• Digital Voice Recorder
• 8-bit Sound Recording
• 8 kHz Sampling Rate
• Sound Frequency up to 4000 Hz
• Maximum Recording Time 4 1/4 Minutes
• Very Small Board Size
• Less than 700 Bytes of Code
This application note describes how to record, store and play back sound using any AVR microcontroller with A/D converter, the AT45DB161B DataFlash memory and a few extra components.
This application note shows in detail the usage of the A/D Converter for sound recording, the Serial Peripheral Interface – SPI – for accessing the external DataFlash memory and the Pulse Width Modulation – PWM – for playback. Typical applications that would require one or more of these blocks are temperature loggers, telephone answering machines, or digital voice recorders.
The AT45DB161B DataFlash is a 2.7 volt only, Serial-interface Flash memory. Its 16 Mbit of memory are organized as 4096 pages of 528 bytes each. In addition to its main memory, the DataFlash contains two SRAM data buffers of 528 bytes each. The buffers allow a virtually continuous data stream to be written to the DataFlash.
The AT45DB161B uses an SPI serial interface to sequentially access its data. This interface facilitates hardware layout, increases system reliability, minimizes switching noise, and reduces package size and active pin count. Typical applications are image storage, data storage and digital voice storage. The DataFlash operates at SPI clock frequencies up to 20 MHz with a typical active read current consumption of 4 mA. It operates from a single voltage power supply (from 2.7V to 3.6V) for both the write and read operations.
Its serial interface is compatible to the Serial Peripheral Interface – SPI – Modes 0 and 3, thus it can easily be interfaced to the AVR microcontroller.
In this application note the AVR AT90S8535 is used to take analog samples from a microphone and convert them to digital values. Its built-in SPI controls data transfers to and from the DataFlash. The PWM feature of the AVR is used for playback. The code size is very small, the application will therefore also fit into smaller AVR devices.
Source: Atmel Corporation