Spring 2018: Micro FOBO Mechanical Designs

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By: Miguel Gonzalez (Project Manager & Manufacturing)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Notice

In this blog post, you will learn about initial mechanical designs for the Micro FOBO. We will discuss our thought process for each design component and relate it back to the customer’s requirements. Note that this the first post for the mechanical drawings of the miniaturized FOBO design created by Jonathan Dowdall. New advances in construction and design of the robot will be updated in a future post and linked at the bottom of this page. It is important to note the models shown in this post have yet to be physically tested. But plans to 3D print them have been made and the parts will be tested together. All results will be posted in a follow-up update blog post detailing our results of the models introduced here.

Introduction

The ROFI and FOBO bipeds can be considered as aging robots in which the designs have been used in many occasion for EE 400D projects. This can be particularly helpful if new students like ourselves would like to make such robots, considering resources for these models are plentiful on Arxterra.com. Unlike previous semesters our biped design will not encapsulate the same model but instead be a miniaturized version of those robots. Our group will particularly focus on the FOBO design by Jonathan Dowdall which is found on projectbiped.com. The miniaturized FOBO will be much smaller than the original approximately 60 percent its size and be controlled via micro servos (SG90S). We hope that in miniaturizing the design we can achieve a more efficient way of making the robot walk, turn, and avoid obstacles; all which are some design criteria for the maze.

Related Requirements

Level One Requirements

L1-3: Micro FOBO will have 2 legs.

L1-4: Micro FOBO will be a toy robot based on the design of the FOBO by Jonathan Dowdall.

L1-11: Micro FOBO shall be 60% or less of the overall size of Jonathan Dowdall’s FOBO

Level Two Requirements

L2-2: Micro FOBO dimensions will need to be small enough to fit in a 4in by 4in box for maze purposes.

L2-14: Micro FOBO shall measure within 4.5” x 3.25” x 7.25”.

Micro FOBO Design

For some clarification and for better understanding our design of the Micro FOBO, I have created a color-coded assembly of the robot with matching titles indicating the names of each component. Below I discuss the design of these components that make up the Micro FOBO.

 

Fig.1 Micro FOBO Colored Parts

As you can see from the image above, the Micro FOBO consist of 9 different parts: Servo Hip, Foot, Servo Band, Servo Bracket, Servo Wrap, Bearing Frame, Body Riser, Electronics Frame, and the Head. Note that Micro FOBO can be made up of multiple copies of the same part component and thus colored coded with the same color. For example, there are four servo bands in Micro FOBO which are shown in light green on the picture. Now that we know which parts make up the robot we can begin looking at the design of each part individually.

Part 0: Servo Hip

Fig.2 Servo Hip

The “Servo Hip” component of the Micro FOBO is responsible for attaching the two upper micro servos which are the hip servos. This bracket connects both servos (right and left legs) together to act as a hip bone that allows the robot to move its legs left to right. The connection to the servos is made via servo horns that are provided by the manufacturer. This part has two allocated trenches that match the dimensions of the servo horns allowing the servos to mount to the part. The horns are then screwed onto the servo hip using M2.5 screws that are 8mm in length.

Drawing File

Part 1: Foot

Fig.3 Foot

The “Foot” component is the same for both legs and is a simple shoe like design with wide pads on its sides. The extra material on the sides allows a greater amount of surface to touch the floor allowing the robot to balance easier. Currently, this part is in its simplified state as there is not much detail design put on it. This is because the team plans on mounting UV sensors onto the bottom of the foot where the hole is located. This would allow the sensor to be as close to the ground as possible to maintain an accurate reading. Once we receive the sensor additional design changes will be made to this part. Currently, the part allows the ankle servo, which is the servo closest to the ground, to be mounted onto one side of the foot though servo horn cutouts. The horn cutout is located on the inside wall of the part. The hole then allows an M2.5 X8 screw to secure the servo onto the foot piece.

Drawing File

Part 2: Servo Band

Fig. 4 Servo Band

There is a total of four “Servo Bands” located on the Micro FOBO. This part is responsible for grouping two micro servos together which forms a section of a leg. The two servos are pressure fitted into the square cutout and thus this part must be dimensionally precise to prevent servos to come loose. This piece had several revisions to satisfy the dimensional accuracy need to keep the servos secure. The servos were measured with a caliper and the thickness of the servos stickers even had to be considered when designing this piece. Due to leg movement constraints, only one servo can have extra material to be screwed onto the part.

Drawing File

Part 3: Servo Bracket

Fig.5 Servo Bracket

The ‘Servo Bracket” is a shorter version of part 0: servo hip and serves a similar purpose. This component mounts onto two servos that are located on the servo bands. This allows the second to the top servo to move the lower leg. This piece is located in the middle of the leg and connects the top and lower sections. This piece can be thought as the knee of the robot. Just like the other brackets, there are two cutout trenches that allow servo horns to be mounted and secured through a single screw. This piece can be varied in length to adjust the height of the robot and adjust the walking stride of the robot itself.

Drawing File

Part 4: Servo Wrap

Fig.6 Servo Wrap

The “Servo Wrap” is a small piece that attaches the back of the hip servo (top leg servo) to be mounted onto part 5: Bearing Frame. It is connected via an M2 screw that is 18mm in length. The screw goes through the servo, through the servo band, and screws into this piece. A hole on the left side of the wall was added to allow the servo wires to feed through and connect back to the electronics. Notice there is a hexagon trench located near the middle of the part. This trench allows an M3 nut to be placed in that location and lets a screw to secure Part 4 with Part 5. Another key design feature is the chamfer cutout located on the backside of the part. This permits higher degrees of movement from the hip servos by at least 45 degrees more.

Drawing File

Part 5: Bearing Frame

Fig.7 Bearing Frame

The “Bearing Frame” is a mirror-like component to part 0 as both pieces work together to provide the connection of legs to body. One of the key differences is that this piece contains two large circular trenches in which a bearing can fit onto. Using a 10mm circular bearing we place it on the part to provide free angular movement to the left and right sides of the pieces. Once the bearings are fitted inside, we can use M3X14 bolts to attach the servo wrap pieces to the left and right side of the Bearing Frame. Since the legs servos are already attached to the servo wrap we effectively attached the two legs to the body of the robot.

Drawing File

Part 6: Body Riser

Fig.8 Body Riser

Micro FOBO mainly consists of a head and two legs but this part, body riser, can be considered the body of the robot. This component connects the two attached legs with the head. There are two fork-like structures located at the top of the piece that allows part 0 and part 5 to fit in snugly effectively connecting the two legs to this piece. Part 0 and part 6 are secured through a couple of M3 screws with an approximate length of 16 mm. The back side of this component is flat and has two holes for connecting to part 7 which is the electronics frame. The body riser can be increased in height allowing the robot’s head to be located higher above the legs. We can experiment with changing the height to allow shifting the robot’s center of mass higher or lower as needed.

Drawing File

Part 7: Electronics Frame

Fig.9 Electronics Frame

The Electronics Frame is a thin component that is responsible for connecting the PCB to the body riser. The PCB will contain four mounting holes which will allow the board to connect to this part. Note that the part contains extruded cubes that correspond to the location of the PCB hole mounts. These extruded cubes also have a hole cut out to fit M3 screws that secure the board in place. Finally, the part can be secured to the head via similar M3 screws on the side of the part and head

Drawing File

Part 8: Head

Fig.10 Head

One of the first challenges in creating a miniature FOBO we observed was that our robot would need to support large amounts of electronic components that used to be on the regular size FOBO. These electronics would need to be smaller in size or our head design would need to optimize to fit all the electronics. Our first design was based on the prediction that the new electronics would have a smaller footprint and thus the head of the Micro FOBO is much smaller. The exact dimensions can be found on the link below. Once the size of the head was set I began to look at some redesigns that I can implement to change the look and functionality of the robot’s head. That is when I stumbled on an image of a tin toy robot from the 1950s.

Fig.11 1950’s Tin Toy

As you can see from the image above this robot has a similar head as the FOBO which gave me the idea of emulating the design of the face. The ultrasonic sensor will take place as the robot’s eyes and the mouth and nose features would simply be aesthetics. Another thing that I noticed was that the tin toy contained antennas on the left and right side of the head. One of the redesigns I wanted to incorporate since the beginning was adding turn signals to the robot and the antennas can certainly be used for that. My idea is to have small 5mm red LED’s as the tip of the antennas that would blink indicating when the robot will turn and in what direction. Finally, we see that there is a small red light on top of the robot that can be designed to indicate on/off status of the robot.

Fig.12 Mechanical Design Improvements

Drawing File        Tin Robot Toy

 

Spring 2018 3DoT Hexy: System Block Diagram

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By: Raymundo Lopez-Santiago (Mission System and Test)

Verified by: Eduardo De La Cruz (Project Manager and Manufacturing Engineer)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction

This blog post covers 3DoT Hexy’s System Block Diagram. The 3DoT Hexy robot along with all its peripherals will be powered from a single 3.6V RCR123A battery. The 3DoT board will connect to all other devices. The 3DoT board comes equipped with a BLE Bluetooth module, Dual DC motor driver and (3) 8-pin connections to attach peripherals. Communication for mobile operation of 3DoT Hexy will be done using a BLE Bluetooth module which will be paired to the ArxRobot application. Two separate custom PCBs will be designed and sent for fabrication. The custom sensor PCB will have an I2C expander which will incorporate all sensors which include the color, ultrasonic, and light sensor. The custom Boost Converter PCB to provide 5V to the micro metal motors used to drive the gears/cam-system as well as three UV LEDs. Fig. 1 shows the system block diagram for 3DoT Hexy.

Update 04/17/18

Due to changes in the maze printing material and the fact that we are no longer using a boost converter, the UV LEDs will no longer be used and instead IR LEDs along with Light sensors will be used to handle intersection detection. Another change that is noticeable is instead of using an 8-channel I2C expander, we are now using a 4-channel I2C expander. The color sensor was removed from the design since we are using light sensors for intersection detection. A new addition to the design is the use of a gyroscope to aid in directional turning and two LEDs to act as eyes of the spider robot. The interface matrix was updated to reflect changes. Fig. 2 shows the updated system block diagram for 3DoT Hexy. Only 8-pins from the bottom shield of the 3DoT board will be used.

Fig. 1: 3DoT Hexy Updated System Block Diagram

 

 

Preliminary System Block Diagram (03/15/18)

The system block diagram mimics the interface matrix developed for 3DoT Hexy. The 3DoT Hexy system block diagram below shows the different parts of the robot and how they interact with each other. A total of 9 pins out of the 16 pins available from the 3DoT board will be used for the custom PCB’s. The two custom PCB’s will be designed and built to add an I2C expander which will connect to all sensors, also a boost converter to provide 5V to the motor driver. 3DoT Hexy will be powered from a single 3.6V RCR123A battery. Communication for mobile operation of 3DoT Hexy will be done using the HM-11 bluetooth module. Any changes will be added as needed.

 

Fig. 2: 3DoT Hexy System Block Diagram

 

Conclusion

The system block diagram is designed taking in consideration of the 3DoT board as the main board to control any attached devices. Visually the system block diagram helps identify connections between devices and how many pins will be allocated or needed. The interface matrix and system block diagram were developed around the same time. I highly recommend to pair these two tasks very close to each other.

References

  1. https://www.arxterra.com/2016-spring-3dot-david-final-project-blog-post/
  2. https://www.arxterra.com/spring-2018-3dot-hexy-interface-matrix/

Spring 2018 3DoT Hexy: Product Breakdown Schedule

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By: Raymundo Lopez-Santiago (Mission, System and Test)

Verified by: Eduardo De La Cruz (Project Manager and Manufacturing Engineer)

Approved by: Miguel Garcia (Quality Assurance)

Introduction

This blog post covers the Product Breakdown Schedule (PBS) for 3DoT Hexy. This document follows the Work Breakdown Schedule (WBS) developed by Eduardo De La Cruz (Project Manager and Manufacturing Engineer). This PBS is split into five sections to outline the major components of 3DoT Hexy. The five sections are electronic hardware, software, movement, manufacturing, and power. Anything for movement which includes motors, joints, gears, and legs are the main parts in for mobility of the robot. Under the software section, communication via Bluetooth from a smartphone and the Arxterra app will allow for wireless control of 3DoT Hexy with custom commands. For electronic hardware, all peripheral sensors will be connected to a custom PCB.  Sensors used for this project include three UV light sensors which will aid in detecting intersections, an ultrasonic sensor which will aid in detecting other robots, and a gyroscope to aid in directional turning. For manufacturing, it includes designing a cam system. chassis, legs, joints and any other parts used for the mechanism. It also includes rendering models on Solidworks and 3D printing parts in either PLA/ABS plastic or other approved material. For the power section, 3DoT Hexy and its peripherals will be powered by a single 3.6V RCR123A battery. Power estimates of each components are further listed in the resource reports blog post.

Fig. 1: 3DoT Hexy Product Breakdown Structure

 

Conclusion

After going through two revisions after the PDR, I made sure this PBS was effective in following the WBS. For future reference, make sure to only define major components for the robot and not specific details. Do not try to go to a different path than the WBS, since the overall objective is to identify major components and who is responsible for them to further help with the production of the final product.

References

  1. https://www.arxterra.com/2016-spring-3dot-david-final-project-blog-post/
  2. https://docs.google.com/document/d/18vVkXfxwqulRn5qCdm2Y6NYleS1iGQ_p3y6FJUj5NJ4/edit

 

Spring 2018 3DoT Hexy: Interface Matrix

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By: Raymundo Lopez-Santiago (Mission, Systems, and Test)

Verified by: Eduardo De La Cruz (Project Manager and Manufacturing Engineer)

Approved by: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction

This blog post covers 3DoT Hexy’s final interface matrix. If interested in seeing our preliminary design interface matrix click here. The 3DoT Hexy interface matrix was developed with information obtained from datasheets for each device used and pins allocated from the 3DoT V 6.43a board. Based on our design, we needed to design two custom PCBs, one for all sensors and one with a boost converter to drive our motors as well as power three UV LEDs. To make things easy to understand, the interface matrix is broken up into three interface matrices. As seen in Fig. 1, the main interface matrix relates each custom PCB to the 3DoT board and how each PCB will connect to the 3DoT board. As seen in Fig. 2, the Custom Sensor PCB interface matric further breaks down in detail which sensors will connect to the PCB to make sure no pins are used more than once (except for power and ground). As seen in Fig. 3, the Custom Boost Converter PCB also breaks down in detail which peripherals will connect to the PCB to make sure no pins are used more than once (except for power and ground). After researching different UV sensors, we were unable to find ones that had different I2C addresses, therefore we needed to add an I2C expander to our circuit design. Based on availability and previous semester success, the model I2C expander model used is TCA9548A. The boost converter model used is TPS61253A.  The Light Sensor (UV Index Sensor) model used is Si1145. The gyroscope model used is ITG-3200. The Ultrasonic sensor model used is Parallax Ping (a HC-SR04 may also be used).

Related Requirements

Level 1 Requirements

L1-4:

The robot shall have a custom PCB as platform to build from and will incorporate peripherals for sensors

C-12:

The robot shall use a v6.43a 3DoT board.

Level 2 Requirements

L2-2:

The robot shall use a single RCR123A 3.7 V, 650mA rechargeable Li-ion battery to power the 3DoT board, which will power the drivetrain and all attached peripherals.

L2-3:

The robot shall use three Light sensors and three IR LEDs connected to a custom sensor PCB to handle intersection detection.

L2-4:

The robot shall use a Parallax Ping (or HC-SR04) ultrasonic sensor to handle robot avoidance.

L2-10:

The robot shall have (2) LEDs acting as eyes of the spider.

 

Update 04/24/18

Based on customer concerns with the TPS61253A 9-ball 1.2-mm x 1.3-mm WCSP package, we explored other methods to not use a boost converter and further investigate operating all electronics of the robot at the rated 3.7 V from the RCR123A battery. After improving the gear mechanism with the addition of bearings and bushings, we were able to operate the robot at 3.7V while having stable movement with weight attached on top of the robot (simulating the final weight of all devices used for the final robot configuration). Since this change occurred, we no longer will use any connections from J1 and J2 from the 3DoT board. UV LEDs will no longer be used and will be replaced with IR LEDs. Based on customer recommendation instead of using the 8-channel TCA9548A I2C model, we are going to use a 4-channel model: PCA9544A. All peripheral devices will be connected to the Custom Sensor PCB developed by Kris Osuna (Electronics and Control Engineer). The Custom Sensor PCB is connected to J3 of the 3DoT board.  Two additional extra LEDs are added to act as eyes of the spider.

 

Fig. 1: 3DoT Hexy Interface Matrix

Fig. 2: Custom Sensor PCB Interface Matrix

Fig. 3: Custom Boost Converter PCB Interface Matrix

Conclusion

This blog post covers 3DoT Hexy’s interface matrix. This matrix is composed of the available pins of the 3DoT V 6.43a board and how they connect to each custom PCB. When using the Custom Boost PCB conected to the 3DoT board, Make sure to remove JP7 on the 3DoT board. This will avoid you messing up the 3DoT board. The objective of this document is to allocate pins to components used in the design and make sure no pin is used twice (except power and ground).

References

  1. https://www.arxterra.com/2016-spring-3dot-david-final-project-blog-post/
  2. http://www.ti.com/lit/ds/symlink/tps61253a.pdf
  3. http://www.ti.com/lit/ds/symlink/pca9544a.pdf
  4. https://cdn-shop.adafruit.com/datasheets/Si1145-46-47.pdf
  5. https://www.sparkfun.com/datasheets/Sensors/Gyro/PS-ITG-3200-00-01.4.pdf
  6. https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf

Spring 2018 AT-ST Shaft Encoder

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By: Joseph Cho (Mission, Systems, and Testing)

Verified By: Initiser Kabir (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction

For our AT-ST project, the two motors on the legs have to be precise. In order to know the exact location of the turns, shaft encoders have to be added. The shaft encoders that have been chosen will be using a magnetic shaft encoder. The magnetic shaft encoder uses hall effect to determine the rotation of the axle.

Hall Effect

The shaft encoder is packaged with a 6 pole magnetic disk that is used to provide the magnetic field. Hall effect is observed when magnetic field causes the small current of elections to deviate and produce Hall voltage. When the magnetic disk rotates, it causes changes in magnetic fields. The hall effect latch (TLE4946-2K) inside the shaft encoder will sense these changes and output values. Using these output values, the position of the axle will be determined.

 

Connections on shaft encoder

Figure 1: Connections on shaft encoder

Description:

The shaft encoder has 6 pins. The M1 and M2 pins on the right are for powering the motor. The motor will be connected directly to the shaft encoder by soldering M1 and M2 holes in the center of the board. GND and VCC are used for powering the board. Output A and Output B are the outputs from the two TLE4946-2K hall effect latches.

After contacting the previous blog post author, the decision to use only one of the output has been made. The shaft encoder has two hall effect latches for accuracy and using only one of them is sufficient enough for our uses. A trade-off study may be done to test the amount of current used and the accuracy of the shaft encoder.

GearMotor with Shaft Encoder

Figure 2: GearMotor with Shaft Encoder

The image above shows that the shaft encoder is soldered onto the motor directly with male headers.

Schematic of Shaft Encoder

Figure 3: Schematic of Shaft Encoder

Description

The schematic shows the connections of the shaft encoder. The motor will be soldered onto M1 and M2 which will be powered by pin 1 and pin 2 of the shaft encoder. Pin 3 and pin 4 are used for Vcc and Ground. Pin 4 and pin 5 are outputs of the shaft encoder hall effect readings.

Reference

  1. https://www.pololu.com/product/3081/specs
  2. https://www.pololu.com/file/0J814/magnetic-encoder-kit-for-micro-metal-gearmotors-schematic.pdf
  3. https://www.pololu.com/file/0J815/TLE4946-2K.pdf
  4. https://www.arxterra.com/motor-shaft-encoder-trade-off-study/
  5. https://www.electronics-tutorials.ws/electromagnetism/hall-effect.html
  6. https://www.pololu.com/product/3081/specs#lightbox-picture0J6835;main-pictures

Goliath Spring 2018 – Work Breakdown Structure

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By: Ernie Trujillo (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Figure 1 – Diagram for the Work Breakdown Structure of the Goliath Team members.

The Work Breakdown Structure (WBS) provides organization for the tasks a team is required to complete for a project. For the Goliath team, the WBS offers a general overview of the objectives that every team member is required to do. The tasks are broken down in terms of the type of engineer (MST, E&C, and M&D), and then within each field, it goes into further detail as to what each position’s tasks entail. This diagram offers each engineer a quick overview of the responsibilities that their position takes on.

 

Goliath Spring 2018 – Product Breakdown Structure

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By: Ryan Nguyen (MST Engineer)

Verified By: Ernie Trujillo (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Figure 1 – Diagram of the Product Breakdown Structure.

Like the Work Breakdown Schedule, the product breakdown schedule breaks down the products and the personnel responsible for them. In the spring 2018 project, the Goliath is broken into three products: Electronics, Program and Control, and Manufacturing. All components such as shields and sensors are the responsibility of Milton, as they go on the custom PCB. Tai creates the programs for movement and ultimately completing the mission. Ryan takes care of the communication between the mobile App, control panel, and robot. Lastly, Daniel fabricates the Goliath.

Goliath Spring 2018 – Preliminary Resource Report

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By: Ryan Nguyen (MST Engineer)

Verified By: Ernie Trujillo (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Figure 1 – Spreadsheet for expected expenditures for the Goliath Tank.

The cost report was based on the previous projects, with large uncertainty placed on 3D printing as it is undetermined how many iterations will be printed. Several items are free as they are provided by the class, others are taken from online. The shipping price is considered an uncertainty. Project allocation of $200 dollars was given by the mission objective to make a relatively cheap toy.

Figure 2 – Spreadsheet for the mass of the components.

Much of the mass report are assumptions, based on visual inspection of parts online. Many parts do not list the mass, such as sensors. It is decided to put 10% margins on all parts as they could fluctuate once the product solidified. Project allocation was based on a requirement that the Goliath shall withstand all impact with all robots; thus the chassis must be quite sturdy.

Figure 3 – Spreadsheet for the power consumption of the components.

The power report needs more information in measuring the power draw, this will be done once some sort of system is established for parts such as the 3Dot board and motors. Sensors’ measurements are from data sheets that manufacturer provide. Project allocation comes from the maximum instantaneous current the RCR123A can provide.

Goliath Spring 2018 – Preliminary 3D Model

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By: Daniel Guerrero (M&D Engineer)

Verified By: Ernie Trujillo (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Figure 1 – Preliminary design for the center console of the Goliath.

The latest design created came out as one piece to print, but as I add walls and other portions of the tank, that will change. I’ll begin by dividing the tank into 4 sections; the 2 side walls, the center bottom portion, and the center top portion. When creating the next design I’ll also be adding the side box features and possibly use them as storage or placement for sensors or other electrical components implanted into our project.

For the upcoming designs I’m planning to stay close to the overall shape of this design but accommodate for the equipment being placed inside and adding the side features to the original 302 goliath tank between the treads. I’ll also aim to get closer and closer to the 1/16 scale model of the actual tank. Currently, I am also researching design concepts to creating a closing feature to the center console of the tank that will have a hinge at one end and allow the top hatch to open and close completely.

Spring 2018 AT-ST System Block Diagram

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By: Joseph Cho (Mission, Systems, and Testing)

Verified By: Initiser Kabir (Project Manager)

Approved By: Miguel Garcia (Quality Assurance)

Table of Contents

Introduction

The system block diagram is made to visually show the systems of our product, AT-ST. The 3DoT board is the center of the system consisting the microprocessor and motor headers. There will be custom PCB that are connected to the 3DoT board for telemetry and sensors.

System Block Diagram

Figure 1: System Block Diagram

 

Description

The System block diagram above for AT-ST help visualize the system of the AT-ST.  The 3DoT board uses ATmega32U4 as the microcontroller. The 3DoT board consists of microcontroller, bluetooth transceiver,  servo header and dual motor driver. The 3DoT board (v6) will also be connected to the servos, motors and main custom PCB. PCB1 will be the master PCB that routes all input and output for the sensors. PCB 2 and PCB 3 are used for UV sensors which will be connected to the I2C expander on PCB 1. Bluetooth transceiver will connect to a mobile device using the Arxterra app via bluetooth.

I2C Expander

The UV sensors has to be connected to the I2C expander because the I2C address of same sensors will be overlapping. If we were to use a metaphor of I2C addresses, they are different phone numbers that are used to communicate. If two people were to have the same phone number, there would be a major problem. Signals may be overlapped, misguided, and destroyed when the addresses overlap each other.  The I2C address of the Si1145 (UV sensor) is set on 0x60, so I2C expander has to be used to change the single address into two different addresses. One thing to be cautious about is that the new address should not overlap the address of gyroscope (0x68 or 0x69).

 

References

  1. https://www.arxterra.com/fall-2017-velociraptor-preliminary-design-document/
  2. https://learn.adafruit.com/i2c-addresses/the-list