Integrated circuits ISD1012, ISD1016 and ISD1020 from chip maker ISD enable sounds to be recorded and played back simultaneously. The Final two digits in the type coding show the length of a sound message in seconds.
What is Solid State Audio Recorder?
Solid state recorder (SSR) is a device that records audio data using solid state technology. SSR records data in digital format in chips and this allows it to record as well as playback simultaneously.
The difference in recording and play back time is caused by the sampling frequency, which is highest (10.6 kHz) for the shorter time.
The circuits have a non-volatile memory that can store the recorded sound for not less than ten years without any supply voltage. The circuits also contain a microphone amplifier and an output amplifier.
Solid State Audio Recorder Circuit Diagram:
The drawing shows the simplest circuit for using one of these ICs; an electret microphone, a loudspeaker, three operating switches and a power supply.
Description of Audio Recorder Circuit Diagram:
S1 is the recording/playback switch for recording. It must be closed. Switch S2, when open, sets the IC to the power down mode. The larger part of the circuit is then switched off which reduces the current drain. Switching to power down also serves as a reset when, for instance, during recording an over flow (too long message) occurs. The IC indicates this by making the end-of-message (EOM) output low during the recording.
Recording or playback is started by closing S3. The switch must remain closed during recording and should preferably be a push-button type.
The circuit is kept simple although it is possible to connect several ICs in a cascade if longer message, or a number of short ones are to be recorded.
The bandwidth of the circuits is similar to that of telephones: ISD1012 – 4.5 kHz; , ISD1016 – 3.4 kHz and ISD1020 – 2.7 kHz. The current drain during playback is about 25mA.