ISD1820-based recorder

ISD1820 Chip Introduction:
Operating voltage 3-5V;
built-in 8Ω speaker driver amplifier circuit, capable of directly driving an 8Ω 0.5W speaker;
Pin 1 is the recording input (REC), active high. Recording begins as soon as REC goes high (regardless of whether the chip is in power-saving mode or playing audio). REC must remain high during recording. Recording ends when REC goes low or memory is full, and the chip automatically writes an end-of-memory (EOM) flag to promptly stop subsequent playback operations.
Pin 2 is the edge-triggered playback input (PLAYE). Playback begins when a rising edge appears at this pin. Playback continues until the EOM flag is displayed or memory ends. PLAYE can be released after playback begins.
Pin 3 is the level-triggered playback input (PLAYL). Playback begins when this pin changes from low to high. Playback continues until this pin returns to low, the EOM flag is encountered, or memory ends.
Pin 4 is the microphone input (MIC).
Pin 5 is the microphone reference (MICREF).
Pin 6 is the automatic gain control (AGC) terminal. A 4.7μF capacitor typically provides satisfactory results in most cases.
Pins 7 and 9 are the speaker output terminals (SP+, SP-), which can directly drive speakers of 8Ω or higher.
Pins 8 and 14 are the ground terminals (VSSA, VSSD), where the different ground lines of the chip's internal analog and digital circuits converge.
Pin 10 is the oscillation resistor terminal (ROSC), connected to the oscillation resistor in the VSS circuit; the resistance value determines the recording and playback time.
Pin 11 is the power supply terminal (VCC), where the different power buses used by the chip's internal analog and digital circuits converge, minimizing noise. Decoupling capacitors should be placed as close to the chip as possible.
Pin 12 is the pass-through mode terminal (FT), allowing external voice signals connected to the MIC input to pass through the chip's internal AGC circuit, filter, and speaker driver directly to the speaker output, forming a microphone amplifier function. Normally, the FT pin is low. To achieve pass-through functionality, the FT pin must be connected to a high level, while REC, PLAYE, and PLAYL remain low.
Pin 13 is the recording indicator (/RECLED). When recording is in progress, this pin is low and can drive the LED. Additionally, when playback encounters the EOM mark, this pin outputs a low-level pulse. This pulse can be used to trigger PLAYE for loop playback.




This project is for initial training purposes and will undergo continuous optimization and adjustments.