Application of the voice processor APR9600.
Application of the low-power audio amplifier LM386.
The Voice Recording and Playback System enables recording a single message of up to 60 seconds duration (or eight different messages of 7.5 seconds duration each). In the playback mode, the circuit plays recorded message either randomly or in a sequential fashion.
No. of ICs used: 2
Voice signal from the microphone is fed into the chip through a differential amplifier. It is further amplified by connecting Ana_Out (pin 21) to Ana_In(pin 20) via an external DC blocking capacitor C1. A bias signal is applied to the microphone and to save power during playback, the ground return of this bias network can be connected to the normally open side of the record switch. Both Mic. in and Mic.Ref (pins 18 and 19) must be coupled to the microphone network through capacitors.
An internal anti-aliasing filter automatically adjusts its response according to the sampling frequency selected. Then the signal is processed into the memory array through a combination of the sample- and-hold circuit and analogue read/write circuit.
The incoming voice signalsare sampled and the instantaneous voltage samples are stored in the non-volatile flash memory cells in 8-bit binary encoded format.
During playback, the stored signals are ret r ieved f rom the memory, smoothed to form a continuous signal, low-pass filtered and then amplified.The signal level at
the speaker terminals SP+ and SP- (pins 14 and 15, respectively) is at about 12mW power into 16-ohm impedance. The output from pin 14 (SP+) is further amplified by the low-power amplifier using LM386 (IC2) as shown in the figure. The recorded
message is reproduced into speaker LS1.
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