voice record playback using MSP430F2013

>>how the PWM can be used instead of DAC.

Please see the following app note and code as a start:

http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slaa405a

 

Hi,

in addition you may want to have a look at this app note (http://focus.ti.com/mcu/docs/litabsmultiplefilelist.tsp?sectionId=96&tabId=1502&literatureNumber=slaa281b&docCategoryId=1&familyId=342) - SDcard interface to an MSP430.

Rgds
aBUGSworstnightmare

Krishna Thallapaka said:

I'm using an external SD card to store sound files.

The schematic is more or less straightforward. If both, MSP and SD card are running on 3.3V, just connect the SCLK and DATA_IN and DATA_OUT line of the SD card to the MSPs SPI lines and the CS pin to a GPIO pin. You can also use card detect an dmaybe write_protect too.

The mode to use treh SD card is the MMC serial mode (not available for SDHC cards) and provides fast and easy access to the 512 byte sectors on the card.

However, the initialisation isn't trivial and after you have initialized the card and can read the data sectors, you'll need support for the the high-level file system protocol to access the files and the data on the card.

For the low-level part there are some threads in this forum.

Krishna Thallapaka said:

I would be happy to know how the PWM can be used instead of DAC.

PWM is a fixed-frequency series of pulses with a certain high-to-low ratio (Duty Cycle). If you pass this signal through a low-pass filter, the resulting voltage is the average of the high and low times of the signal. So if the PWM signal has a 3V level and a 50% duty cycle, the result after the low pass would be 1.5V. For 10% duty cycle it would be 0.3V etc. Effectively it is a function of charging and discharging time of the capacitor in the low-pass. Keep in mind that there will be a remaining distortion that consists of the ratio of filter frequency and PWM frequency, steepness of the filter, quality of the capacitor and some other things. For higher quality, a more complex low-pass is required than ust a resistor and a capacitor.

About how to do PWM on the MSP is described in several other threads and in the appnotes already mentioned.