20.The total manufacturing cost is $63.44.
ix. Criteria for Determining Manufacturing Costs
The manufacturing costs consist of the costs of the parts to build it, including the wood and the potentiometer.
VII.Sensor Array Block
i. General Description
The Sensor Array block consists of using ten sensors in a vertical line in front of the LED to be tested. The first sensor is mounted 5 meters away, facing the light to be tested. The next sensor is 5 meters behind the first sensor, though raised a bit higher so that the first sensor does not block light to the second, or any blocking of light is negligible. Ten sensors are used in this configuration with the test area being 50 meters. The LED to be tested is rotated 180 degrees (at 90 degrees when facing the sensors directly).
We chose the TSL2561T digital lux sensor from Texas Advanced Optoelectronic Solutions for the ten sensors. The lux sensor can be seen in Figure 7. The sensor has a high lux range with a maximum of 40,000 lux and requires an input voltage range of 2.7-3.6V, which will be from inputted from the Power Supply block. The supply current is rated at a maximum of 0.6mA and the digital output current is rated at a maximum of 20mA.The TSL2561 sensor contains two integrating ADC converters that integrate the currents from two channels of photodiodes (channel 0 and 1).
The functional block diagram provided in the component's datasheet can be viewed in Appendix B. The lux sensor has a two-wire serial interface which uses a I2C bus. The I2C bushas a serial data line (SDA) and a serial clock (SCL). These lines will be connected across all ten sensors. The data from each sensor will travel on the bus to the Raspberry Pi, and the timing must be set correctly in the code such that only data from one sensor will be transferred at a time.
The power supply lines must be decoupled with a 0.1F capacitor as specified by the data sheet. The capacitor is placed close to the sensor because it will provide a low impedance path to ground at high frequencies to handletransient current caused by the internal logic switching. The pull-up resistors are determined by the bus capacitance, and they ensure the signals are pulled high within the required rise time. At this time, the bus capacitance cannot be calculated, but if the value is assumed to be 100pF, then the resistor isabout 4.7k (refer to Appendix C).