Description: The personal website of Scott W. Harden
circuit microcontroller This project uses a microcontroller’s PWM output to drive a speaker and play audio stored in a SPI flash chip. This article combines what was learned in my two previous articles: play audio with a microcontroller and use a FT232H to program a SPI flash chip which go into more detail about the circuitry and code behind each of these major steps. By encoding audio at 8-bit resolution with an 8 kHz sample rate, 32 Mb (4 MB) of memory is sufficient to store approximately 8 minutes of raw
Audio levels are stored in the SPI flash memory, so by reading each address and setting the PWM level to that value at a rate of 8 kHz, the sounds stored in flash memory can be played back in real time. Here are the important parts of the Arduino code I used to achieve continuous audio playback, and the full source code can be reviewed in audio.ino on GitHub.
The delay between each cycle of the main loop (88 µs) was determined experimentally to achieve approximately 8 kHz playback. Ideally another timer’s interrupt could manage playback, but the Arduino’s primary timer is occupied with systems tasks (like timing) and the secondary timer is used for PWM (to generate the analog audio output waveform), so this was the simplest option. An alternative approach could probably be to slow down the PWM timer’s period and use its overflow interrupt and a counter to manage
Amateur Radio Station: KC4ZVW
Amateur Radio Station: KC4ZVW
WA0UWH - Electronics & HAM Radio Blog
YO7FWS
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Hack Ability
Amateur Radio Club at Cornell
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