Category: E&C – MCU Subsystem Command Programming

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When there is an error in a command sent to the Arduino/3DoT, a telemetry packet with an Exception Code will be returned. Below is a list of the possible Command Exception codes. Following that, an example showing how to read exception code telemetry is provided.
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The finite state machine for command processing and decoding will generate the exception or error codes listed below. These codes will be sent to the Arduino IDE “Serial Monitor” as well as telemetry to the ArxRobot App.

01           Start byte 0xA5 expected

02           Packet length out of range 1 – 20

03           LRC checksum error

04           Undefined command decoder FSM state

05           Array out of range i >= 23
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[av_heading tag=’h5′ padding=’10’ heading=’Exception Code Example’ color=” style=” custom_font=” size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]

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In this example, the camera home command is sent with an incorrect LRC byte to examine how exception codes work.

A5 01 04 00

Command Packet ID        = A5

Packet Length N                = 01

Camera Home                   = 04

Parity                                    = 00       A0 = A5 ⊕ 01 ⊕ 04

The telemetry packet (CA…) in Figure 12.1 was sent as a response from the 3DoT board when the command packet (A5 01 04 00 above) was sent. Looking at the command packet (start byte = A5), the user has sent a CAMERA_MOVE_HOME (3rd byte = 04) command with the LRC byte as 00. By calculating the LRC byte by hand (A5 ⊕ 01 ⊕ 04) it is shown that the correct LRC byte is equal to A0.

The 3DoT firmware responds to this simulated data transmission error by sending telemetry packet CA 03 0E 03 A0 64 as shown in Figure 17-1.
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Figure 17-1: Telemetry packet sent from Arduino/3Dot board.

data[i]	i = 0	i = 1	i = 2	i = 3	i = 4	i = 5
Packet	CA	03	0E	03	A0	64
Description	Packet ID	Packet Length N+1	Command Exception ID	LRC Checksum Error	Expected Checksum	Packet Checksum

The “Telemetry ID” is 0E, which is sent indicating an error was detected when trying to decode the command. 03 indicates that LRC byte sent is incorrect. In this example, A0 is the expected LRC byte that is needed to be sent. Knowing this, if the user were to send the exact same command packet, but changing the LRC byte to A0 (A5 01 04 A0), the microcontroller will not reply with a telemetry packet again.

Going back to the telemetry packet  (start byte = CA), the last byte is now the LRC byte for the telemetry packet (CA ⊕   03 ⊕   0E ⊕   A0 = 64). Again, this component is used to verify that all elements were read accurately.

It is not important understanding how to find the LRC bytes for telemetry packets, as they are automatically calculated, but it is good to know the purpose of the LRC byte for data packets for both commands and telemetry and how it is computed by the software.
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Connecting over Bluetooth can be finicky at times. If there are too many nearby sources try initially pairing to the 3Dot on your own (in isolation). If connecting still doesn’t work: first try restarting the 3Dot and rescanning Bluetooth within the app. If connecting proves to not work consistently try these steps:

1. Turn off 3Dot
2. Force Close Arxterra
3. Turn off and on Bluetooth (in phone settings)
4. Reopen Arxterra
5. Then scan for devices within Arxterra

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A bootloader is the first piece of code a microcontroller executes when it is powered ON. Usually, manufacturers burn the appropriate bootloaders into microcontroller chips prior to selling them. For instance, this is how computers recognize the type of Arduino plugged into it. However, dealing with a fresh microprocessor chip, the bootloader will have to be burned onto it before it is capable of being programmed. This tutorial will walk through how set the appropriate fuse settings and burn the 3DoT Bootloader to the board.
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[av_heading tag=’h4′ padding=’10’ heading=’Equipment’ color=” style=” custom_font=” size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]

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• AVRISP mkII compatible USB programmer
• 3DoT ICSP breakout
• 3DoT Board
• A PC with Atmel Studio 7 installed*

* Or any computer with AVRDude usable through a command line interface (advanced).
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STEP 1: Connect the AVRISPmkII to your computer. If the internal LED turns green suitable drivers are detected. If not, see “Installing MKII Driver” below.

STEP 2: Connect the 3DoT ICSP breakout to the 3DoT as shown.

STEP 3: Connect the AVRISPmkII to the breakout board. Ensure the ribbon cable is oriented to have the red wire closest to the switch and USB port.

STEP 4: Insert a battery and turn the board ON.

The external LED will light up green when the board is detected.
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If the AVR programmer is not recognized by your computer, the appropriate driver must first be installed. Download the proper driver for the AVR programmer from the web. If the AVRISP MKII driver is being used, it can be downloaded from this link. If the USBtiny AVR Programmer is being used, the driver can be downloaded from this link.

To configure AVRISP MKII Programmer to work with Arduino IDE (steps to download in section “02 – 1: Arduino IDE Tutorial”), it is necessary to install lib-win32 drivers. Extract the downloaded zip file, then follow the steps below to install AVRISP drivers:

STEP 1: Disable windows driver signature enforcement by following steps in this tutorial.

STEP 2:  Plug in the programmer to computer intended for the installation process, then open the “Device Manager”.

STEP 3:  Right-click on “AVRISP mkII” and click on “Update Driver Software”.
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STEP 4:  Click on “Browse my computer for driver software”.
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STEP 5: Make sure that “Include subfolders” is checked, then click on “Browse”.
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STEP 6: Navigate to the extracted folder (i.e. avrispmkii_libusb-win32_1.2.1.0), then click “OK”.
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STEP 7: Click on “Let me pick from a list of device drivers on my computer”.
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STEP 8: Click on “libusb-win32 devices”.
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STEP 10:  Click on “Browse” and locate “AVRISP_mkII.inf” in the “Downloads” folder.
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STEP 11: Click “Next” to close and the driver should be successfully installed.
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Now, setting the correct fuse settings can be done by two methods:
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[av_heading tag=’h5′ padding=’10’ heading=’Method 1: Using Atmel Studio 7 (Windows Only)’ color=” style=” custom_font=” size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]

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STEP 1: Open Atmel Studio 7 and click Tools -> Device Programming.
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STEP 2: The following window will appear. The tool to select is the AVRISPmkII. The device to select depends on what microcontroller is being used on your device. In the case of the 3DoT board, you will be selecting the Atmega32U4. You can find it by using the drop down menu or by typing out the name. Ensure the settings are as pictured and click “Apply”.
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STEP 3: If your device connected successfully you should see the following window. Click “Fuses”.
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STEP 4: Set the fuses as follows:

Extended Fuse: 0xCF

High fuse: 0xD8

Low fuse: 0xE2

and click “Program”. To understand what each fuse setting does, refer to the ATmega32u4 Datasheet.

A warning may pop up to change to certain fuses. These warnings can be accepted.
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[av_heading tag=’h5′ padding=’10’ heading=’Method 2: Using avrdude (All platforms)’ color=” style=” custom_font=” size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]

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STEP 1: Download and install WinAVR.

( On Linux run sudo apt-get install avr-libc avrdude binutils-avr gcc-avr srecord )

( On OS X install CrossPack and libusb)

STEP 2: Open Command Prompt (or a terminal window on Linux/OS X). Paste the following command into the command prompt.

avrdude -c avrispmkII -p m32u4 -P usb -U efuse:w:0xCF:m -U hfuse:w:0xD8:m -U lfuse:w:0xE2:m

This will configure the fuses to the setting best suited for the 3DoT board.

To customize the fuse settings, see this calculator for the possible options.
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STEP 1: Plug in the ICSP socket to the 3DoT board and jumper wires to the proper AVRISP mkII programmer pins. Then switch ON the 3DoT.

STEP 2: After switching the 3DoT ON, the LED on the AVRISP mkII programmer will change from red to yellow.

STEP 3: Open Arduino IDE and go to Tools > Programmer. Make sure “AVR mkII” is selected.
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STEP 4: Select “Arxterra 3DoT” from Tools > Board.

If the Arxterra 3DoT board is not installed in your Arduino IDE, see the “Arduino IDE 3DoT Tutorial”
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STEP 5:  Go to Tools > Burn Bootloader.
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STEP 6: Ignore the “WARNING” and wait for the Bootloader to be burned.
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Many of the labs in this document employ fast pulse width modulation (PWM) as implemented by one or more of the Atmega32U4’s four (4) timer peripheral subsystems. This chapter is included for those developers who are not familiar with fast pulse width modulation and/or the timer peripheral subsystems of the Atmega32U4.
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Pulse Width Modulation (PWM) is a technique for outputting analog voltage levels using digital means. What this means is that these pins output a square wave signal that oscillates between on and off. This oscillation essentially produces voltage levels between 0 and 5 volts depending on the duty cycle of the signal and is controlled using the “analogWrite(pin, value)” function where ‘pin’ is the pin that you are writing to and ‘value’ is a value between 0 and 255. Inputting the value 0 will result in a square wave with a 0% duty cycle and produce 0V (always off), inputting the value 127 will result in a square wave with a 50% duty cycle and produce 2.5V, while inputting the value 255 will result in square wave with a 100% duty cycle and produce 5V (always on). Any value in between 0 and 255 will result in a duty cycle between 0% and 100% correspondingly. Sample PWM signals produced with varied values can be seen below in Figure 16.1.
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Figure 16.1: Values varied for the “analogWrite()” function and their resulting PWM signal.

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PWM has several applications. A few are:

• Dimming an LED
• Providing an analog output; if the digital output is filtered,
  it will provide an analog voltage between 0% and 100%.
• Generating audio signals.
• Providing variable speed control for motors.
• Generating a modulated signal, for example, to drive an infrared LED for a remote control.

Now, there are two main operating modes of PWM: phase-correct PWM and fast PWM. To briefly explain the difference between the two, in phase-correct PWM mode the timer counter counts up and down (generating a triangle wave). When the counter reaches the compare bit, the PWM signal will be high, and when the counter counts back down below the compare bit the PWM signal will be low. Characteristics of phase-correct PWM are that the pulses are wider and that the middle of OCRnA and OCRnB are in alignment (where OCRnA and OCRnB are two separate PWM pins connected to the same timer counter) as shown in Figure 16.2.
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Figure 16.2: Phase-correct PWM.

In fast PWM mode, the timer counter counts up and then drastically drops down to zero again (generating a sawtooth wave). When the counter reaches the compare bit, the PWM signal will be high, and when the counter drops back down, the PWM signal will be low. Characteristics of fast PWM are that it is twice as fast, the pulses are narrower, and that the rising edges of OCRnA and OCRnB are in alignment as shown in Figure 16.3.
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Figure 16.3: Fast PWM.

Phase-correct PWM is the type that most of the PWM pins on the Arduino operate at, while the only pins that operate using fast PWM are the pin(s) that utilize Timer Counter 0. It is not a good idea to mess with Timer Counter 0, because this is the timer that Arduino uses to create the delay() function. However, this lab will show how to convert all PWM pins in phase-correct mode to fast mode.
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Note: This Tutorial is focused on Leonardo, needs to be refocused for 3Dot

For learning PWM modes for the 3DoT, begin with using the Arduino Leonardo since it uses the same microcontroller, the Atmega32u4. The reason this lesson will be taught on the Leonardo rather than the 3DoT is that the Leonardo has header pins which we can easily access each digital output.

There are seven PWM pins on the Leonardo. These are pins 3, 5, 6, 9, 10, 11, and 13. These pins are easily identifiable as digital pins capable of PWM by the tilde symbol (~) right next to each of these numbers. These pins belong to the following timer counters, and are pre-programmed to operate in the following PWM modes seen in Table 02 below. The digital pins that use Timer 0 and are in fast PWM mode have a frequency that is twice as fast as the frequency of the pins that are in phase-correct mode, which is consistent with what has previously been explained.
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Table 16.1: PWM modes for each digital pin on the Arduino Leonardo.

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First, set up a test code to verify that each pin on your Arduino Leonardo really produces the frequencies specified above. Download the following code.
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In this test code all the PWM pins on the Leonardo are set to output a PWM signal. Furthermore, Analog Pin 0 (though any I/O pin could be used) is set as an input to read the frequency of generated PWM pins. To test the frequency of each pin, simply start with connecting pin 3 to A0 as shown below in Figure 16.4.
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Figure 16.4: Connect pin 3 to A0.

Make sure the board is plugged in and the proper board and COM port are chosen in Arduino IDE as shown in Figure  16.5:
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Figure 16.5: Choosing the correct board and COM port.  

Upload the code to the board and open the “Serial Monitor” window as shown below in Figure 16.6:
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Figure 16.6: Opening the “Serial Monitor” window

Now, if pin 3 was started with, the frequency displayed in the Serial Monitor should be around 976 Hz, which is consistent with Table 02. Next, move on down the list of the PWM pins (5, 6, 9, 10, 11, and 13) and continue to measure the frequency of each pin. Verify that the recorded data matches up with Table 02. Please note that this Arduino frequency reader is not 100% accurate so the experimental values will be slightly off.

Next, begin converting each pin that is operating in phase-correct PWM mode to fast PWM mode. First, start with Timer 1, which generates PWM signals for pins 9 and 10. In Timer Counter 1, the PWM operating mode is controlled in the TCCR1A and TCCR1B registers as shown in Figure 16.7.
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Figure 16.7: Timer counter 1 PWM operating modes controlled by registers “TCCR1A” and “TCCR1B”.

Each pin is important and has a specific purpose but only focus on the ones with PWM operating modes which is controlled by the “WGM12”, “WGM11”, and “WGM10” bits. Table 16.2 below shows what each bit should be set to in order to achieve various PWM operating modes.
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Table 16.1: Pin values and corresponding PWM operating modes.

To achieve fast PWM, “WGM12” should be set high to ‘1’. The easiest way to do this is to use the “inbuild _BV()” function in Arduino IDE. Copy and paste the following code at the end of “setup()”. Through using the OR command, set the “WGM12” bit in the TCRR1B register high without altering any of the other bits.

TCCR1B = TCCR1B | _BV(WGM12);   // Set fast PWM for Timer Counter 1

Next, convert Timer 3, which controls pin 5, to fast PWM mode. This is very easy and similar to Timer 1. Copy and paste the following code below the line at the end of “setup()”.

TCCR3B = TCCR3B | _BV(WGM32);   // Set fast PWM for Timer Counter 3

Last, converting Timer 4, which controls pins 6 and 13, is a bit different. Its PWM functionality is controlled through the TCCR4D register as follows in Table 16.3:
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Table 16.3: Values to convert Timer 4 using the “TCCR4D” register.

So to make Timer 4 operate in fast PWM mode, clear the WGM41 and WGM40 bits in the TCCR4D register shown in Figure 16.8:
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Figure 16.8: Bits of “TCCR4D” register.

This is easily achieved through using the AND command with zeros in the place of bits ‘0’ and ‘1’ and ones for bits 7:2 in order to not manipulate any of the other bits. Copy and paste the following code at the end of “setup()”.

TCCR4D = TCCR4D & 0b11111100;   // Set fast PWM for Timer Counter 4

Run the code, open the “Serial Monitor”, and measure the frequency of each pin. You should find that the frequency of pins 5, 6, 9, 10, and 13 have doubled. Again, this is from converting each pin from operating in phase-correct mode to fast mode, which operates at twice the speed. Verify that these pins now generate PWM signals with a frequency of 976 Hz.
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WARNING Some of the information on this page is outdated, from a time when the ArxRobot Library was still named the “Robot3DoTBoard” Library. Proceed at your own risk.

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This chapters looks at 3DoT programming from a developer’s perspective. Specifically, this material is intended for developers interested in extending the capabilities of the 3DoT Library. For example how to implement a Mars rover with 6 DC motors in place of 2 DC motors assumed by the software. Before we begin you may want to review Arxterra’s three operating modes as described in “Arxterra Operating Modes.”
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This example can be easily extended to allow the control of six-wheel rovers, like our mini-sojourner.

The built-in MOVE command as the name implies, is used when you want to move your robot. This command assumes a two wheel-caster or track robot. If you are building a four wheel car where the front wheels are turned with a servo or a six (6) rover, like our mini-sojourner Mars rover, you will need to override this command.

Step 1: If you have not done so already download the code for Robot_3DoT_TeleComm (see Section “01 – 5: Sample Scripts”), rename it Robot_3Dot_Blink, and open it in the Arduino IDE. 

The “MOVE” command is defined as command ID 0x01 in the Configure.h file.

In the Robot_3DoT_Telecom example, this command is overridden and linked to the “moveHandler” subroutine located within the main file Robot_3Dot_Telecomm by the C callback statement:

A placeholder “moveHandler” subroutine is included with the example script.
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WARNING This and other example handlers include Serial write instructions which can be helpful during testing. These instructions should be deleted or disabled with a block comment (/* */) after testing is completed. Failure to do so will drastically slow the MCU performance and may result in loss-of-signal and other unexpected problems.

Step 2: For this example, I want to maintain the functionality of the built-in move instruction. To accomplish this, two motor classes need to be created. Add these two lines of code after defining the “BLINK” and “SERVO” command IDs. These will correspond to Motor A and Motor B on the 3DoT board. To better understand why these motor classes are generated, review the Motor.h and Motor.cpp files found in the 3DoT library.
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Step 3: Next, each motor will need to be initialized to their respective driver IC pins on the microcontroller. Each motor will use three pins on the TB6612FNG for control: two for direction control and one for speed control. Conveniently, these pins are already defined in the Configure.h file in the 3Dot library. To initialize these pins for control of these motors, add the following lines of code in “setup()”of the  Robot_3Dot_TeleComm file:
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Step 4: The “MOVE” command can now be programmed. Write the following code in the “moveHandler.”
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Step 5: Finally, our new move handler can be tested using the ArxRobot application or using CoolTerm. Turn off the 3DoT board and connect the motors as shown in Figure 15.1.
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Figure 15.1: Motor connection location on the 3DoT board.

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Step 6: Turn on the 3DoT board, upload the newly created code, open CoolTerm, connect the board, and open the “Send String” window.  Ok, that may be more like 5 steps.

Step 7: Input the command string shown below. Keep in mind, the order of the packet ID, packet length, command ID, parameters, and LRC byte is important. In this command string moving from left to right: A5 represents the packet ID, 05 represents the packet length (command ID + number of parameters), 01  represents the MOVE command ID, 01 represents the forward direction of motor A, 80 represents motor A operating at half speed (0x80 is 128 in decimal which is half of 255, the maximum value for PWM), 01 represents the forward direction of motor B, 80 represents motor B operating at half speed, and A1 represents the LRC byte. Send the command packet string and verify that both motors A and B are spinning forward. If the motors are not spinning forward, there could be a possible polarity issue. Simply swap the wiring connection in order to make the motor spin in reverse.
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Figure 15.2: Send Move command packet from CoolTerm.

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From experience, when using the “MOVE” command, it may be easier to set the speed to a fixed value since the direction pad on the Arxterra control panel (which uses the “MOVE” command) only controls the direction of the motors, not the speed. If the robot operates at a fixed speed, fixed PWM values can be put in the code. For example:

This would be more practical when implementing the “MOVE” command on Arxterra. When testing the code in CoolTerm, remove the hex byte for parameter ‘3’ since it is unused, while the hex byte for parameter ‘1’ does not matter. Nevertheless, it is important to keep the direction as parameters ‘0’ and ‘2’ since this is what is used for the direction pad on Arxterra.

Furthermore, now is a good time to explain that while commands for each motor to brake can be created manually using 0x03 as the direction hex byte, the Motor.cpp file in the 3DoT library defines a brake function. The following code will stop the motors:
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Try creating a command to turn motorA on for 5 seconds using “motorA.go()” in conjunction with “delay()” and “motorA.brake”. Repeat the process for motorB.
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To implement a rover you would need to add a 3DoT shield with two additional motor control chips – 6 motors total. For this class of robot, you may want to write a software slip differential drive program. Communications from the 3DoT board to the shield is implemented as an I2C interface. Software communications for this serial interface protocol is implemented by the Arduino using the “wire” library.
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In the previous sections, we have looked at adding custom command handlers. In this and the next section, we look at how to implement telemetry channels. This example adds the BATTERY_ID telemetry channel to an Arduino Uno. This channel is hardwired into the 3DoT board and when the 3DoT board is connected to Arxterra, this data stream is automatically sent to the ArxRobot application. Consequently, to show how the channel works we will need to use an Arduino Uno in place of the 3DoT board.

In the Configure.h file, the microcontroller is programmed to read the battery level from pin A5 as shown below:
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Step 1: Connect a potentiometer to the Arduino Uno with the two outer pins connected to 5V and GND, while the middle pin is connected to A5 as shown in Figure 15.4. In this circuit, the potentiometer is acting as a voltage divider to divide the 5V between the two variable resistors embedded in the potentiometer. As the potentiometer is turned to the right, the voltage output will increase and decrease as it is turned to the left.
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Figure 15.4: Fritzing diagram of potentiometer connected to the Arduino Uno.

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Step 2: Upload “Robot_3Dot_TeleComm” to the Arduino Uno and open CoolTerm. Select the “View Hex” option. As soon as the board is connected, two telemetry strings should appear. The first string is for the battery level and the second is for the motor current.

Step 3: Select “Clear Data” to clear existing data.

Step 4: The potentiometer should be dialed to the left and slowly turned to the right. The battery level telemetry will continually update as the simulated battery level changes (potentiometer). The battery levels are shown here.
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Figure 15.5: Output from CoolTerm of potentiometer connected to the Arduino Uno.

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The first byte, “CA”, is the packet ID, the second byte, “03”, is the packet length, the third byte, “06”, is the telemetry ID, the fourth byte, “00”, is an empty parameter, the fifth byte, “07”, is the parameter desired which shows the battery level in hex. The last byte, “C8”, is the LRC byte.

As shown above, when the potentiometer is turned from left to right, the following parameter values were achieved: {0x07, 0x14, 0x1A, 0x3D, 0x54, 0x59, 0x5E, and 0x63}. Translating these hex values to decimal: {7, 20, 26, 61, 84, 89, 94, and 99}. These values represent the battery level percentage. So the “battery” started at 7% and “charged” to 99%.
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In this section, we will go over the custom telemetry example provided in Robot_3Dot_TeleComm example script.

Step 1: The first step is to instantiate (“build”) a packet object named motor PWM and initialize its properties. MOTOR2_CURRENT_ID is a pre-defined telemetry channel equal to 0x02 as defined in the Configure.h text file.
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Step 2 (optional): Along with setting the telemetry ID property, the motorPWM constructor initializes both the “accuracy” and “samplePeriod” properties to their default values of 2 DN (digital number) and 1000 ms (1 second) respectively. These values should work for most robot application and no further action is needed.  In this “optional” step, these default values are changed to 1 DN  and 500 ms (0.5 seconds). Again, do not override the program’s default values unless required by your project.
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Step 3: Next, within “loop()” code segment, the sensor data is read and if the sampling criteria are met (change in DN or sample period) then a telemetry packet is sent. In the example below the “#if” conditional-compilation directive (also known as a preprocessor directive)  is chosen if a board with an ATmega32u4 (e.g., 3Dot, Lilypad USB, and Leonardo) is being used and the “#else” directive is chosen if the Uno is being used. Below demonstrates using the Uno.
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Figure 15.6: Loop code segment from Robot_3Dot_TeleComm.

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Step 4: Rather than sending a command to the motors to read the telemetry, it may be easier to manually code them for the time being. Just do not forget to remove this code later. If the Uno is being used, put code to analogWrite to pin 5.
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Without getting into the details of Pulse Width Modulation (PWM), the Arduino implements this instruction by setting the Timer 0 Output Compare Register B (0CR0B) equal to 200 (Hexadecimal C8). When Timer 0 counts up to 200 the output of Arduino digital pin 5 is cleared. Please reference Figure 15.7 for all the pins on the Uno and to which timer output pin they are mapped.
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Figure 15.7: Arduino UNO timers and corresponding output pins.

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The code within the “#else” block reads Timer 0 Output Compare Register B (0CR0B) and sets variable  “pwm_reading” equal to this value. This register value is then sent as an argument to the “sendSensor()” method.  Ultimately, the is packetized and set to via USB to the PC.

Step 5: To view this packet, open CoolTerm, connect the board, and View Hex. A similar reading as shown in Figure 15.8 should appear.
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Figure 15.8: Telemetry sequence showing value of the 0CR0B register.
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In Figure 15.8, the first telemetry sequence is the battery telemetry, and can be disregarded for now. The second telemetry sequence, which is boxed in red, is the 0CR0B value in hex (0x00C8). In decimal this is 200, which not surprisingly, is the value sent as the second argument in the analogWrite instruction. Now, this telemetry is meant to be implemented to read the current of a motor, while right now, it is only reading a PWM value that was written.
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