Main Features & Specifications
• Uses an MMC/SD/SDHC card to store audio files
• Stores mono recordings as Microsoft WAV files at 16kHz sampling rate
• Plays back Microsoft WAV files at up to 44.1kHz sampling rate
• Uses FAT/FAT32 file system (transfer files to any PC operating system)
• Has mono microphone and line inputs for recording
• Stereo socket for line output or headphone use
• 2-line LCD to display file names, show volume and other settings
• Can be controlled using on-board switches or any RC5 universal remote control
• Unit can learn remote control codes
• Signal-to-noise ratio: -70dB unweighted (22Hz to 22kHz) with respect 1.6V RMS
• THD+N: 0.7% at 1kHz
A universal IR remote is used to control the Digital Speech Recorder or you can use the on-board buttons. Recordings can be made direct to the memory card via a mic or line input or you can copy audio files onto the card from a PC.
In May 2005 and December 2007 we published two very popular solid-state voice recorder projects. The 2007 design was an improved version of the original project, employing the same voice recorder chip. These allowed you to record a number of short messages (up to about one minute of speech) and play them back at the touch of a button. The messages were stored in “analog EEPROM” cells in an analog 8-bit format.
This project takes the message recorder concept to a whole new level and employs a common SD memory card or MMC (multimedia card) for message storage. Depending on the size of the card, you can store and play back many hours of audio. We’ve also added infrared remote control and it can be used to play back any WAV file that you have downloaded or recorded on your PC.
We are presenting this project in a very simple module format; it is just a PC board with an SD card socket, a 2-line LCD panel and eight pushbutton switches to select the audio files and other features. If you want to build the unit into a case, you can take the LCD panel off the board and separately mount it and the same goes for the switches and sockets.
Compatible memory cards
The compatible cards to use with this project are MMC (MultiMedia Card), SD (Secure Digital) and SDHC (Secure Digital High Capacity) cards. SD cards come in capacities up to 2GB. Beyond that, you will find SDHC cards with capacities from 4GB to 32GB. The current version of the standard does not specify cards with capacities higher than 32GB, although these will become common in the future.
This project will work with most presently available cards. SD cards in particular have dropped in price dramatically and you can now pick up a 1GB SD card for less than $10.