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Michael Barbosa-Aguayo

Published February 12, 2019

Anteater Electric Racing at UC Irvine

Embedded systems development of an Formula SAE Electric Racecar at the University of California, Irvine.

IntermediateWork in progress763

Things used in this project

Hardware components

Texas Instruments MSP430G2ET

Rotary potentiometer (generic)

Software apps and online services

Texas Instruments Code Composer Studio

Hand tools and fabrication machines

Soldering iron (generic)

Story

Driver Input Module

What is the Driver Input Module?

The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) micro-controller with the requirements of handling driver input of Lithium, UC Irvine’s 2019 FSAE Electric Racecar competing in Lincoln, Nebraska. The driver input includes two independent Accelerator Pedal Position Sensors (APPS), one Brake System Encoder (BSE), and one Steering Angle Position Sensor (SAPS). These inputs are processed by the DIM, and pulse-width-modulation (PWM) signals are calculated and sent to their respective motor controller. These signals are computed using a torque vectoring algorithm which increases the torque to the outside wheel during a turn.

Context of the DIM:

The figure below describes the context of the DIM. The driver input sensors (APPS, BSE, and SAPS) are analog potentiometers ranging from 0V-5V connected to the Analog-to-Digital Converter (ADC) of the DIM. The DIM utilizes this input data to check for faults in the system on a software level, and to calculate the two independent throttle signals sent to the motor controllers. The voltage and ground are switched for the Accelerator 2 potentiometer due to the need for the Accelerator 1 and Accelerator 2 input signals to have different transfer functions. The different transfer function is accounted for in the software.

Diagram showing GPIO connections of MSP430G2ET with peripherals

Description of the Faults:

“Faults” were previously mentioned and are critical to the design of the DIM for a tech-ready racecar. Faults can arise if the accelerator (depressed at >20%) and brake pedal are actuated at the same time, if there is a floating input voltage in either sensor, or if there is different APPS voltages between the two independent inputs. These faults are defined as a “plausibility” by the FSAE rulebook, and must be accounted for in our Failure Mode Effect Analysis (FMEA). If a plausibility occurs, the DIM will send throttle values of zero until the fault is cleared.

Why is DIM important?

The DIM is essential for Lithium to be safe and tech-ready for final competition in Lincoln, Nebraska. This system is used to detect faults to prevent the racecar from transmitting incorrect pedal values for safe operation. Furthermore, the DIM provides hands-on experience with a micro-controller for UC Irvine undergraduate Computer Engineers. DIM has been in development since the beginning of Fall 2018 quarter and is expected to be integration ready by February of 2019.

ADC input values are used to modulate two different PWM outputs to the motor controllers

Updates:

2/12/2019

First iteration of DIM complete (ADC input, PWM output).
Design phase has begun for implementing CAN Bus communication utilizing MCP2515 CAN Controller and TJA1050 CAN Transceiver. This will modularize the embedded system by allowing communication between multiple micro-controllers.

Code

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/


//returns 1 if fault, 0 if no fault. (checks acc pedal transfer functions)
int APPS_Fault(int,int);

//returns 1 if BSE fault, 0 if no fault (checks that acc is not depressed when brake is depressed >10%)
int BSE_Fault(int,int,int);

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

#include <ADC.h>
#include <Faults.h>
#include <PWM.h>
#include <msp430g2553.h>
#include <stdint.h>


int steeringval;
int accval;
int acc2New;

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;   // stop watchdog timer
    BCSCTL1 = CALBC1_16MHZ; // Set range
    DCOCTL = CALDCO_16MHZ;
    init_ADC();		//initiate ADC 
    init_PWM();		//initiate PWM
    while (1) {
		read_ADC();		//read input from potentiometers
		
        if(APPS_Fault(acc1Input,acc2Input) || BSE_Fault(brakeInput,acc1Input,acc2Input)){
           AcceleratorL = 0;		//Set throttle signals to 0 if fault occurs
           AcceleratorR = 0;
           setThrottleValue(AcceleratorL,AcceleratorR);
        }
        else {
			int accel = acc1Input;
			float B = 0.4; // offset of curve for torque vectoring
			float A = 0.6/(72); // slope of curve for left  turn torque vectoring
			float D = 0.6/(77); // slope of curve for right turn torque vectoring
			steeringval = steeringInput; //steering potentiometer value
			//TORQUE VECTORING BASIC ALGORITHM
			if (steeringval < 373 && steeringval > 84) { //left turn calibrated for 20% margine b4 turn engaging
				AcceleratorR = accel *( A*((512-steeringval) - 84) + B)*0.605; //calibrated so it is 40% at full turn
				AcceleratorL = accel*0.605;
            }
			else if (steeringval < 84){
				AcceleratorR = 1023*0.605;
				AcceleratorL = accel*0.605;
			}
			else if (steeringval > 534 && steeringval < 842) {                 //right turn calibrated for 20% margine
				AcceleratorR = accel*0.605;
				AcceleratorL = accel *(D *(842-(1023-steeringval)) + B)*0.605;  //calibrated so it is 40% at full turn

			}
			else if (steeringval > 842){
				AcceleratorR = accel*0.605;
				AcceleratorL = 1023*0.605;
			}
			else { //on center steering.
				AcceleratorR = accel*0.605;
				AcceleratorL = accel*0.605;
			}

			setThrottleValue(AcceleratorL,AcceleratorR);		//Sends accelerator signals for PWM output
		}
    }
}

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

#include <msp430g2553.h>
#include "PWM.h"

void init_PWM(){
    P2DIR |= BIT1;
    P2SEL |= BIT1;
    P1DIR |= BIT6;
    P1SEL |= BIT6;

    TA1CCR0 |= 624;  //625 is the period for 1.6kHz so value is 0-624
    TA1CCTL1 |= OUTMOD_7;
    TA1CCR1 |= 0;   //initialize PWM at 0 duty cycle
    TA1CTL |= TASSEL_2 + MC_1;

    TA0CCR0 = 624;	//625 is the period for 1.6kHz so value is 0-624
    TA0CCTL1 = OUTMOD_7;
    TA0CCR1 |= 0;	//initialize PWM at 0 duty cycle
    TA0CTL |= TASSEL_2 + MC_1;
}

void setThrottleValue(int accL, int accR){
    if(accL < 5){
        accL = 5;
    }
    else if(accL > 1015){
        accL = 1015;
    }
    if(accR < 5){
        accR = 5;
    }
    else if(accR > 1015){
        accR = 1015;
    }
    TA1CCR1 = accL;
    TA0CCR1 = accR;
  //      __bis_SR_register(LPM0_bits);
}

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

int AcceleratorL;  //Left motor duty cycle
int AcceleratorR;  //Right motor duty cycle

__interrupt void Timer_A0_CC0(void);
__interrupt void Timer_A1_CC1(void);

void init_PWM();

void setThrottleValue(int , int );

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

#include <ADC.h>
#include <msp430g2553.h>

// ADC10 interrupt service routine
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(ADC10_VECTOR))) ADC10_ISR (void)
#else
#error Compiler not supported!
#endif
{
  __bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)
}

void init_ADC(){
    ADC10CTL1 = INCH_3 + CONSEQ_1; //Channel 5 down to 0  and sets up single channel conversion
    ADC10CTL0 = ADC10SHT_2 + MSC + ADC10ON + ADC10IE;
    ADC10DTC1 = 4;
    ADC10AE0 = BIT3 + BIT2 + BIT1 + BIT0;   //enables analog on pin 1.0, 1.3, 1.4, and 1.5
}

void read_ADC(){
    ADC10CTL0 &= ~ENC;
    while(ADC10CTL1 & BUSY);
    ADC10SA = (unsigned int)adc;
    ADC10CTL0 |= ENC + ADC10SC;
    __bis_SR_register(CPUOFF + GIE);

    steeringInput = adc[0];
    brakeInput = adc[1];
    acc1Input = adc[2];
    acc2Input = adc[3];
}

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

unsigned int adc[4];
int acc1Input;
int acc2Input;
int brakeInput;
int steeringInput;


__interrupt void ADC10_ISR(void);

void init_ADC();
void read_ADC();

/*
Component: Driver Input Module
Engineer: Lucas Juttner
Company: UC Irvine Anteater Electric Racing
Date: February 12, 2019
Description: The Driver Input Module (DIM) is a Texas Instruments MSP430G2ET (implemented with a G2553 integrated circuit) 
micro-controller with the requirements of handling driver input of Lithium, UC Irvines 2019 FSAE Electric Racecar 
competing in Lincoln, Nebraska. 
*/

#include <Faults.h>
#include <stdint.h>

int BSE_flag = 0;
//returns 1 if fault, 0 if no fault. (checks acc pedal transfer functions)
int APPS_Fault(int acc1, int acc2){
    //102 is 10% of 1023 which is the max value for ADC inputs
    //if acc1 or 2 is <10 then there is a disconnect on the line since it is pulled down.
    //if apps flag has been already triggered but fault is still occurring, do nothing
    acc2 = 1023 - acc2;		//Accelerator 2 potentiometer has a negative transfer function to Accelerator 1
    if((abs(acc1-acc2) > 102) || (acc1 < 10) || (acc2 < 10)) {
        return 1;
    }
    //if there is no fault occurring, disable APPS flag if it is triggered and continue execution.
    else {
        return 0;
    }
}

//returns 1 if BSE fault, 0 if no fault (checks that brake is not depressed when acc is depressed >25%)
int BSE_Fault(int brakeAngle, int acc1, int acc2){
    acc2 = 1023 - acc2;		//Accelerator 2 potentiometer has a negative transfer function to Accelerator 1
    if((BSE_flag) && (acc1 > 51 || acc2 > 51)) { //51 is 5% of 1023
        return 1;
    }
    if((acc1 > 256 || acc2 > 256) && brakeAngle > 542){ //256 is 25% of 1023      542 is 53% of 5V where 2.67V is "hard press" of brakes
        BSE_flag = 1;
        return 1;
    }
    else if ((BSE_flag) && (acc1 < 51 && acc2 < 51)){ //51 is 5% of 1023  if flag is already set, flag will clear when APPS values are less than 5%
        BSE_flag = 0;
        return 0;
    }
    return 0;

}

Credits

Comments

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Anteater Electric Racing at UC Irvine

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Driver Input Module

What is the Driver Input Module?

Context of the DIM:

Schematics

Circuit Diagram

Code

Faults.h

main.c

PWM.c

PWM.h

ADC.c

ADC.h

Faults.c

Credits

Michael R. Honar

Lucas Juttner

Rieli Tjan

Saipraneeth Muktevi

Tom

Michael Barbosa-Aguayo

Comments

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Anteater Electric Racing at UC Irvine

Anteater Electric Racing at UC Irvine

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Driver Input Module

What is the Driver Input Module?

Context of the DIM:

Schematics

Circuit Diagram

Code

Faults.h

main.c

PWM.c

PWM.h

ADC.c

ADC.h

Faults.c

Credits

Michael R. Honar

Lucas Juttner

Rieli Tjan

Saipraneeth Muktevi

Tom

Michael Barbosa-Aguayo

Comments

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