BeagleBone Weather Cape. System Reference Manual - PDF

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BeagleBone Weather Cape System Reference Manual Revision A August 1st, 2012 THIS DOCUMENT This work is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License. To view a copy of
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BeagleBone Weather Cape System Reference Manual Revision A August 1st, 2012 THIS DOCUMENT This work is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License. To view a copy of this license, visit or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA. All derivative works are to be attributed to BeagleBoardtoys.com. For more information, see For any questions, concerns, or issues submit them to BEAGLEBONE WEATHER CAPE DESIGN These design materials referred to in this document are *NOT SUPPORTED* and DO NOT constitute a reference design. Only community support is allowed via resources at Beagleboardtoys.com/support THERE IS NO WARRANTY FOR THE DESIGN MATERIALS, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE DESIGN MATERIALS AS IS WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE Page 2 of 25 ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE DESIGN MATERIALS IS WITH YOU. SHOULD THE DESIGN MATERIALS PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. We mean it; these design materials may be totally unsuitable for any purposes. Page 3 of 25 BeagleBoardToys provides the enclosed product(s) under the following conditions: This evaluation board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION PURPOSES ONLY and is not considered by BeagleBoardtoys.com to be a finished endproduct fit for general consumer use. Persons handling the product(s) must have electronics training and observe good engineering practice standards. As such, the goods being provided are not intended to be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including product safety and environmental measures typically found in end products that incorporate such semiconductor components or circuit boards. This evaluation board/kit does not fall within the scope of the European Union directives regarding electromagnetic compatibility, restricted substances (RoHS), recycling (WEEE), FCC, CE or UL, and therefore may not meet the technical requirements of these directives or other related directives. Should this evaluation board/kit not meet the specifications indicated in the User s Guide, the board/kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user indemnifies BeagleBoardtoys.com from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES. BeagleBoardtoys.com currently deals with a variety of customers for products, and therefore our arrangement with the user is not exclusive. BeagleBoardtoys.com assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or services described herein. Please read the User s Guide and, specifically, the Warnings and Restrictions notice in the User s Guide prior to handling the product. This notice contains important safety information about temperatures and voltages. For additional information on BeagleBoardtoys.com environmental and/or safety programs, please contact visit BeagleBoardtoys.com. No license is granted under any patent right or other intellectual property right of BeagleBoard.org covering or relating to any machine, process, or combination in which such BeagleBoardtoys.com products or services might be or are used. Mailing Address: Beagleboardtoys.com 1380 Presidential Dr. #100 Richardson, TX U.S.A. Page 4 of 25 WARRANTY: The BeagleBone Weather Cape is warranted against defects in materials and workmanship for a period of 90 days from purchase. This warranty does not cover any problems occurring as a result of improper use, modifications, exposure to water, excessive voltages, abuse, or accidents. All boards will be returned via standard mail if an issue is found. If no issue is found or express return is needed, the customer will pay all shipping costs. Before returning the board, please visit Beagleboardtoys.com/support To return a defective board, please request an RMA at Page 5 of 25 Table of Contents FIGURES... 7 TABLES INTRODUCTION CHANGE HISTORY CHANGE HISTORY BEAGLEBONE WEATHER CAPE OVERVIEW DESCRIPTIONS IN THE BOX GETTING STARTED REPAIRS FEATURES AND SPECIFICATIONS KEY COMPONENT LOCATIONS TEMPERATURE AND BAROMETRIC PRESSURE SENSOR RELATIVE HUMIDITY AND TEMPERATURE SENSOR AMBIENT LIGHT SENSOR EXPANSION HEADER POWER INDICATOR MECHANICAL SPECIFICATIONS ELECTRICAL SPECIFICATIONS SYSTEM ARCHITECTURE AND DESIGN SYSTEM BLOCK DIAGRAM TEMPERATURE AND BAROMETRIC PRESSURE SENSOR RELATIVE HUMIDITY SENSOR AMBIENT LIGHT SENSOR EEPROM EEPROM Address I2C Bus MECHANICAL INFORMATION DESIGN MATERIALS...25 Page 6 of 25 Figures Figure 1. The BeagleBone Weather Cape Figure 2. Key Components Figure 3. BeagleBone Weather Cape High Level Block Diagram Figure 4. BMP085 Block Diagram Figure 5. Barometric pressure sensor Schematic Figure 6. RH sensor Schematic Figure 7. Ambient light sensor Schematic Figure 8. BeagleBone Weather Cape EEPROM Figure 9. BeagleBone Weather Cape Dimensions Drawing Tables Table 1. Change History Table 2. BeagleBone Weather Cape Features Page 7 of 25 NOTES Page 8 of 25 1.0 Introduction This document is the System Reference Manual for the BeagleBone Weather Cape, an add-on board for the BeagleBone. This document is intended as a guide to assist anyone purchasing or who are considering purchasing the board to understand the overall design and usage of the BeagleBone Weather Cape from the system level perspective. The design is subject to change without notice as we will work to keep improving the design as the product matures. The key sections in this document are: Section 2.0 Change History Provides tracking for the changes made to the System Reference Manual. Section 3.0 Overview This is a high level overview of the BeagleBone Weather Cape. Section 4.0 Features and Specification Provided here are the features and electrical specifications of the board. Section 5.0 System Architecture and Design This section provides information on the overall architecture and design of the BeagleBone Weather Cape. This is a very detailed section that goes into the design of each circuit on the board. Section 6.0 Mechanical Information is provided here on the dimensions of the BeagleBone Weather Cape. Section 7.0 Design Materials This section provides information on where to get the design files. Page 9 of 25 2.0 Change History 2.1 Change History Table 1 tracks the changes made for each revision of this document. Table 1. Change History Rev Changes Date By A Initial release. 08/01/2012 BBT. Page 10 of 25 3.0 BeagleBone Weather Cape Overview 3.1 Descriptions The BeagleBone Weather Cape provides weather data for the BeagleBone including temperature, barometric pressure, humidity, and ambient light. These weather input data can be accessed via I2C bus. The BeagleBone Weather Cape also features an LED to indicate that power is applied. Figure 1 below is a picture of the board. Figure 1. The BeagleBone Weather Cape Page 11 of 25 3.2 In The Box The final packaged BeagleBone Weather Cape Rev A1 product will contain the following items: - 1 BeagleBone Weather Cape - 1 Wiki information card 3.3 Getting Started Following the instructions below to start using your BeagleBone Weather Cape: 1) Mount the BeagleBone Weather on top of BeagleBone 2) Make sure the micro SD card using with BeagleBone has latest Angstrom image. 3) Power up the BeagleBone using a 5V DC power supply. 4) Connect the BeagleBone to a computer via USB cable. 5) Open a Terminal application (Teraterm, Hyperterminal, etc) and open a new connection with following settings: baud rate , data 8 bit, parity none, stop 1 bit, flow control none. 6) You should see an Angstrom log in prompt on the terminal window. If not, press Enter to show the log in prompt 7) Run the following command to display the outputs of all sensors: for sensor in /sys/devices/platform/omap/omap_i2c.3/i2c-3/*/*_input ; do echo -n $(basename $sensor): ; cat $sensor ; done 8) You should see something like this on the terminal window: lux1_input: 27 humidity1_input: temp1_input: pressure0_input: temp0_input: 270 9) The I2C outputs are interpreted as 27 lux, 38% humidity, 27 degrees C and 1013 millibar. Page 12 of 25 3.4 Repairs If you feel the board is in need of repair, follow the RMA Request process found at Do not send the board in for repair until an RMA authorization has been provided. Do not return the board to the distributor unless you want to get a refund. You must get authorization from the distributor before returning the board. Page 13 of 25 4.0 Features and Specifications This section covers the specifications of the BeagleBone Weather Cape and provides a high level description of the major components and interfaces that make up the board. Table 2 provides a list of the BeagleBone Weather Cape s features. Table 2. BeagleBone Weather Cape Features Sensor Data Temperature (operating range: 0 65 o C) Barometric pressure ( hpa or millibar) Humidity (0 100 % RH) Ambient light Data Interface Two-wire Power 3.3 V via expansion header Indicator Connectors Power LED Two 46-position connectors One 10-position connector Page 14 of 25 4.1 Key Component Locations Figure 2 shows the location of the key components on the board. Figure 2. Key Components 4.2 Temperature and Barometric pressure sensor The BeagleBone Weather Cape uses the BMP085 to measure the temperature and barometric pressure. BMP085 is an ultra-low power barometric pressure sensor capable of measuring between 300 and 1100 hpa (or millibar) and providing an output data in steps of 0.01 hpa. It can also measure the temperature between 0 and 65 C at 0.1 o C resolution. BMP085 has a flexible supply voltage range, provides low noise measurements at high accuracy via two-wire interface. 4.3 Relative humidity and Temperature sensor The BeagleBone Weather Cape utilizes the RH sensor SHT21 to measure the relative humidity. SHT21 is operating between 0 and 100% RH and -40 and 125 C and is capable of providing an output resolution at 0.04 % RH and 0.01 o C. SHT21 has a small footprint, Page 15 of 25 requires low power consumption, and transmits data digitally to BeagleBone via I2C interface. 4.4 Ambient light sensor The BeagleBone Weather Cape captures ambient light data using an ambient light sensor TSL2550. TSL2550 features two photodiodes, an analog-to-digital (ADC) converter and transmits ambient light measurements over a two-wire SMBus serial interface. The ambient light data is provided in Lux, which is a commonly used illuminance unit. 4.5 Expansion Header There are three stackable connectors on the BeagleBone Weather Cape. The 46-position and 20-position connectors will stack on top of the expansion connectors of BeagleBone. The 10-position connector will stack on top of the backlight expansion connector of BeagleBone. 4.6 Power Indicator The BeagleBone Weather Cape features an LED to indicate that power is applied to the cape. This LED is green when lit. Page 16 of 25 4.7 Mechanical Specifications Size: 4.00 x 2.50 Layers: 4 PCB thickness:.062 RoHS Compliant: Yes 4.8 Electrical Specifications Table 3 is the electrical specification of the external interfaces to the BeagleBone Weather panel. Table 3. BeagleBone Weather Electrical Specifications Specification Min Typ Max Unit Power Input Voltage DC 3.3 V Environmental Temperature range C Page 17 of 25 5.0 System Architecture and Design This section provides a high level description of the design of the BeagleBone Weather Cape and its overall architecture. 5.1 System Block Diagram Figure 3 is the high level block diagram of the BeagleBone Weather Cape. Figure 3. BeagleBone Weather Cape High Level Block Diagram Page 18 of 25 5.2 Temperature and Barometric Pressure Sensor The BMP085 uses piezo-resistive technology to provide high accuracy measurements. Temperature and pressure data can be sampled up to 128 samples per second and are converted digitally via an ADC before being transmitted over I2C interface. The output data is provided in o C and hpa (millibar) using calibration data stored inside BMP085 EEPROM. Figure 4 shows a high-level block diagram for BMP085. Figure 4. BMP085 Block Diagram The BMP085 is powered by the power rail VDD_3V3 and transmits sensor measurements to the BeagleBone via I2C2 bus. The I2C2 data and clock signals can be accessed at pin 19 and 20 of connector P2. BMP085 also features an active low master clear input (XCLR) to reset the device and an end of conversion output (EOC) to check whether the conversion is complete. These two pins are left floating on the BeagleBone Weather Cape. Figure 5 below shows the BMP085 in the BeagleBone Weather Cape schematic. Page 19 of 25 Figure 5. Barometric pressure sensor Schematic 5.3 Relative humidity sensor The SHT21 uses a generation 4C CMOSens chip to provide reliable and precise relative humidity measurements. Temperature sensor and capacitive humidity sensor are integrated into a single unit on CMOSens chip along with a signal amplifier unit, ADC, OTP memory and a digital processing unit. Relative humidity and temperature data are transmitted at respectively 12-bit and 14-bit resolution to BeagleBone over I2C2 bus. These output data are calculated in o C and %RH. SHT21 is powered by the power rail VDD_3V3 on the Weather Cape. Figure 6 below shows SHT21 on the Weather Cape schematic. Page 20 of 25 Figure 6. RH sensor Schematic 5.4 Ambient light sensor The TSL2550 features two photodiodes and an ADC on a single CMOS integrated circuit to provide 12-bit light measurements. Ambient light is converted into currents by the photodiodes and eventually to digital outputs by the ADC. One photodiode of TSL2550 is sensitive primarily to infrared light; therefore, the digital output from this photodiode is used to compensate the infrared effect on the digital output of the other photodiode, which is sensitive to both visible and infrared light. The final output data calculated in a commonly used illuminance unit of Lux. These data are transmitted to BeagleBone via I2C2 bus. TSL2550 is powered by the power rail VDD_3V3. Figure 7 shows the TSL2550 in the BeagleBone Weather Cape schematic. Page 21 of 25 Figure 7. Ambient light sensor Schematic 5.5 EEPROM The BeagleBone Weather Cape has an EEPROM containing information that will allow the SW to identify the board and to configure the expansion headers pins as needed. EEPROMs are required for all Capes sold in order for them to operate correctly when plugged in the BeagleBone. The EEPROM used on this cape is the same one as is used on the BeagleBone, a CAT24C256. The CAT24C256 is a 256 kb Serial CMOS EEPROM, internally organized as 32,768 words of 8 bits each. It features a 64-byte page write buffer and supports the Standard (100 khz), Fast (400 khz) and Fast-Plus (1 MHz) I2C protocol. Figure 8 is the design of the EEPROM circuit. Page 22 of 25 Figure 8. BeagleBone Weather Cape EEPROM EEPROM Address In order for each Cape to have a unique address, a board ID scheme is used that sets the address to be different depending on the order in which it is stacked onto the main board. A two position dipswitch or jumpers is used to set the address pins of the EEPROM. It is the responsibility of user to set the proper address for each board. Address line A2 is always tied high. This sets the allowable address range for the expansion cards to 0x54 to 0x57.All other I2C addresses can be used by the user in the design of their Capes. But, these addresses must not be used other than for the board EEPROM information I2C Bus The EEPROMs on each expansion board is connected to I2C2. For this reason I2C2 must always be left connected and should not be changed by SW to remove it from the expansion header pin mux. The I2C signals require pull-up resistors. Each board must have a 5.6K resistor on these signals. With four resistors this will be an affective resistance of 1.4K if all Capes were installed. Page 23 of 25 6.0 Mechanical Information This section provides information on the mechanical aspect of the BeagleBone Weather Cape. Figure 9 is the dimensions of the BeagleBone Weather Cape. Figure 9. BeagleBone Weather Cape Dimensions Drawing Page 24 of 25 7.0 Design Materials Design information can be found at BeagleBoardToys wiki: Provided there is: - Schematic in PDF - Schematic in OrCAD - Manufacturing files o PCB Gerber o PCB Layout (Allegro) - Bill of Materials - System Reference Manual (This document) These design materials are *NOT SUPPORTED* and DO NOT constitute a reference design. Only community support is allowed via resources at BeagleBoard.org/discuss. THERE IS NO WARRANTY FOR THE DESIGN MATERIALS, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE DESIGN MATERIALS AS IS WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE DESIGN MATERIALS IS WITH YOU. SHOULD THE DESIGN MATERIALS PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. We mean it, these design materials may be totally unsuitable for any purposes. Page 25 of 25
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