By: Xiong Lee (Systems Engineer)

Introduction to Arxterra App:

We first had to download the Arxterra App by emailing Jeff Gomes to give us the invitation to download Arxterra. The app has two modes we can access. The first one is remote control and the other is community. The remote control mode allows us to control the movement of the pathfinder from the Arxterra app on your phone. The community mode allows us to control the pathfinder through the control panel online found here. For our purpose, we wanted to be able to communicate with app via bluetooth so we used the remote control mode to show Bluetooth connection. To learn more about the features of the app, the video is shown here.

Code:

The code that was used to test the Bluetooth connection to the Arxterra app is found here. This code was the latest code we could find that was used for this pathfinder. There was trouble having the code work. The first problem we came up with was not having all the library files so the code could not compile. The files that we needed in the library was found on GitHub and was implemented into our Arduino IDE library. The libraries on GitHub can be found here. To add libraries to the arduino, you can go here.

Debugging the code:

     if (cmd == MOVE) {

       /***********************************

       * motion command = 0x01

       * motordata[3]   left run    (FORWARD = index 1, BACKWARD = index 2, BRAKE = index 3, RELEASE = index 4)

       * motordata[4]   left speed  0 – 255

       * motordata[5]   right run   (FORWARD, BACKWARD, BRAKE, RELEASE)

       * motordata[6]   right speed 0 – 255

       * example

       * forward half speed  0x01, 0x01, 0x80, 0x01, 0x80 0101800180

       ***********************************/

       /*

       WARNING

       WARNING ONLY THE TB6612FNG HAS BEEN UPDATED WITH NEW INDEX ADDRESSES

       WARNING Typically all you need to do is add 2 to the index (1 -> 3, 2 -> 4, etc.)

       */

         // Pololu VNH5019 motorshield (Pathfinder)

//          move_VNH5019(data);

       //collisionDetection = (data[1] == 1) || (data[2] == 1);  // set to true if any motor is moving forward

     }

After finding all the libraries that we needed, we uploaded the code to the microcontroller. When testing the code, it did not move at all. From the picture above, we can see that the app is sending command packets to the arduino, but it is still not moving. So in conclusion, we knew that the code was not decoding the commands correctly and had to run over the code and debug it.

While running through the code, we found out that the move command was not being called in the command tab. When going to the move command, there was no command there to tell the pathfinder what to do because we have the pololu VNH 5019 motor shield on the pathfinder. The move routine was commented out and not calling the pathfinder to move. So after uncommenting this command (the code highlighted in red above), we also needed to uncomment the move subroutine on the first tab (arxrobot firmware).

//void move_VNH5019(uint8_t * motordata)

//{

//  int m1Speed = dirArray[motordata[1]] * motordata[2]; // left motor

//  int m2Speed = dirArray[motordata[3]] * motordata[4]; // right motor

//  md.setSpeeds(m1Speed, m2Speed);

//}

Another problem with the code was in the move_VNH5019 routine. The motordata[ ] should be in the order of 3,4,5,6. So instead of the code you see up there, it should be

 int m1Speed = dirArray[motordata[3]] * motordata[4]; // left motor

 int m2Speed = dirArray[motordata[5]] * motordata[6]; // right motor

 md.setSpeeds(m1Speed, m2Speed);

Bluetooth connection on Arduino board:

Their Bluetooth chip (HC-06) was connected on the previous pathfinder’s custom  PCB. In the code, the ports that the Bluetooth chip is reading on the Arduino board was the serial port 2. This means that the Bluetooth chip need to be connected to the RX2 and TX2. Since the chip was on the PCB, we couldn’t tell if it was connected to the right port and so we decided to disconnect the PCB and jump wire the Bluetooth to the ports using a breadboard instead.

Conclusion:

Another error came into factor when we still couldn’t get it to work. The other error was that the batteries were low and couldn’t run the motors. So we charged the batteries and after doing all the debugging and rewiring, we finally got the arxterra app to work via bluetooth. We made the pathfinder move using the remote control mode. The things we learned were to not expect the codes to work right away. We had to learn how the commands were transferred through the app and how it was decoded. We had to assume the bluetooth chip was not connected to the RX2 and TX2 pin because we couldn’t tell if their custom PCB was working properly. In the end, we were able to get the Bluetooth connection to work with the Arxterra App.

Source Materials:

http://arxterra.com/control-panel/  

https://www.youtube.com/channel/UCJXZGMpv8GqxkOi6W02GzoQ

https://github.com/arxterra

http://arxterra.com/pathfinder-axterra-gps-communication-part-three/

https://www.arduino.cc/en/Guide/Libraries

by: Tuong Vu (Sensors, Actuators and Power)

Introduction:

This document is to explain the charging control circuit of the pathfinder. The customer wants the pathfinder to have a self-charge capability. This circuit will help regulate voltage and circuit during the charging time of the batteries by the solar panel. The purpose is to prevent the damage to the batteries from overcharging.

Electronic Components:

• 2 X resistors 1k ¼ watts
• solar panel : NPower Amorphous Solar Panel Battery Maintainer Kit – 2.5 Watts
• 2 X batteries : 10000MAh lead Battery
• N- channel IRF840

Understand Components:

Figure 1

  According to the diagram above, two pins are reserved for this circuit from the Arduino, specifically   one analog pin and the other digital pin.  Analog pin is used for the intake voltage data from the voltage divider.  We implement the voltage divider to prevent damaging the I/O pins on the arduino, see table 1.  Ideally  the mosfet acts like switch such when voltage into the gate is much higher than the threshold voltage, the mosfet turns on, which means the drain and source  pins  are in series together. Arduino can generate a 5 volts output, which is enough to turn the mosfet on. When the  drain and source are connected the solar panel  is directly in  series with  the battery, allowing the current to flow and effectively charging the battery.

The batteries and the solar panel switch place

Arduino Code:

Code  generates a  sequence of  addition   of  input voltage  taken from the  voltage divider,  which  will  go through  an if statement  in order  to   turn  the  Mosfet  on.

/*————————————————————–

Program:       Volt_measure

Description:  Reads value on analog input A2 and calculates

The voltage assuming that a voltage divider

Network on the pin divides by 11.

Hardware:     Arduino Uno with voltage divider on A2.

Software:      Developed using Arduino 1.0.5 software

Should be compatible with Arduino 1.0 +

Date:             22 May 2013

Author:          W.A. Smith, http://startingelectronics.org

————————————————————–*

// number of analog samples to take per reading

#define NUM_SAMPLES 10

int sum = 0;                // sum of samples taken

unsigned char sample_count = 0; // current sample number

float voltage = 0.0;                  // calculated voltage

int r8 = 8;

void setup()

{

Serial.begin(9600);

pinMode(r8,OUTPUT); // output pin.

}

void loop()

{

// take a number of analog samples and add them up

while (sample_count < NUM_SAMPLES)

{

sum += analogRead(A0);

sample_count++;

delay(10);

}

// calculate the voltage

// use 5.0 for a 5.0V ADC reference voltage

// 5.015V is the calibrated reference voltage

voltage = ((float)sum / (float)NUM_SAMPLES * 5.015) / 1024.0;

// send voltage for display on Serial Monitor

// voltage multiplied by 11 when using voltage divider that

// divides by 11. 11.132 is the calibrated voltage divider

// value

Serial.print(voltage * 11.132);

Serial.println (” V”);

sample_count = 0;

sum = 0;

if  (voltage < 4)

{

digitalWrite(r8,HIGH);

//delay(5000);

}

else if ( voltage > 4)

{

digitalWrite (r8,LOW);

//delay(5000);

}

}

//delay(100000)    .

This code was written by W.A. Smith, but is modified with the if statement by us. The Arduino is taking samples and applying them through the equation in the code ( see code) thus gives the voltage increment  we need. The output voltage generated by the arduino is the 8  digital pin,  this is where  the mosfet going to get the voltage to turn on or off.

figure 2 ATmega 328P specifications

Test results

The above picture shows that the battery has 5.04 V before charging

This picture shows that the battery now has 7.77 V after charging

Source Materials:

Arduino: Read Analog Voltage click here

NASA: How do Photovoltaics Work? click here