There are various types of voice processing chip (IC) with various features for speech compression and processing is readily available. Here is projects called Voice recording and play back using chip (APR9600). An APR9600 is a single chip voice recorder and playback device from Aplus integrated circuits. This chip used flash non volatile memory to store up to 256 voltage levels. i.e. for 32 to 60 seconds.
This chip have many features like, one can select sample rates with consequent quality and recording times. Microphone amplifier, automatic gain control (AGC) circuit, intends anti-aliasing filter, integrated output amplifier and measure management etc.
Circuit Description of Voice Recording and Playback Using APR9600:-
The circuit of voice recording and playback is build around chip APR9600 (IC1). The recordable sound is changed to voice signal using microphone and given to IC1 through differential amplifier. This signal is further amplifier by inbuilt pre-amplifier and by connecting pin 21 to pin 20 via an external DC locking capacitor C1. In order to save power supply a bias signal applied to microphone while playing, the ground return of this bias network is connected to normally to open side of record switch. Microphone connected to IC through couple capacitors C3 and C4 respectively as shown in circuit diagram.
According to sample frequency selected for recording, inter anti-aliasing is automatic adjusted its response. Now, this signal proceed into the memory through combination of sample and hold circuit and analogue read/write circuit. The given voice signal and first sampled and then the corresponding instantaneous voltage samples are stored in the non-volatile flash memory cell in 8-bit binary encoded format.
PARTS LIST OF VOICE RECORDING AND PLAY BACK CIRCUIT USING APR9600
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1, R2, R4 – R6, R15 = 100 KΩ
R3, R8 = 390 Ω R7 = 220 KΩ R9 = 1 Ω R10 = 33 KΩ R11 = 5 KΩ R12, R13 = 4.7 KΩ R14 = 1 KΩ VR1 = 10 KΩ |
| Capacitors |
| C1, C3, C4, C6, C8, C9, C11 = 0.1 µF (Ceramic Disc)
C2 = 4.7 µF, 16V (Electrolytic Capacitor) C5, C14 = 22 µF, 16V (Electrolytic Capacitor) C7, C13 = 100 µF, 16V (Electrolytic Capacitor) C10 = 0.47 µF, 16V (Electrolytic Capacitor) C12 = 220 µF, 25V (Electrolytic Capacitor) |
| Semiconductors |
| IC1 = APR9600 (Sound Record Play IC)
IC2 = LM386 (Low Voltage Audio Power Amplifier) T1 – T3 = BC557 (PNP General Purpose Transistor) D1 = 1N4001 (Rectifier Diode) LED1, LED2, LED3 |
| Miscellaneous |
| MIC1 = Condenser microphone
LS1 = Loud speaker SW1, SW2 = Push to on switch SW3 = ON/OFF Switch |