Laboratory signal acquisition: lab1 - sar adc10 conversion  (Page 9/2)

Laboratory signal acquisition: lab1 - sar adc10 conversion

Introduction

This laboratory gives examples of the uses of the ADC types available in the hardware development kits. A different laboratory is developed for each kit, taking into account that both the ADC10 and the SD16_A laboratories implement a temperature data logger. The ADC12 laboratory also uses operational amplifiers to perform the analogue signal conditioning.

Overview

This laboratory ( Lab1_ADC.c ) implements a temperature data logger using the hardware kit’s integrated temperature sensor. The device is configured to perform an acquisition each minute for one hour. Each temperature’s (ºC) value is transferred to flash info memory segment B and C. When the microcontroller is not performing any task, it enters into low power mode.

Resources

The ADC10 module uses V _REF+ = 1.5 V as the reference voltage.

It is necessary to configure the ADC10 to use the integrated temperature sensor (A10) as an input. Timer_A generates an interrupt once every second that starts conversion in the ADC10. At the end of a conversion, an interrupt is requested by the converter and the temperature value is written to flash memory.

The voltage value is converted into temperature following the equation provided in ADC10 section of the MSP430 User’s Guide<slau144e.pdf>. After transferring the value to the flash memory, the system returns to low power mode LPM3.

The resources used by the application are:

- ADC10;

- Timer_A;

- Ports I/O;

- Interrupts;

- Low power mode.

Software application organization

The application starts by stopping the Watchdog Timer.

The system checks for calibration constants on info memory segment A. The CPU execution will be trapped if it does not find this information.

Digitally controller oscillator (DCO) is set to 1 MHz, providing clock source for MCLK and SMCLK, while the Basic Clock System+ is configured to set ACLK to 1.5 kHz.

Controller’s flash timing is obtained from MCLK divided by three to comply with the device specifications.

Port P1.0 is configured as an output and will blink the once LED every second.

The ADC10 is configured to use the input channel corresponding to the on-chip temperature sensor (channel A10). The configuration includes the activation of the internal reference voltage V _REF+ = 1.5 V and the selection of ADC10OSC as clock signal. The converter is configured to perform a single-channel single-conversion. At the end of conversion, an interrupt is requested.

The Timer_A is configured to generate an interrupt once every second. ACLK/8 is selected as the clock signal using the VLOCLK as clock source and will count until the TACCR0 value is reached (in up mode). The system then enters into low power mode and waits for an interrupt.

Flash memory pointers and interrupt counters are initialized. The Timer_A ISR increments the variable counter and when this variable reaches the value 60 (1 minute), the software start of conversion is requested. At the end of this ISR, the system returns to low power mode.