MSP430 Semester Project

ECE 300 Circuits

MSP 430

16 Bit RISC Micro-controller Low Power 12 Bit A/D Converter 6 Digital I/O ports (8 lines per port) 2 UARTs for Serial Communication

Load Cell Weight Pad

Aluminum Load cell with embedded strain gauge

The strain gauge requires an “excitation voltage”

The output voltage needs to be amplified

Max4238Ultra-Low Offset/Drift, Low-Noise, Precision SOT23 Amplifiers

Can Operate from a single 2.7V – 5.5V Supply Rail to Rail Outputs Near-zero DC offset and drift

Typical Circuit

12 Bit - ADC

Op-amp amplifying by a factor of ~ 115 Strain gauge outputs 1.992mV /V of excitation

at full load 115 x 3.3 X .001992V = 0.756 V at full load Use Analogue Reference of 1.5 V Only using about half the resolution of the ADC Can only resolve down to about 0.012 Kg

Plot of Calibration Data

y = 1.165871754E+00x - 3.863419569E-01

R2 = 9.999543453E-01

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5

Series1

Linear (Series1)d

Increase the Update Rate

// set up Basic Timer IE2 |= BTIE; // Enable BT interrupt //BTCTL = BT_ADLY_2000 | BT_fLCD_DIV256; // Original Code BTCTL = BT_ADLY_32 | BT_fLCD_DIV256; // 32ms Interrupt

// set up ADC ADC12IE |= 0x0040; // Enable ADC6 interrupt //ADC12CTL0 = ADC12ON + REF2_5V + REFON; // Original ADC12CTL0 = ADC12ON + REFON; // Aref = 1.5V, Aref on ADC12CTL1 = CSTARTADD_6 + ADC12SSEL_1 + SHP; ADC12MCTL6 = SREF_1 + INCH_6; ADC12CTL0 |= ENC ; //Enables ADC

Defined in MSP430.h

/* with assumed vlues of fACLK=32KHz, fMCLK=1MHz */ /* fBT=fACLK is thought for longer interval times */ #define BT_ADLY_0_064 (0x00) /* 0.064ms interval (default) */ #define BT_ADLY_0_125 (BTIP0) /* 0.125ms " */ #define BT_ADLY_0_25 (BTIP1) /* 0.25ms " */ #define BT_ADLY_0_5 (BTIP1+BTIP0) /* 0.5ms " */ #define BT_ADLY_1 (BTIP2) /* 1ms " */ #define BT_ADLY_2 (BTIP2+BTIP0) /* 2ms " */ #define BT_ADLY_4 (BTIP2+BTIP1) /* 4ms " */ #define BT_ADLY_8 (BTIP2+BTIP1+BTIP0) /* 8ms " */ #define BT_ADLY_16 (BTDIV) /* 16ms " */ #define BT_ADLY_32 (BTDIV+BTIP0) /* 32ms " */ #define BT_ADLY_64 (BTDIV+BTIP1) /* 64ms " */ #define BT_ADLY_125 (BTDIV+BTIP1+BTIP0) /* 125ms " */ #define BT_ADLY_250 (BTDIV+BTIP2) /* 250ms " */ #define BT_ADLY_500 (BTDIV+BTIP2+BTIP0) /* 500ms " */ #define BT_ADLY_1000 (BTDIV+BTIP2+BTIP1) /* 1000ms " */ #define BT_ADLY_2000 (BTDIV+BTIP2+BTIP1+BTIP0) /* 2000ms " */

Features to Add

Increase excitation voltage Tare Button Conversion from Kg to Lbs Calibration Mode Use SPI to link Multiple Weight pads to one

MSP430

Questions