Written by Zachary de Bruyn (Electronics & Control)

Purpose

The PeteBot chassis team is unique in that it is utilizing two PCBs which operate on two different MCUs; the first being the heritage 3DoT v5.03 board which uses the ATMega32U4, and the second being the SAMB11, which incorporates the ATSAMB11. One significant different between the two boards is that the SAMB11 has a transceiver module. Because the SAMB11 can operate with the incorporated Bluetooth (BLE), an antenna network was needed to be designed to utilize the BLE transceiver. Because an antenna network was needed to be constructed with minimal input from the SAMB11 reference design, many steps were required to be performed in order to ensure that the SAMB11 could operate at the 2.4-GHz BLE frequency.

Antenna Selection

The first step in the overal process of incorporated a matching network is selecting a proper antenna based on the needs of the system. To reiterate, the operating frequency of BLE is 2.4-GHz. Along with frequency requirements, there are also size requirements. Our antenna therefore was required to operate at the BLE frequency, to be small enough to fit on a PCB, and to operate the PeteBot chassis. These requirements alone narrowed the possibilites of two types of antennas: PCB or chip antennas. With the PCB antennas, one antenna that looks promising is the meandered inverted-F antenna (MIFA). The chip antenna resembles a 0805 resistor or inductor. The two antennas are shown below:

Analyzing both types and data sheets of antennas, we discover that both antennas have an isotropic radiation pattern, meaning that the frequency of the antenna can be picked up equally from almost every direction. This is ideal for our applications due to the fact that the PeteBot will be required to operate via RC mode by an operated. A few other important antenna parameters are: return loss, gain, and bandwidth. Return loss is essentially how much of the power being transmitted is reflected due to the mismatch of the antenna’s imepdances. The standard for impedances is usually 50-Ohms. A return loss greater or equal to 10-dB is considered ideal for operation [1]. Referring to the following equaltion for return loss:

At a return loss of 10-dB which translates to 90% of power transmittered going into the antenna, return loss of 20-dB translates to 99%. The gain is a measure of ow strong the radiation field is compared to the ideal omnidirectional antenna. For isotropic antennas, like that being applied to the PeteBot, gain is measured as dBi. The “i” simply indicates that the gain is measured frerence to an istropic antenna. While the MIFA antenna has a gain of about 5-dB depending on the plane of radation, the chip antenna has a peak gain of 0.5-dBi. The bandwidth requirements for the antennas requires that the BLE frequency is capable of interception, which was 2.4-GHz. The chip antenna has a frequency range of 2.4- to 2.5-GHz, which translates to a bandwidth of 100-MHz. The MIFA antenna operates a a comparable frequency range, and therefore has an equivalent bandwidth.

With comparable operational characteristics, an antenna selection for our purposes was based upon flexibility, in which the antenna can be used in a variety of configurations for the SAMB11 board. In the case of the PeteBot SAMB11 PCB, the chip antenna is the best candidate.

Matching Network

The purpose of an antenna matching network is to allow the most power to be delivered to the load. The load in the case of transcievers, like the SAMB11, is dependent on whether the antenna is transmitting or receiving. If the antenna is transmitting, then the antenna is the load, whicl the SoC SAMB11 is the load if the system is receiving. It is common practice to design a load with 50-Ohm impedences for RF traces [1]. As a review, the term impedance is mathematically defined as the magnitude of resistance and reactance. It is typically denoted by the letter “Z.”

In Equations (2) and (3), R denotes resistance, and X for reactance. Both values are measured in Ohms.

Now that impedance is defined and the typical characteristic impedance is defined as 50-Ohms, this information can be used in collaboration with the helpful tool called a Smith Chart.

Smith Chart

It is a graphicaly tool used to help plot complex impedances and used to define a matching network. It is also helpful in determining many important RF parameters, including VSWR, return loss, reflection coefficient, and transmission coefficients. Using this chart can design a matching network.

There are a lot of reference towards using Smith charts on YouTube that will explain how to find the difference parameters.

The best usage of the Smith chart is to be able to measure the input impedances going into a load, where the input impedance is defined as Z_in. Character impedance is Z_0 and the load impedance is Z_L.

As an example, let’s say that the measured Z_in was 100-j100-Ohms. The first step would be to normalize the input impedance by dividing Z_in by Z_0, which would result in 2-j2-Ohms. This opint can be located on the Smith chart, and from this point (2-j2), you can use a combination of inductors and capacitors to move the impedance to the necessary location on the Smith chart, which is the center of the chart where the red dot is in Figure 3. The table below helps better understand how each component affects the impedance of the matching network.

Using any combination of passive elements can be used to get measured impedance as close as possible to the center of the Smith chart for optimal performance. If we refer to the matching newtorks in Figure 4 and Figure 5, we can see that the matching network consists of the passive elements described in Table One.

Figure Five depicts the matching network reference design for the SAMB11 where the resistance network shown in the dotted square is omitted from the final design PCB. Also omitted was the capacitor laveld DNI (Do Not Include).

S-Parameters

Scattering parameters, or “S-parameters” are a set of parameters which define the electrical power delivered between two ports on a network, where a port is any where within the network containing voltage or current delivery [6]. The four parameters are displayed below:

The reflection coefficient referred to in the S11 description is defined as followed:

Where  are the reflected and incident plane waves, and the  is the intrinsic impedance of the medium the wave is traveling through, and  is the intrinsic impedance of the surface/material medium the wave reflects or penetrates [5].

The S-parameters can be collected by using a Vector Network Analyzer, however they are fairly expensive, usually greater than $10,000 on the lower end models. As a substitute, there is software such as Microwave Office or Optenni which can calculate the S-parameters as well. While these software suites are NOT free, they do offer free “research” trials where you can use it free for a week (Microwave Office) or for a month (Optenni).

Optenni provides the most tutorials on how to get familiar with the basics of the software, and also offers an optimization tool which allows you to designate specific requirements you want for your design. For instance, in the case of the SAMB11 3DoTX board, the requirements for BLE is that it resonate at 2.4-GHz. By using Optenni, desired parameters can be chosen, and a matching circuit will be automatically constructed through the software. (Click Here, it will redirect you to the Optenni technical resource page).

Example

As seen in the S parameter chart in figure 6, the S11 parameter extends just beyond -20-dB. The figure therefore suggests that at approximately -20-dB the antenna radiates at its maximum. At 0-dB the antenna radiates nothing. While this simulation may  look ideal, it is not practical for real world application. This is because the dark blue highlighted bandwidth (2.4-2.483-GHz) is difficult to realize in the physical world. In practical antenna circuits, the resonating frequency an antenna could transmit/receive is always met with some percentage of error, or acceptable deviation from nominal conditions. For example, the chip antenna we have chosen for the 3DoTX board has a frequency range from 2.4 to 2.5-GHz. A 100-MHz difference. By choosing more than the two components that have been shown below, more components can be added to open up the bandwidth of frequencies that can be received/transmitted by the antenna. Another great feature with Optenni is that you can tune the component values to see how each one effects the S11 parameter.

By looking at the smith chart in figure 7, we see that dark blue are highlighted on the graph corresponds with the dark blue area highlighted in figure 6. Recalling the information presented earlier about the smith chart and 50-Ohm impedances, we can see that the matching circuit accurately tunes the antenna to operate at the matched approximate 50-Ohm impedance.

In the matching circuit shown, the port corresponds with the input (i.e. the antenna) and the load corresponds with the SAMB11.

References

[1] Reference One

[2] Reference Two

[3] Reference Three

[4] Reference Four

[5] Fundamentals of Engineering Electromagnetics by David Cheng

[6] Reference Six

Acknowledgements

Thank you for Dr. Densmore, Dr. Rezvani, and Dr. Haggerty for help in contributing to understanding the matching network.

(Written by Elizabeth Nguyen (Project Manager) & Melwin Pakpahan (Missions, Systems, & Test)

Objective

The requirements for the PeteBot (3DoT Chassis) are defined at two levels and provide the team with direction and to determine what shall be accomplished. Verification and validation are also outlined.

Current Status:

At this time, not all requirements have been confirmed and are pending approval. Some of the requirements listed below are different from the requirements listed in the PDD.

Level One Requirements

Program Requirements

1. PeteBot shall be completed by Wednesday, December 13, 2017.
   1. This requirement coincides with the last day of class.
   2. This is the projected demonstration date for all toy robots.
2. PeteBot shall cost no more than $200 as projected by the customer.
3. PeteBot will be a toy robot.
   1. This requirement is defined through the customer expectations.

Project Requirements

1. PeteBot shall use the PBX11 which is an alternative microcontroller to the 3DoT Board that utilizes the SAMB11 chip instead of the ATMega32U4 chip.
   1. In case the PBX11 board is inoperable, the 3DoT Board shall be used in its place.
2. PeteBot shall navigate through a maze with remote control through the ArxRobot App or the Arxterra Control (based on Project and Mission Objectives).
3. PeteBot shall be no larger than 4 x 3.5 x 3 inches.
   1. These measurements were taken at the widest dimensions of the chassis since it tapers at the bottom.
4. PeteBot shall be able to memorize a path through the maze that is taught by the user (based on Project and Mission Objectives).
5. PeteBot shall be able to autonomously travel down the path that was memorized (based on Project and Mission Objectives).
6. PeteBot should be able to navigate the maze and avoid collisions when multiple robots are in the maze.
   1. The Rules of the Maze for the avoidance algorithm have been defined.
   2. Line following will be implemented if the motoer encoders are funtional.
7. PeteBot shall have a chassis that is 3D printed.
   1. This is derived from a customer expectation.
8. The total 3D print time of PeteBot’s chassis shall not exceed 2 hours (based on Project and Mission Objectives).
9. The main body (chassis) of PeteBot shall be of one solid piece.
10. PeteBot shall be assembled per the guidelines of Disassembly and Reassembly.
11. The PeteBot Paper Shell shall resemble the CSULB mascot, Prospector Pete.
    1. This is a customer expectation.
12. The PeteBot shall be able to perform all functions as programmed by the Arxterra app.
    1. This includes custom commands.

Level Two Requirements

System Requirements

1. PeteBot shall operate for no less than 20 minutes using a fully charged battery.
2. PeteBot shall attain an operating speed no slower than 3 centimeters per second.
   1. This speed is referenced from Mission Duration.
3. PeteBot shall utilize the Generic Color Sensor Shield for line-following.
4. The PBX11 board shall fulfill the requirement to be a custom PCB.

Subsystem Requirements

1. PeteBot shall be powered by a RCR123A Lithium Polymer battery.
2. PeteBot shall use a planetary gear system.
3. The Generic Color Sensor Shield shall be located at the front of the PeteBot.
4. PeteBot shall have a castor wheel under the Generic Color Sensor Shield to support the mobile phone.
5. PeteBot shall utilize two GM6 brushed DC motors with an extended D-shaped shaft.
6. PeteBot shall utilize two shaft encoders for line following.

Written by Zachary de Bruyn

Purpose

The purpose of this experiment was to test the TCS34725 RBG Color-to-Digital sensor to determine if it was applicable for the purposes of the EE400D project “PeteBot”. The testing included testing of the sensitivity of the sensor, its ability to distinguish difference between colors, and performing studies as to the limitation of the sensor.

DC Characteristics of the TCS

The TCS operates at a nominal voltage of 3-V with a maximum being 3.6-V. Depending on the state of the device, the current drawn ranges from 235-uA in an active state down to 2.5-uA in a sleep state.

DC Characteristics at the board level

The board is designed for usage with the Arduino where the VIN input is designed for 5-V, and draws XXXX A current.

The TCS34725: The TCS34725 at the component level is the physical IC located on the breakout board that reads colors and digitizes them for the benefits of the user. Therefore when referring to the TCS34725, it is in reference to the actual IC, whereas when referring to the board, it is implied that we are talking about the entire board with all IC’s and passive components.

The TCS utilizes an I2C interface with a slave address as 0x29 in hexadecimal. Therefore in order to implement multiple TCS’ within the same I2C bus, certain precautions will need to be utilized, such as an I2C extender.

The block diagram of the TCS is shown below. From the diagram it can be seen that the light entering the sensor is filtered before going through four ADC afterwhich the signal is digitized into four different color data sections: Clear, Red, Blue, Green. The digitized data is then sent via I2C bus to the respective MCU being utilized; in this case the Arduino Uno.

Breakout Board: The schematic of the breakout board is provided below, and is courtesy of Adafruit.

As shown by the breakout board schematic, the board is powered by a 5-V input through the VIN pin on the board, and is then stepped down through an LDO (RT9193) to 3.3-V. The 5-V is also used for the source voltage for the two MOSFETs utilized in the circuit. The 3.3-V is then used as the gate voltage for the MOSFETs, and is also the input voltage necessary for the majority of the circuit including the TCS and LED MOSFET.  The breakout board also utilizes this 3.3-V and provides a 3.3-V output through the board (via pin 3, ‘+3V3’).

Test Set-Up

The purpose of this test was to determine the TCS’ ability to distinguish between colors. This test was performed by covering a square piece of cardboard with white tape, and then applying a half-inch strip of electrical tape down the center. The black tape is to simulate the lines of the maze, and the TCS’s ability to detect between colors. The basic test setup is given by Adafruit, where the VIN pin of the breakout board is powered via the 5-V of the Arduino, and the SDA and SCL inputs are connected to analog pins 4 and 5.

Next a circular wall was constructed to surround the breakout board so that testing can be done in a controlled environment which would mitigate the sensors ability to pick up any ambient light. This wall also allows us to maintain a static distance between the breakout board and the test strip that will be utilized to test the sensors ability to distinguish colors. Two LED’s were also utilized which would help determine if the correct value was being measured. When the correct color was measured (predetermined by me) the green LED would emit, else the red LED would light.

The code below was provided in the Adafruit library, and was modified in order to test the ability of the board to read colors.

/* Source provided by Adafruit and modified by Zach de Bruyn CSULB EE400D
   Connect SCL    to analog 5
   Connect SDA    to analog 4
   Connect VDD    to 5V DC
   Connect GROUND to common ground
 */

#include <Wire.h>
#include "Adafruit_TCS34725.h"

const int greenLED = 4;
const int redLED = 7;
const int fwd = 10;
const int rvs = 11;

/* Initialise with specific int time and gain values */
Adafruit_TCS34725 tcs = Adafruit_TCS34725(TCS34725_INTEGRATIONTIME_700MS, TCS34725_GAIN_1X);

void setup(void) {
  Serial.begin(9600);
  pinMode(greenLED, OUTPUT);
  pinMode(redLED, OUTPUT);

  if (tcs.begin()) {
    Serial.println("Found sensor");
  } else {
    Serial.println("No TCS34725 found ... check your connections");
    while (1);
  }

}

void loop(void) {
  readSensor();

 }

void readSensor (){
    uint16_t r, g, b, c, colorTemp, lux;

  tcs.getRawData(&r, &g, &b, &c);
  colorTemp = tcs.calculateColorTemperature(r, g, b);
  lux = tcs.calculateLux(r, g, b);

  Serial.print("Color Temp: "); Serial.print(colorTemp, DEC); Serial.print(" K - ");
  Serial.print("Lux: "); Serial.print(lux, DEC); Serial.print(" - ");
  Serial.print("R: "); Serial.print(r, DEC); Serial.print(" ");
  Serial.print("G: "); Serial.print(g, DEC); Serial.print(" ");
  Serial.print("B: "); Serial.print(b, DEC); Serial.print(" ");
  Serial.print("C: "); Serial.print(c, DEC); Serial.print(" ");
  Serial.println(" ");

 // digitalWrite(greenLED, HIGH);
  int color = r + g + b;

  Serial.print("Color: "); Serial.print(color); Serial.print(" ");

  // If black is sensed turn green LED on, else red LED is on.
  if (color < 8000 && color > 7000){
    digitalWrite(greenLED, HIGH);
    digitalWrite(redLED, LOW);
  }

  else{
    digitalWrite(redLED, HIGH);
    digitalWrite(greenLED, LOW);
  }

}

As seen in the redSensor() function. It is within this function that the sensor reads the individual digitized color. A variable ‘color’ was created which summed these values, and then these values were compared to a predefined range which would measure the black strip on the white background. In this case, the range was from 7000 to 8000.

Test Results

Video: Color Sensor Demonstration

Written by Melwin Pakpahan (Mission, System, Test)

Description:

The power consumption of the 3DoT board will be measured as follows. A RCR123A battery will be connected in series with a test resistor and the 3DoT board. Two versions of the 3DoT board will be tested and compared. The test resistor is chosen to be 1 ohm, and the current draw is to be determined. When the power source is switched on, the voltage across the resistor is used to calculate the current going through the circuit using Ohm’s law.

 

Considerations

• The battery is fully charged before any test is conducted.
• A test code (“Motor_Operation_Test”) has been verified and uploaded to the 3DoT Board.
• The motors continulously run during the test.

Cases

There are three cases of testing for the power consumption.

1. Case One – Testing power consumption with no motors
2. Case Two – Testing power consumption with one motor running
3. Case Three – Testing power consumption with two motors running

Case One

Figure One  shows the circuit diagram for this first test:

Case Two

A GM6 motor is connected and running as shown in Figure Two.

Case Three

Two GM6 motors are connected and running as shown in Figure Three.

Constraint

Up until this point, Bluetooth communication has not been established yet. The procedures above will be repeated once communication is established.

Results

Figure Four shows a measurement of the resistor. Although, the specified value is 1 ohm, the actual value is 1.1 ohm. This measured value is desired since it provides a more accurate measurement of the current values. Figure Five shows the test run of the 3DoT board Rev 4.46 without actuators and without Bluetooth pairing. Table 1 shows the results of each test case.

Table of Results

References:

[1] Featured Image

Written by Elizabeth Nguyen (Project Manager)

Description:

A short list of custom commands and custom telemetry are defined in preparation for the EE 400D Fall 2017 Mission.

Custom Commands

• Adjustable Speed Commands – Allows the robot to run at a specific set speed
  • Option for slowest speed
  • Option for medium speed
  • Option for fastest speed
  • On/Off for adjustable speed
• Emergency On/Off Command – in the case that the robot is incapable of operating in Phase 2b
  • This is to avoid damage to the robot and other robots
  • Avoids the need for anyone to step into the maze and pick up the robot to disable it

Custom Telemetry

• Display of Phase the robot is operating in
• Robot detected
  • State that the robot is in during robot avoidance