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Weekend-project: Autoranging microvoltmeter based on the MSP430FR4133 launchpad. ADC used: MIcrochip MCP3422, an 18bit, 3.75 sample/second Sigma Delta with 2 differential inputs. I2C interface This nice little chip contains a programmable amplifier (x2,x4,x8) and a not-too-bad internal reference of 2.048V. Max input range is +/-2.048V, resolution (8x amplified) is 2uV. Hand-etched a single layer PCB which goes on top of Launchpad. Type K cable in hot water: 2.93mV, 73Kelvin temp difference to ambient compare with my Fluke 289, 0.06% (datasheet says 0.05% typical, 0.35% max) Not too shabby for a chip that costs 3 bucks. Current consumption: on average <40uA, the whole setup would run 5000hours from a CR2032 The ADC does 1 sample/second and sleeps the rest of the time, the MSP430 does what it likes the most: sleep in LPM3 Code is not a big deal, quick hack based on the FR4133 examples, for the LCD and for the I2C interface //microvolt meter with MCP3422 and MSP430FR413 //****************************************************************************** #include <msp430.h> #define LCDMEMW ((int*)LCDMEM) #define pos1 4 // Digit A1 - L4 #define pos2 6 // Digit A2 - L6 #define pos3 8 // Digit A3 - L8 #define pos4 10 // Digit A4 - L10 #define pos5 2 // Digit A5 - L2 #define pos6 18 // Digit A6 - L18 const char digit[10] ={ 0xFC, // "0" 0x60, // "1" 0xDB, // "2" 0xF3, // "3" 0x67, // "4" 0xB7, // "5" 0xBF, // "6" 0xE0, // "7" 0xFF, // "8" 0xF7 // "9" }; volatile long voltage; unsigned long dvoltage; unsigned char TXByteCtr; unsigned char TXData; unsigned char newgain,gain; void Clear_LCD(){ int i; for(i=5;i;i--) LCDMEMW[i]=0; LCDMEMW[9]=0; } int main( void ) { WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer P1OUT = 0x00;P2OUT = 0x00;P3OUT = 0x00;P4OUT = 0x00; P5OUT = 0x00;P6OUT = 0x00;P7OUT = 0x00;P8OUT = 0x00; P1DIR = 0xFF;P2DIR = 0xFF;P3DIR = 0xFF;P4DIR = 0xFF; P5DIR = 0xFF;P6DIR = 0xFF;P7DIR = 0xFF;P8DIR = 0xFF; P5SEL0 |= BIT2 | BIT3; // I2C pins // Configure XT1 oscillator P4SEL0 |= BIT1 | BIT2; // P4.2~P4.1: crystal pins do { CSCTL7 &= ~(XT1OFFG | DCOFFG); // Clear XT1 and DCO fault flag SFRIFG1 &= ~OFIFG; } while (SFRIFG1 & OFIFG); // Test oscillator fault flag // Disable the GPIO power-on default high-impedance mode // to activate previously configured port settings PM5CTL0 &= ~LOCKLPM5; CSCTL4 = SELMS__DCOCLKDIV + SELA__XT1CLK; // MCLK=SMCLK=DCO; ACLK=XT1 // Configure RTC RTCCTL |= RTCSS__XT1CLK | RTCIE; // Initialize RTC to use XT1 and enable RTC interrupt RTCMOD = 16384; // Set RTC modulo to 16384 to trigger interrupt twice a second // Configure LCD pins SYSCFG2 |= LCDPCTL; // R13/R23/R33/LCDCAP0/LCDCAP1 pins selected LCDPCTL0 = 0xFFFF; LCDPCTL1 = 0x07FF; LCDPCTL2 = 0x00F0; // L0~L26 & L36~L39 pins selected LCDCTL0 = LCDSSEL_0 | LCDDIV_7; // flcd ref freq is xtclk // LCD Operation - Mode 3, internal 3.08v, charge pump 256Hz LCDVCTL = LCDCPEN | LCDREFEN | VLCD_5 | (LCDCPFSEL0 | LCDCPFSEL1 | LCDCPFSEL2 | LCDCPFSEL3); LCDMEMCTL |= LCDCLRM; // Clear LCD memory LCDCSSEL0 = 0x000F; // Configure COMs and SEGs LCDCSSEL1 = 0x0000; // L0, L1, L2, L3: COM pins LCDCSSEL2 = 0x0000; LCDM0 = 0x21; // L0 = COM0, L1 = COM1 LCDM1 = 0x84; // L2 = COM2, L3 = COM3 LCDCTL0 |= LCD4MUX | LCDON; // Turn on LCD, 4-mux selected (LCD4MUX also includes LCDSON) Clear_LCD(); // Configure USCI_B0 for I2C mode UCB0CTLW0 |= UCSWRST; // Software reset enabled UCB0CTLW0 |= UCMODE_3 | UCMST | UCSYNC; // I2C mode, Master mode, sync UCB0CTLW1 |= UCASTP_2; // Automatic stop generated // after UCB0TBCNT is reached UCB0BRW = 0x0008; // baudrate = SMCLK / 8 UCB0I2CSA = 0x0068; // Slave address UCB0CTL1 &= ~UCSWRST; UCB0IE |= UCRXIE | UCNACKIE | UCBCNTIE | UCTXIE0; while(1){ // P1OUT |= BIT0; TXByteCtr = 1; // Load TX byte counter TXData = 0x8C+gain; while (UCB0CTLW0 & UCTXSTP); // Ensure stop condition got sent UCB0CTLW0 |= UCTR | UCTXSTT; // I2C TX, start condition // P1OUT &= ~BIT0; __bis_SR_register(LPM3_bits | GIE); // timer will wake me up // P1OUT |= BIT0; UCB0TBCNT = 0x0003; // 3 bytes to be received voltage=0; UCB0CTLW0 &= ~UCTR; while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent UCB0CTL1 |= UCTXSTT; // I2C start condition __bis_SR_register(LPM3_bits | GIE); // I2C irq will wake me up voltage<<=8; // shift to left corner to do the sign correctly voltage/=32; // calibration is done here: 2048 in an ideal world if ((voltage<400000)&&(voltage>(-400000))){ // autoranging, downshift if (newgain<3) newgain++; } if ((voltage>1000000)||(voltage<-1000000)){ // autoranging, upshift if (newgain) newgain--; } voltage>>=gain; gain=newgain; if ((voltage<500000)&&(voltage>-500000)){ voltage*=10; //low range LCDMEM[11]&=~1; //adjust decimal point LCDMEM[9]|=1; } else{ //high range LCDMEM[9]&=~1; //adjust decimal point LCDMEM[11]|=1; } voltage*=25; voltage/=128; if (voltage<0) {dvoltage=-voltage; LCDMEM[5]|=4 ;} //negative else {dvoltage= voltage; LCDMEM[5]&=~4;} //positive LCDMEM[pos1] = digit[(dvoltage / 100000)%10]; LCDMEM[pos2] = digit[(dvoltage / 10000)%10]; LCDMEM[pos3] = digit[(dvoltage / 1000)%10]; LCDMEM[pos4] = digit[(dvoltage / 100)%10]; LCDMEM[pos5] = digit[(dvoltage / 10)%10]; LCDMEM[pos6] = digit[dvoltage % 10]; // P1OUT &= ~BIT0; __bis_SR_register(LPM3_bits | GIE); // timer will wake me up } } #pragma vector = RTC_VECTOR __interrupt void RTC_ISR(void){ switch(__even_in_range(RTCIV, RTCIV_RTCIF)){ case RTCIV_NONE: break; // No interrupt case RTCIV_RTCIF: // RTC Overflow __bic_SR_register_on_exit(LPM3_bits); break; default: break; } } #pragma vector = USCI_B0_VECTOR __interrupt void USCIB0_ISR(void){ switch(__even_in_range(UCB0IV, USCI_I2C_UCBIT9IFG)){ case USCI_NONE: break; // Vector 0: No interrupts case USCI_I2C_UCALIFG: break; // Vector 2: ALIFG case USCI_I2C_UCNACKIFG: // Vector 4: NACKIFG UCB0CTL1 |= UCTXSTT; // I2C start condition break; case USCI_I2C_UCSTTIFG: break; // Vector 6: STTIFG case USCI_I2C_UCSTPIFG: break; // Vector 8: STPIFG case USCI_I2C_UCRXIFG3: break; // Vector 10: RXIFG3 case USCI_I2C_UCTXIFG3: break; // Vector 14: TXIFG3 case USCI_I2C_UCRXIFG2: break; // Vector 16: RXIFG2 case USCI_I2C_UCTXIFG2: break; // Vector 18: TXIFG2 case USCI_I2C_UCRXIFG1: break; // Vector 20: RXIFG1 case USCI_I2C_UCTXIFG1: break; // Vector 22: TXIFG1 case USCI_I2C_UCRXIFG0: // Vector 24: RXIFG0 voltage=(voltage<<8)+UCB0RXBUF; break; case USCI_I2C_UCTXIFG0: // Vector 26: TXIFG0 if (TXByteCtr){ // Check TX byte counter UCB0TXBUF = TXData; // Load TX buffer TXByteCtr--; // Decrement TX byte counter } else{ UCB0CTLW0 |= UCTXSTP; // I2C stop condition UCB0IFG &= ~UCTXIFG; // Clear USCI_B0 TX int flag } break; case USCI_I2C_UCBCNTIFG: // Vector 28: BCNTIFG __bic_SR_register_on_exit(LPM3_bits); break; case USCI_I2C_UCCLTOIFG: break; // Vector 30: clock low timeout case USCI_I2C_UCBIT9IFG: break; // Vector 32: 9th bit default: break; } }