382-Lab-7 - Using IR Sensors With LEDs

Objectives

The goal of the lab was to use the three IR sensor/receiver pairs on the bot to detect if objects were close by, and, if so, turning on the corresponding LED (left, right, both for center).

Preliminary design

Software flow chart

1. Define Threshold constants
2. Setup ADC10 on the MSP430 (main)
3. Establish LED's as output (main)
4. Sample ADC10 input channel (for loop)
5. Convert reading to a voltage (for loop)
6. Compare voltage to threshold for respective side (for loop)
7. Turn LED on or off (if statement)
8. Repeat for each channel (for loop)
9. Infinite for loop (4 to 9)

Hardware schematic

Well-formatted code

/***
 * Sean Gavan
 * 8 Dec. 14
 * Lab 7 -- Detecting walls with IR sensors
 * For this lab we were to use the IR transmitter/receiver pairs to detect when obstacles were near the bot.
 * Documentation: I asked Capt. Trimble on multiple occassion how to fix some issues with the green LED
 * always staying on.
 */
#include <msp430.h> 

/*
 * main.c
 */
int THRESHOLDLEFT = 0x3B0;		// Threshold voltage for wall prescence
int THRESHOLDRIGHT = 0x0FF;
int THRESHOLDCENTER = 0x3D0;

void main(void) {
    WDTCTL = WDTPW | WDTHOLD;				  // Stop watchdog timer
    ADC10CTL0 = ADC10SHT_3 + ADC10ON + ADC10IE; 		  // 64 ADC clks to combat loading, ADC10ON
    ADC10AE0 |= BIT1 + BIT2 + BIT4;           // P1.1, P1.2, P1.4 to ADC mode (A1,A2,A4)
    ADC10CTL1 |= ADC10SSEL1|ADC10SSEL0;       // Select SMCLK
    P1DIR |= BIT0 + BIT6;

    for (;;) {
    	ADC10CTL1 = INCH_4;				// Right receiver A4
    	ADC10CTL0 |= ENC + ADC10SC;
    	__bis_SR_register(CPUOFF + GIE);        // LPM0, ADC10_ISR will force exit
    	if (ADC10MEM > THRESHOLDRIGHT) {
        	P1OUT |= BIT6;				// P1.6 on
     	} else {
     		P1OUT &= ~BIT6;				// P1.6 off
     	}

    	ADC10CTL1 = INCH_1;				// Left receiver A1
    	ADC10CTL0 |= ENC + ADC10SC;     // Sampling and conversion start
    	 __bis_SR_register(CPUOFF + GIE);        // LPM0, ADC10_ISR will force exit
    	if (ADC10MEM < THRESHOLDLEFT) {		// Wall close (less V when wall close)
    		P1OUT |= BIT0;             // P1.0 LED on
    		P1OUT &= ~BIT6;
    	} else {						// Wall close
    		P1OUT &= ~BIT0;              // P1.0 LED off
    		P1OUT &= ~BIT6;
    	}

    	ADC10CTL1 = INCH_2;				// Center receiver A2
    	ADC10CTL0 |= ENC + ADC10SC;
    	 __bis_SR_register(CPUOFF + GIE);        // LPM0, ADC10_ISR will force exit
    	if (ADC10MEM < THRESHOLDCENTER) {
    		P1OUT |= BIT0 + BIT6;				// Both on
    	} else {
    		P1OUT &= ~(BIT0 + BIT6);			// Both off
    	}
   }
}

// ADC10 interrupt service routine
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void)
{
	ADC10CTL0 &= ~ENC;
  __bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)
}

Debugging

ADC10MEM not changing for each input channel. FIX: Declare input channel individually. INCH_X refers to what the active channel is. Each channel has to be declared and then sampled individually in order to get each ACD10MEM value. I also added the interrupt included in the class notes so that there would be time to stop samping and convert the signal to a voltage.

Testing methodology

Ran the program through the debugger to see how ADC10MEM would change - found that the center and left receivers would read a lower voltage as an object got closer as opposed to the higher-voltage-if-a-wall-is-closer idea. Right receiver worked normally. This also changed the threshold values since each receiver was different. I had to find the base line voltages and then the voltages for when a wall was close to each receiver. This resulted in the threshold constants in the above code.

Observations

From the lab, I've been able to see how useful an analog-to-digital conversion system can be. Being able to sense where walls are, in this case, can be a small part in an even greater project. This will be especially helpful in Lab 8, where this system, in conjunction with the motors, will guide the bot through a maze

Documentation

I used the class notes as a template for coding the ADC10 on the MSP430.