1. MSP430 Semester Project ECE 300 Circuits

2. 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

3. 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

4. Max4238 Ultra-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

5. Typical Circuit

6. 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

7. Plot of Calibration Data

8. 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

9. 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 " */

10. 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

11. Questions