MSP430 Semester Project

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
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

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

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Defined in MSP430.h

• / with assumed vlues of fACLK32KHz, fMCLK1MHz
  /
• / fBTfACLK 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 (BTIP1BTIP0)
  / 0.5ms " /
• define BT_ADLY_1 (BTIP2)
  / 1ms " /
• define BT_ADLY_2 (BTIP2BTIP0)
  / 2ms " /
• define BT_ADLY_4 (BTIP2BTIP1)
  / 4ms " /
• define BT_ADLY_8 (BTIP2BTIP1BTIP0)
  / 8ms " /
• define BT_ADLY_16 (BTDIV)
  / 16ms " /
• define BT_ADLY_32 (BTDIVBTIP0)
  / 32ms " /
• define BT_ADLY_64 (BTDIVBTIP1)
  / 64ms " /
• define BT_ADLY_125 (BTDIVBTIP1BTIP0)
  / 125ms " /
• define BT_ADLY_250 (BTDIVBTIP2)
  / 250ms " /
• define BT_ADLY_500 (BTDIVBTIP2BTIP0)
  / 500ms " /
• define BT_ADLY_1000 (BTDIVBTIP2BTIP1)
  / 1000ms " /
• define BT_ADLY_2000 (BTDIVBTIP2BTIP1BTI
  P0) / 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