Homemade simple automatic message machine

1. Component selection

C1 selects a small leakage current; the relay selects a small reed relay with working voltage ≤6V, pickup current ≤15mA, contact withstand voltage >220V, contact current >0.1A; resistance R1 <500kΩ.

2. Working principle

When in use, press the recording button of the recorder, close K1, and place the words "The owner is not at home, please ring the doorbell, and I will record for you for two minutes" on the door. If you find that the LED light is on when you come back, it means that the guest has been here. Rewind and play back the recording to know the guest's message. But don't forget to switch K1 off and on once, otherwise the LED light will always be on.