Voice recorder/playback circuit

Description.
This circuit is designed in response to a request made by Mr Vignesh. What he requested was a circuit for recording and playing voice. I think this circuit is enough for the purpose. This circuit is based on the IC ISD1020A from ISD. The ISD1020A is a CMOS single chip record/playback device. The chip can record voice for 20seconds and has many features like automatic gain control, anti aliasing filter, built in audio amplifier and smoothing filter. The IC is fully compatible to microprocessors and can be used for a myriad of applications. The voice is stored in their natural form in the non-volatile memory cells inside the IC which enables a high quality reproduction. The recorder voice can be retained in the chip for as long as 100 years and the chip is capable to have a 100000 read/write cycles.

The circuit is designed as per the application diagram in the datasheet.Pin23(CE) is the chip enable pin and it has to be held low using switch S1 in order to perform a record or playback cycle. Pin 27 (P/R) is the playback/record pin and a high level on it selects a playback cycle while a low level on it selects a record cycle. The selection can be done using the switch S3.The pin 24 (PD) is the power down pin. It has to be held high using switch S2 in order to pull the device to a extremely low power mode while there is no recording or playback (idle state).The resistor R1 and capacitor C1 determines the release time of the internal AGC circuit. The resistor R5 and capacitor C5 connected across the pin 20 and pin 21 provides an additional cut-off to the low frequency end of the voice pass band.

Circuit diagram.

Notes.

• The circuit must be assembled on a good quality PCB.
• The circuit can be powered from a 5V DC source.
• Switches S1 to S3 must be miniature SPDT switches.
• Speaker K2 can be a 16 Ω loud speaker.
• K1 can be an electret microphone.