Team M&P430: Megin Budacki, Peyton Huene

Published December 28, 2019

The Tile Tapper

A TI MSP430-based robot that uses photoresistors to sense piano tiles and servo motors to tap them on an iPad screen.

IntermediateFull instructions providedOver 1 day713

Things used in this project

Hardware components

Hitec HS-311 Servo Motor

Photoresistor

Resistor 2.21k ohm

Apple iPad

iPad Stylus

Software apps and online services

Piano Tiles

Texas Instruments Code Composer Studio

Tera Term

Hand tools and fabrication machines

Creality Ender 3

Soldering iron (generic)

Laser cutter (generic)

Vertical Bandsaw

Story

Introduction

The Tile Tapper is an entirely TI MSP430-controlled robot designed to play the iPad application "Piano Tiles". To do this, photoresistors are used to determine whether a given tile passing across the screen is black or white. This information is then used by the four corresponding motors to tap the styluses and hit the tiles at the correct time.

Figure 1: Team M&P430 with the Tile Tapper

TheCode

Timer A: Happening in the MSP430 Timer A, the ADC10 DTC (Analog-to-Digital Converter, Data Transfer Control) is used to read the four photoresistors and send their values to a global four element integer array once every 0.5 ms. In the ADC10 ISR (Interrupt Service Routine), these four photoresistors are correlated with specific motors and given thresholds for their readings. These thresholds determine whether the motor is seeing white or black, and thus whether the stylus should be tapped on the screen or not.

Timer B: Happening simultaneously in Timer B, the "up" or "down" commands are used to set the duty cycle for manual PWM signals using digital I/O pins for each motor. The clock is looping a counter every 20 ms in order to create a PWM frequency of 50 Hz, as is required by the servo motors.

MechanicalDesign

The initial prototype was made using card board, zip ties, and glue for rapid assembly. This allowed for effective proof of concept and ultimately determined the placements for the motors, photoresistors, and wire lengths for the final design. In Figures 2 and 3, the cardboard prototypes for both the photoresistor holder and the motor casing are shown. For the final design, 3D printing was used to fabricate the casing that holds the motors in place. Acrylic was cut and used to hold the photoresistors above the tile columns to read the tiles in each of the four rows. The final prototype is shown in Figure 4.

Figure 2: Photoresistor threshold testing

Figure 3: Initial cardboard prototype

Figure 4: Final prototype

PainPoints

Software:

The most prominent issue to be tackled during this project was the limited number of timers available on the MSP430. Knowing that Timer A would ultimately be used solely for reading photoresistors and storing them globally using the ADC10 DTC, determining how all four servo motors would be controlled using PWM signals within one timer became a challenge. This challenge was ultimately tackled by manually setting digital I/O pins high and low with the right timing to create the necessary PWM signals for the motors.

The next challenge was determining a proper speed for the timer. Initially a clock period of 0.1 ms was used for both timers so the photoresistors would update quickly and the servo motors would respond nearly immediately. Servo motors expect an input signal with frequency 50 Hz, or a period of 20 ms. Using a clock period of 0.1 ms allowed us to use 200 clock cycles to produce our PWM period. The full range of the servo motors can be controlled using PWM duty cycles from 3% - 13%, or 6 - 26 clock cycles high while the rest are low.

A clock period of 0.1 ms ended up becoming problematic, as the microprocessor was unable to sample and convert in the DTC as well as switch the I/O pins fast enough to produce a frequency of 50 Hz, rendering the motors unusable.

The final clock period is 0.5 ms, a balance between sampling speed and the ability of the MSP430 to produce a PWM of 50 Hz. This clock period corresponds to a PWM period of 40 clock cycles. While this is still a relatively slow speed for playing Piano Tiles and limits the available options for PWM duty cycles (2-5 periods corresponding to only 4 stylus angles), it allows for a relatively quick response time between photoresistor readings and duty cycle setting.

Hardware:

After compiling and fine-tuning the software for this project, a few issues arose with component assembly and constraint. One of the first issues to tackle was the wire lengths on the stock servo motors used as well as the wire lengths connecting the photoresistors. The three-wire ribbon attached to the motors was fairly short and made it difficult to position all of the motors around the iPad without the board being pulled from multiple directions. To tackle this, extension cords were soldered together with each wire shrink tubed to avoid shorting. These served as a critical component to our functional final assembly. An image of one end of one of these extension cords is shown below in Figure 5. Similar soldering was done to extend the wires connecting to the photoresistors.

Figure 5: Servo motor extension cord

Another pain point was the constraint of the motors and photoresistors around the iPad itself. The motors had to be held rigidly in place against the reaction forces caused by the styluses tapping the screen with enough force to register touch. To combat this, the aforementioned PLA 3D printed casing was designed with 8 holes around each motor's location for zip ties to be strapped around the motors in multiple key places. For the photoresistors, the acrylic piece shown resting on top of the iPad screen was designed with four holes to place the photoresistors into. Hot glue was applied on top of the photoresistors to hold them down against any pulling forces from the wires. These custom components can be seen serving their respective functions below, in a video of the Tile Tapper in action.

Figure 6: The Tile Tapper during testing

Conclusion

In working on this project, Team M&P430 explored how the MSP430 can be applied to a wide range of projects, from hobby electronics to real-world technology. This project pushed the processor to its limit, balancing processing power and speed to accomplish the tile-tapping goal it was designed to achieve.

Schematics

Code

ME461_project_motorctrl.c

/******************************************************************************
MSP430F2272 Project Creator 4.0

ME 461 - S. R. Platt
Fall 2010

Updated for CCSv4.2 Rick Rekoske 8/10/2011

Written by: Steve Keres
College of Engineering Control Systems Lab
University of Illinois at Urbana-Champaign
*******************************************************************************/

#include "msp430x22x2.h"
#include "UART.h"

// global variables:

char newprint = 0;
unsigned int timecnt = 0;
unsigned int fastcnt = 0;
unsigned int fastcnt2 = 0;
int freq = 100;
int photoresist[4] = {0,0,0,0}; //two element integer array for sampled DTC channels
long A1_mv=0,A0_mv=0,A2_mv=0,A3_mv; // stores V reading from A1, A0
char P2_sw = 0;
unsigned int counter = 0;
unsigned int dutycounter = 0;

// motor selection variables
int A0_dutylimit = 0; // PWM counter for motor 1
int A1_dutylimit = 0; 
int A2_dutylimit = 0; 
int A3_dutylimit = 0; 

// motor selection and duty cycle
int A0_motorstate = 20; // Number of cycles motor 1 will stay high for
int A1_motorstate = 20; 
int A2_motorstate = 20; 
int A3_motorstate = 20; 

// color thresholds
int A0_white = 900; // White threshold; Reading above this keeps the pen up
int A0_black = 500; // Black threshold; Reading below this keeps the pen down
int A1_white = 900;
int A1_black = 700;
int A2_white = 2100;
int A2_black = 1950;
int A3_white = 1100;
int A3_black = 500;

void main(void) {

    WDTCTL = WDTPW + WDTHOLD; // Stop WDT

    if (CALBC1_16MHZ ==0xFF || CALDCO_16MHZ == 0xFF) while(1);

    DCOCTL  = CALDCO_16MHZ; // Set uC to run at approximately 16 Mhz
    BCSCTL1 = CALBC1_16MHZ;

    //P1IN          Port 1 register used to read Port 1 pins setup as Inputs
    P1SEL &= ~0xFF; // Set all Port 1 pins to Port I/O function
    P1REN &= ~0xFF; // Disable internal resistor for all Port 1 pins
    P1DIR |= 0xFF;   // Set all Port 1 pins to outputs
    P1OUT &= ~0xFF; // Initially set all Port 1 pins set as Outputs to zero

    // Timer A Config
    TACCTL0 = CCIE;              // Enable Timer A interrupt
    TACCR0  = 8000;             // period = 0.5ms
    TACTL   = TASSEL_2 + MC_1;   // source SMCLK, up mode

    P4SEL &= ~0x1E; // Sets P4.1 to TB1
    P4DIR |= 0x1E; // Sets P4.1 to TB1

    ADC10CTL0 |= SREF_0 + ADC10ON + ADC10IE + MSC; // Period = 51.2 us - Sets reference to GND and 3.3V, turns on ADC10, enables ADC10 interrupt
    ADC10CTL1 |= INCH_3 + CONSEQ_1 + ADC10SSEL_0 + SHS_0; // Uses function generator as sampling channel and clock source to ADC10OSC, sets input channel to A3
    ADC10AE0 |= 0x0F; // Enables channels we want to sample (A0,A1,A2,A3 = 1111 = hex 0F)
    ADC10DTC1 |= 0x04; // number of channels we want to sample
    ADC10SA = (int)&photoresist[0];

    Init_UART(115200, 1);   // Initialize UART for 9600 baud serial communication

    _BIS_SR(GIE);       // Enable global interrupt

    while(1) {

        if(newmsg) {
            //my_scanf(rxbuff,&var1,&var2,&var3,&var4);
            newmsg = 0;
        }

        if (newprint)  {
            P1OUT ^= 0x1; // Blink LED
            UART_printf("%d %d %d %d\n\r",(int)A0_mv, (int)A1_mv, (int)A2_mv, (int)A3_mv); //  %d int, %ld long, %c char, %x hex form, %.3f float 3 decimal place, %s null terminated character array
            // UART_send(1,(float)timecnt);

            timecnt++;  // Just incrementing this integer for default print out.
            newprint = 0;
        }

    }
}


// Timer A0 interrupt service routine
#pragma vector=TIMERA0_VECTOR
__interrupt void Timer_A (void)
{
    fastcnt++; // Keep track of time for main while loop.
    if (fastcnt == 50) {
        fastcnt = 0;
        newprint = 1;  // flag main while loop that .5 seconds have gone by.
    }

    ADC10CTL0 |= ENC + ADC10SC; // Enables ADC10 and starts conversion once every ms

    // Put your Timer_A code here:

    // MOTOR YEAH

    if (counter == 0) { // starts counting from 0, runs one time

        P4OUT |= 0x1E; // pulls all motors high
        A0_dutylimit = A0_motorstate; // sets duty cycle based on photoresistor
        A1_dutylimit = A1_motorstate;
        A2_dutylimit = A2_motorstate;
        A3_dutylimit = A3_motorstate;

        dutycounter = 0; // resets duty counter
    }

    if (dutycounter == A0_dutylimit) { // has motor 1 hit duty cycle limit? (X/200)
        P4OUT &= ~0x02; // if yea, turn off
    }

    if (dutycounter == A1_dutylimit) {
        P4OUT &= ~0x04;
    }

    if (dutycounter == A2_dutylimit) {
        P4OUT &= ~0x08;
    }

    if (dutycounter == A3_dutylimit) {
        P4OUT &= ~0x10;
    }

    counter++; // increments counter every loop (once every 0.5 ms)
    dutycounter++; // increments duty cycle counter every loop

    if (counter >= 40) { // if counter hits 40, aka 20ms has passed
        counter = 0;  //  reset counter
    }
}

// ADC 10 ISR - Called when a sequence of conversions (A7-A0) have completed
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void) {
    A3_mv = (photoresist[0]*3300L)/1023; // converts ADC10 memory to mV
    A2_mv = (photoresist[1]*3300L)/1023; // converts ADC10 memory to mV
    A1_mv = (photoresist[2]*3300L)/1023; // converts ADC10 memory to mV
    A0_mv = (photoresist[3]*3300L)/1023; // converts ADC10 memory to mV

    if (A0_mv < A0_black) { // if reading black color
        A0_motorstate = 2;  // hold pin high for 2/40 cycles = 5% duty cycle
    }

    if (A0_mv > A0_white) { // if reading white color
        A0_motorstate = 3;  // hold pin high for 3/40 cycles = 7.5% duty cycle
    }

    if (A1_mv < A1_black) {
        A1_motorstate = 3;
    }

    if (A1_mv > A1_white) {
        A1_motorstate = 2;
    }

    if (A2_mv < A2_black) {
        A2_motorstate = 2;
    }

    if (A2_mv > A2_white) {
        A2_motorstate = 3;
    }

    if (A3_mv < A3_black) {
        A3_motorstate = 3;
    }

    if (A3_mv > A3_white) {
        A3_motorstate = 2;
    }

    ADC10SA = (int)&photoresist[0];
}



// USCI Transmit ISR - Called when TXBUF is empty (ready to accept another character)
#pragma vector=USCIAB0TX_VECTOR
__interrupt void USCI0TX_ISR(void) {
  
    if((IFG2&UCA0TXIFG) && (IE2&UCA0TXIE)) { // USCI_A0 requested TX interrupt
        if(printf_flag) {
            if (currentindex == txcount) {
                senddone = 1;
                printf_flag = 0;
                IFG2 &= ~UCA0TXIFG;
            } else {
            UCA0TXBUF = printbuff[currentindex];
            currentindex++;
            }
        } else if(UART_flag) {
            if(!donesending) {
                UCA0TXBUF = txbuff[txindex];
                if(txbuff[txindex] == 255) {
                    donesending = 1;
                    txindex = 0;
                } else {
                    txindex++;
                }
            }
        }

        IFG2 &= ~UCA0TXIFG;
    }

    if((IFG2&UCB0TXIFG) && (IE2&UCB0TXIE)) { // USCI_B0 requested TX interrupt (UCB0TXBUF is empty)

        IFG2 &= ~UCB0TXIFG;   // clear IFG
    }
}


// USCI Receive ISR - Called when shift register has been transferred to RXBUF
// Indicates completion of TX/RX operation
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void) {
  
    if((IFG2&UCA0RXIFG) && (IE2&UCA0RXIE)) { // USCI_A0 requested RX interrupt (UCA0RXBUF is full)

        if(!started) {  // Haven't started a message yet
            if(UCA0RXBUF == 253) {
                started = 1;
                newmsg = 0;
            }
        } else { // In process of receiving a message
            if((UCA0RXBUF != 255) && (msgindex < (MAX_NUM_FLOATS*5))) {
                rxbuff[msgindex] = UCA0RXBUF;

                msgindex++;
            } else { // Stop char received or too much data received
                if(UCA0RXBUF == 255) { // Message completed
                    newmsg = 1;
                    rxbuff[msgindex] = 255; // "Null"-terminate the array
                }
                started = 0;
                msgindex = 0;
            }
        }
        IFG2 &= ~UCA0RXIFG;
    }

    if((IFG2&UCB0RXIFG) && (IE2&UCB0RXIE)) { // USCI_B0 requested RX interrupt (UCB0RXBUF is full)

        IFG2 &= ~UCB0RXIFG; // clear IFG
    }
  
}

Credits

Megin Budacki

1 project • 1 follower

Peyton Huene

1 project • 1 follower

The Tile Tapper