MSP430 LCD Interfacing: Displaying ADC Readings

By Prabeesh Keezhathra

- 6 minutes read - 1093 words

Interfacing a 16x2 LCD with an MSP430 gives you cheap, on-board output for embedded projects. This post wires one up to a LaunchPad, samples a potentiometer with the ADC, and writes the measured voltage to the display.

Project Overview

Our system reads analog voltage from a potentiometer connected to the MSP430’s ADC channel and displays the digital value on an LCD screen in real-time. This fundamental pattern applies to countless sensor monitoring applications in embedded systems.

System Components

  • MSP430 LaunchPad (main microcontroller board)
  • 16x2 LCD display for showing readings
  • Potentiometer as a variable voltage source for ADC input
  • External 5V power supply for the LCD

Understanding MSP430 ADC Fundamentals

The MSP430’s 10-bit ADC provides precise analog-to-digital conversion essential for sensor interfacing. Here’s how the conversion process works:

ADC Resolution and Range

The MSP430 LaunchPad operates at 3.6V, giving us a working voltage range of 0V to 3.6V. The 10-bit ADC resolution means:

Minimum Input (0V):

Binary: 0000000000
Decimal: 0

Maximum Input (3.6V):

Binary: 1111111111  
Decimal: 1023

This gives us a resolution of 3.6V ÷ 1023 = 3.52mV per step, providing excellent precision for most sensing applications.

Voltage Calculation Formula

To convert ADC readings back to voltage:

Voltage = (ADC_Value × 3.6V) ÷ 1023

Circuit Design and Connections

Power Supply Considerations

The MSP430 operates at 3.6V while standard LCD displays require 5V for reliable operation. This mixed-voltage design requires careful consideration:

  • Potentiometer supply: powered from the MSP430’s 3.6V rail
  • LCD supply: powered from an external 5V source
  • Data lines: the MSP430’s 3.6V logic levels are compatible with 5V LCD inputs

Pin Configuration

The LCD uses a 4-bit interface to minimize pin usage while maintaining functionality:

1// LCD Pin Assignments
2#define LCM_PIN_RS BIT2  // P1.2 - Register Select
3#define LCM_PIN_EN BIT1  // P1.1 - Enable Signal  
4#define LCM_PIN_D7 BIT7  // P1.7 - Data Bit 7
5#define LCM_PIN_D6 BIT6  // P1.6 - Data Bit 6
6#define LCM_PIN_D5 BIT5  // P1.5 - Data Bit 5
7#define LCM_PIN_D4 BIT4  // P1.4 - Data Bit 4

Potentiometer connection: P1.0 (ADC Channel A0)

Code Implementation Breakdown

ADC Configuration

 1void adc_init()
 2{
 3    // Configure ADC: 10-bit resolution, internal reference
 4    ADC10CTL0 = ADC10ON | ADC10SHT_2 | SREF_0;
 5    
 6    // Select input channel A0, single-conversion mode
 7    ADC10CTL1 = INCH_0 | SHS_0 | ADC10DIV_0 | ADC10SSEL_0 | CONSEQ_0;
 8    
 9    // Enable analog input on P1.0
10    ADC10AE0 = BIT0;
11    
12    // Enable conversions
13    ADC10CTL0 |= ENC;
14}

Key Configuration Details:

  • ADC10SHT_2: Sets sample-and-hold time for accurate conversions
  • SREF_0: Uses VCC and VSS as voltage references
  • INCH_0: Selects input channel A0 (P1.0)

LCD Communication Protocol

The LCD uses a parallel interface with specific timing requirements:

 1void PulseLcm()
 2{
 3    // LCD Enable pulse sequence for data transfer
 4    LCM_OUT &= ~LCM_PIN_EN;  // Pull EN low
 5    __delay_cycles(200);      // Wait for setup time
 6    
 7    LCM_OUT |= LCM_PIN_EN;   // Pull EN high  
 8    __delay_cycles(200);      // Hold time
 9    
10    LCM_OUT &= ~LCM_PIN_EN;  // Pull EN low
11    __delay_cycles(200);      // Recovery time
12}

The LCD requires precise enable pulse timing for reliable data transfer.

Main Application Loop

 1void main(void)
 2{
 3    adc_init();
 4    int i, adc_value;
 5    char display_buffer[5];
 6    
 7    WDTCTL = WDTPW + WDTHOLD; // Disable watchdog timer
 8    InitializeLcm();
 9    
10    while(1)
11    {
12        // Start ADC conversion
13        start_conversion();
14        
15        // Wait for conversion completion
16        while(converting());
17        
18        // Read conversion result
19        adc_value = ADC10MEM;
20        
21        // Convert to ASCII string
22        itoa(adc_value, display_buffer, 10);
23        
24        // Update LCD display
25        ClearLcmScreen();
26        PrintStr(display_buffer);
27        
28        // Simple delay for display stability
29        for(i = 0; i < 5000; i++);
30    }
31}

Complete Implementation Code

Here’s the full implementation with comprehensive LCD and ADC handling:

  1#include <msp430.h>
  2
  3// LCD Pin Definitions
  4#define LCM_DIR P1DIR
  5#define LCM_OUT P1OUT
  6
  7#define LCM_PIN_RS BIT2 // P1.2
  8#define LCM_PIN_EN BIT1 // P1.1
  9#define LCM_PIN_D7 BIT7 // P1.7
 10#define LCM_PIN_D6 BIT6 // P1.6
 11#define LCM_PIN_D5 BIT5 // P1.5
 12#define LCM_PIN_D4 BIT4 // P1.4
 13#define LCM_PIN_MASK ((LCM_PIN_RS | LCM_PIN_EN | LCM_PIN_D7 | LCM_PIN_D6 | LCM_PIN_D5 | LCM_PIN_D4))
 14
 15#define FALSE 0
 16#define TRUE 1
 17
 18// ADC Functions
 19void adc_init()
 20{
 21    ADC10CTL0 = ADC10ON | ADC10SHT_2 | SREF_0;
 22    ADC10CTL1 = INCH_0 | SHS_0 | ADC10DIV_0 | ADC10SSEL_0 | CONSEQ_0;
 23    ADC10AE0 = BIT0;
 24    ADC10CTL0 |= ENC;
 25}
 26
 27void start_conversion()
 28{
 29    ADC10CTL0 |= ADC10SC;
 30}
 31
 32unsigned int converting()
 33{
 34    return ADC10CTL1 & ADC10BUSY;
 35}
 36
 37// LCD Functions
 38void PulseLcm()
 39{
 40    // pull EN bit low
 41    LCM_OUT &= ~LCM_PIN_EN;
 42    __delay_cycles(200);
 43    // pull EN bit high
 44    LCM_OUT |= LCM_PIN_EN;
 45    __delay_cycles(200);
 46    // pull EN bit low again
 47    LCM_OUT &= (~LCM_PIN_EN);
 48    __delay_cycles(200);
 49}
 50
 51void SendByte(char ByteToSend, int IsData)
 52{
 53    // clear out all pins
 54    LCM_OUT &= (~LCM_PIN_MASK);
 55    LCM_OUT |= (ByteToSend & 0xF0);
 56
 57    if (IsData == TRUE)
 58    {
 59        LCM_OUT |= LCM_PIN_RS;
 60    }
 61    else
 62    {
 63        LCM_OUT &= ~LCM_PIN_RS;
 64    }
 65
 66    PulseLcm();
 67    LCM_OUT &= (~LCM_PIN_MASK);
 68    LCM_OUT |= ((ByteToSend & 0x0F) << 4);
 69
 70    if (IsData == TRUE)
 71    {
 72        LCM_OUT |= LCM_PIN_RS;
 73    }
 74    else
 75    {
 76        LCM_OUT &= ~LCM_PIN_RS;
 77    }
 78
 79    PulseLcm();
 80}
 81
 82void LcmSetCursorPosition(char Row, char Col)
 83{
 84    char address;
 85    // construct address from (Row, Col) pair
 86
 87    if (Row == 0)
 88    {
 89        address = 0;
 90    }
 91    else
 92    {
 93        address = 0x40;
 94    }
 95
 96    address |= Col;
 97    SendByte(0x80 | address, FALSE);
 98}
 99
100void ClearLcmScreen()
101{
102    // Clear display, return home
103    SendByte(0x01, FALSE);
104    SendByte(0x02, FALSE);
105}
106
107void InitializeLcm(void)
108{
109    LCM_DIR |= LCM_PIN_MASK;
110    LCM_OUT &= ~(LCM_PIN_MASK);
111    __delay_cycles(100000);
112    LCM_OUT &= ~LCM_PIN_RS;
113    LCM_OUT &= ~LCM_PIN_EN;
114    LCM_OUT = 0x20;
115    PulseLcm();
116    SendByte(0x28, FALSE);
117    SendByte(0x0E, FALSE);
118    SendByte(0x06, FALSE);
119}
120
121void PrintStr(char *Text)
122{
123    char *c;
124    c = Text;
125
126    while ((c != 0) && (*c != 0))
127    {
128        SendByte(*c, TRUE);
129        c++;
130    }
131}
132
133void main(void)
134{
135    adc_init();
136    int i, a;
137    char b[5];
138    WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
139    InitializeLcm();
140
141    while(1)
142    {
143        start_conversion();
144        while(converting());
145        a = ADC10MEM;
146        itoa(a, b, 10); // integer to ASCII
147        ClearLcmScreen();
148        PrintStr(b);
149        for(i = 0; i < 5000; i++);
150    }
151}

Video Demonstration

Watch the complete project in action, demonstrating real-time ADC value updates as the potentiometer is adjusted.

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