![]() Meanwhile, since we access these two variables frequently. The buffer length is 256 bytes and the pointers are also 8-bit - just let it overflow to zero when it exceeds 255, then we don't need to do extra compare operations. All these four buffers share the same "Head" and "Tail" pointer. In order to implement the methodology above, 4 independent buffers are created based on the data structure of 16-bit Wave File. ![]() To guarantee the audio quality, the code in sampling ISR must be as short as possible as is shown above. Note that if you need to write SD card efficiently, than you should use FatFs (also developed by ChaN) NOT Petit-FatFs.Īudio Data Process and Software Utilizationīasically, audio data process can be divided into "Retrieving" and "Consuming" process. Then we can access SD card following file system standard. This light-weight / open-source file system is developed by ChaN, which support FAT12/16/32. Note that, for MISO signal, 3.3V is acceptable by AVR, so it does not need extra resistor divider. To interact with SD card correctly, resistor dividers (3.3K and 1.8K) are used to guarantee AVR's SPI signal level would never exceed 3.3V. To ensure system stability, ATmega1284p is powered by 5V while SD card is powered by 3.3V with a cheap, linear regulator such as LT1117-3V3. Even though ATmega1284p can also work at 3.3V, it may not be able to work at 16MHz ("Atmel-8272-8-bit-AVR-microcontroller-ATmega164A_PA-324A_PA-644A_PA-1284_P_datasheet", pp 336, Figure 28-1). SD card can only accept 3.3V operating voltage level. You can check 16-Bit DAC / PWM on Arduino UNO - Ec-Projects for more information. It is obvious that if the resistor accuracy can be up to 0.3%, then it is able to achieve full 16-bit resolution. Assume resistor accuracy (tolerance) is 1%, then the actual output should be: 0.0191V < V < 0.0199V. In this way, when MSB PWM outputs 0V while LSB PWM outputs 5V, we can calculate the minimum resolution is about 0.01942V. The larger resistor is connected to LSB PWM output channel while the smaller resistor is connected to MSB PWM channel. In this project, the PWM Combination circuit is composed of two resitors: 1M and 3.9K. ![]() Then we can make this second analog signal represent lower order bits via selecting correct summing ratio. However, we can simply create another analog signal via another PWM output channel. Single PWM output can use one output pin to generate analog signals with 8-bit resolution (as we learned in LAB2). PROJECT VIDEO HARDWARE How to combine two 8-bit PWM output into one 16-bit DAC?
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