ISD1820 is a single-chip voice message recording IC for single message recording and playback. It allows to record 10 sec of audio and play it back under microcontroller or by manual mode. As it consists of an inbuilt microcontroller, a message up to 10 sec long can be recorded. By connecting a resistor, these 10 secs can be extended to 20 sec. It is a non-volatile module, hence can be recorded up to 100000 times and can be stored without power. An 8-ohm speaker can be driven using the small inbuilt audio amplifier in the module.
ISD1820 chip is a resistor-controlled oscillator input (ROSC) in which sampling rate and maximum duration of audio can be controlled by placing a resistor between ROSC pin and GND, this sets oscillator frequency. The audio play volume of this module can be increased by adding AGC input to the LED output pin.