This is simple electronic project which we implemented for some local event to guide audience automatically with some prerecorded voice messages. The core component of this unit is ISD1820PY voice record/playback chip which is manufactured by Nuvoton Technologies. Except to ISD1820PY, this unit use commonly available low power LASER and LDR assembly to detect people. To drive the loudspeaker we use popular LM386 audio power amplifier.

Basic setup of electronic voice messenger.

Thanks to ISD1820PY and LM386 this system can implemented on breadboard or on strip-board with minimum number of external components. This circuit is designed to drive using 6V or 9V DC battery but it can also drive with 6V or 9V DC regulated power supply. To get 3.3V we use LD1117V33 voltage regulator, but this can also be replaced with some commonly available 3.3V regulators such as LD33V, MC33269-3.3, etc. For the speaker we use 4-inch 8Ω full-range speaker.

This unit can used with both dynamic and condenser microphones but according to our experiments, ISD1820PY produces excellent results with dynamic microphones. As per our observation with some condenser microphones results are not up to the satisfactory level.

To program voice message hold down S1 push switch, and record the message. Once message is finished, release S1 push switch to get system into the playback mode. According to the manufacturer ISD1820PY use on-chip flash memory to store voice messages and it can program up to (minimum of) 100,000 cycles.

Project Related Downloads

Detailed schematic of light operated voice messenger.


ISD1820PY - Single-chip, single-message voice record/playback device, 6 to 16 second duration.
LM386N-4 - Low Voltage Audio Power Amplifier.
LD1117V33 - 3.3V 800mA LDO Voltage Regulator.
KSP92 - 300V 0.5A PNP Epitaxial Silicon Transistor.