Difference between revisions of "S14: Need For Speed"

Revision as of 16:10, 24 May 2014

Abstract

Android RC Car

This page contains design and implementation of our Embedded Software project, Need For Speed. It's about maneuvering an RC vehicle using the Acceleration Sensor in a smart phone. An Android Application is developed to transmit the Acceleration Sensor Signals to the vehicle via Bluetooth. The car is mounted with a Bluetooth module to receive data from the phone. And the acceleration and turning of the vehicle will be based on this data. The vehicle is also mounted with two Infrared Sensor modules for collision detection, one in the front and other in the rear.Detection of any obstacle in the vehicles path will bring the vehicle to a halt state immediately.

Introduction

Logo for our Android App

In this project we are using JY-MCU Bluetooth module to be the wireless link between the smartphone and the battery powered RC vehicle. The Android application is developed to transmit a particular byte for every threshold value of the Acceleration Sensor i.e. when the phone is one byte for front tilt and another for back. This received byte is compared by the SJOne board with few predefined values and accordingly PWM signals are given to the motors.

The input of the IR sensors is connected to the hardware interrupts on the SJOne board, the interrupt subroutine will be called every time there is an obstacle in the path of the vehicle, this subroutine will in turn stop the vehicle.

Objectives

As this project is both software and hardware based, our objectives were as follows;

• Hardware Objectives
  • To achieve a constant 6V DC supply for the motors and 5V DC for the board from the battery.
  • To interface the motors to the SJOne board via L298 motor driver.
  • To calibrate the IR sensors to sense obstacle in 6" proximity.
• Software Objectives
  • To develop an Android application to send the data from Acceleration Sensor via Bluetooth.
  • To develop a FreeRTOS code to receive these signals and process them.
  • To develop a FreeRTOS code to send PWM sigal to the motor for variable speed.
  • To develop a FreeRTOS code to accept interrupt from the IR sensors and take actions accordingly.

Team Members & Responsibilities

• Amey Patil
  • Hardware Design
  • Free RTOS (Part 1: To interface motors and LPC1758 using PWM)
  • Free RTOS (Part 2: To configure the Bluetooth module)
• Siddhata Patil
  • Free RTOS (Part 3: To send and receive data between Bluetooth module and LPC1758)
  • Android Application(Part1: To send data from Android Phone to LPC1758)
  • Android Application(Part2: To send results of accelerometer sensor from Android Phone to LPC1758)

Schedule

Parts List & Cost

Design and Implementation

System Block Diagram

The above Block Diagram shows the overall implementation of the project. The accelerometer values (x, y, z) are used as an input by the android application. Depending on the instantaneous values, tilt will be determined. This tilt value will be provided to the Bluetooth for transmission. At the receiver, this tilt data will be received by the Bluetooth Module and provided to the LPC 1758 board via an UART channel. The on board processor will compare the received data with the stored values and generate PWM signals accordingly. The motor driver upon reception of this will driver the vehicle in the respective direction. We will see detailed explanation of the hardware and software in their respective sections.

Hardware Interface

Let us understand the whole structure piece by piece.

1. LPC 1758 SJOne Board

This board was a part of our course on Embedded Software at San Jose State University. For more information on the SJOne board Click_me.

Power Supply Schematic.

2. Power Supply

We need to generate steady 5V supply for the board while 6V for the motors without any current limitation otherwise the motors will not give its optimum output. To our luck, LM7806 voltage regulators are also available in the market along with the LM7805. The circuit schematic is as shown in the figure above.

The total current requirement of the circuit is around 1Amp. If this much current is to be drawn through the regulators then we must make sure the heat generated is properly dissipated, so we use heat sink. Most of the current will be driven through the LM7806 regulator as it drives the motors hence, we made sure that it is not surrounded by any other component. As, the LM7805 regulator just drives the SJOne board and IR module, current flowing through it is around 100mA. Hence, this regulator won't heat as much as the other one.

Motor Driver Schematic.

3. L298 Motor Driver

You must be thinking why didn't I use L293D as it is best for 6V motors and much easy to interface. Well, one of our motor consumes 200mA of current, which makes the total current 800mA that too in no load conditions. With load it might have seared upto 1A. Now the maximum handling capacity of L293D is 1A while that of L298 is 2A. Hence, for safety reasons I went for L298 motor driver. The pin connect for this interface is as shown in the above figure. The functions of the pins are as follows;

IN1 receives 'PWM input for left motor +' from LPC 1758 and drives OUT1

IN2 receives 'PWM input for left motor -' from LPC 1758 and drives OUT2

IN3 receives 'PWM input for right motor +' from LPC 1758 and drives OUT3

IN4 receives 'PWM input for right motor -' from LPC 1758 and drives OUT4

SENSE A limits the current for Left Motor

SENSE B limits the current for Right Motor

VS: Supply voltage for the Motors

For more information on L298 Driver, Click_me.

IR Module Schematic.

4. IR module

The IR module we are using is custom made. It is is designed to output logic '1' if any obstacle is detected or else logic '0'. The output signal from the IR receiver is directly proportional to the amount of IR waves falling on it. Hence, the output voltage for an obstacle far from the receiver will be less than that of a closer object.

In any case this output is in millivolts hence, we gave it as an input to LM358 which is a dual op-amp IC. This op-amp is configured in comparator mode. When the input at the non-inverting terminal is higher than the threshold voltage provided to the inverting terminal, the op-amp will give a logic high output. Hence, the threshold voltage is inversely proportional to the distance of the obstacle. So we connected a potentiometer at the input of the threshold voltage by which we can vary the range of obstacle detection.

In the case of IR the sensitivity of the reciever is not sufficient to detect obstacle at a longer distance. We were able to acheive obstacle detection in 2 inches of proximity. If, you are looking for detection at a longer distance, we would suggest you to go for Ultrasonic sensor modules which can even give you the distance of the obstacle from the vehicle.

Figure shows the circuit schematic of the IR module. This is circuit for one of the IR module. Two such circuits are implemented for front and back.

Bluetooth Module

5. Bluetooth Module

The module has 4 pins labeled on the back, VCC, GND, TXD and RXD. You might buy a module with two more pins KEY and STATE but it won't matter if you leave them open. The controller which it is interfaced with considers it as an serial UART device. So make sure you connect the RX and TX of the controller with TXD and RXD of the bluetooth module respectively.

This module works best if you are running on 3.3V, in case you are working on TTL logic then you might use a voltage divider for proper operation of the module. According to the datasheet the VCC pin is capable to handle supply ranging from 3-6V so it is fine to give TTL logic supply but, do not give TTL logic signal to the RXD pin, it cannot take anything more than 3.3V, doing such will damage the pin and hence the module.

The communication for configuration of the module is based on AT commands. There is one command for every thing, to set the device name, set the pin, set the baud rate and much more. All you have to do is to save these AT commands in the form of string and send each byte serially to the module using a simple for loop. Initially the baud rate is set to 9600. Following table shows few of the AT commands which you may require.

FreeRTOS Programming

Whenever a character is sent by the Bluetooth module, the UART interupt handler code is executed. The code is attached below.

Android App Developement Design

Controller stage in Progress

Circled is our Android App

Using Android SDK

Android Application Developement was new to both of us. So we started with basic lectures on Android SDK. In our Android Application our objective was to pair bluetooth device on our phone with the bluetooth module that we used with SJOne Board. For pairing of devices we used the search and scan method of bluetooth devices insted of using IP address. Thus making it more User friendly. Once the pairing was done successfully we went to the next step, which was designing of Controller for the RC Car. In this process we designed lots of controllers like remote based controller, joystick based controller and finally settled to the motion controller with the help of the in built accelerometer sensor of the android device. This was done using tilting motion of the android device. Here the device was calibrated such that the parallel position with respect to ground was considered zero position.

Bluetooth Pairing

Joystic controller in motion

Accelerometer Controller screen

Testing the Android Application

Testing on Hercules

The Testing was carried out by using the android device in developement mode. In this mode, we had enabled USB debugging which allowed us to run our Android Application directly on our Android Device, thus saving lot of our time due to the slow emulator. When the project was build successfully, the APK file was then transfered to another android device and thus double testing was carried out. After the Android Application was ready, it was time to test the interface of the hardware. For this, we had to first check whether the android device was able to send data to the SJOne Board via bluetooth. This was done by connecting the SJOne Board to the Laptop. The result were seen on Hercules. If you enlarge the image you can see various numbers which show a successfull sending of the data. We have conditions like Forward, Backward, Right, Left and Halt. Each one is assigned a different integer value as seen in the screenshot.

Android App Package

In our Android App Package, CMPE_244_NEED_FOR_SPEED, we have developed two activities. Our first Activity is the MainActivity which searches all the Bluetooth Devices possibly available and pairs the one we click on. For this purpose we have used the scanning of devices method instead of the IP Address technique. Once the pairing is successful, it will go to the next activity which is JSActivity which sends charachters and integers via bluetooth to the SJOne Board. This different data are send with the help of accelerometer Sensor in the Android Device. This is done by tilting the device. These sensor values were calibrated using the code in JSActivity. For accelerometer results, we find values of x, y and z values. These values are thus converted into integers and send via Bluetooth. We have made many projects before, until we finalized this one. We also made one spare application, in which we had a joystick kind of controller. This was done using Android Widgets. But we liked the accelerometer android app more and decided to go with it. Thus for this app, we have two files in source folder, one is MainActivity.java and other is JSActivity.java. Their corresponding xml file were written in Relative Layout format. One is activity_main.xml and other is remote_active.xml. And finally in AndroidManifest we declare the MainActivity first and after that we declare the JSActivity.

References

Thanks To...

• Preet Kang: Lecturer

Datasheets

• [1] Philips Semiconductors. LPC214x datasheet. August 2006.
• [2] Robot Electronics. SRF02 ultrasonic range finder datasheet. Retrieved from http://www.robot-electronics.co.uk/htm/srf02techI2C.htm

Appendix

• [Project source code is available at SourceForge]
• [Project Demonstration Video]