Dogs are great at detering burglars from entering one's home. This system brings the same advantage, without the need for an actual dog.
The system comes in two parts: a motion detection module (MDM) and a sound playback module (SPM). When the MDM detects motion, it sends a wireless signal to the SPM, which starts playing the sound of a large dog barking through a 3.5mm audio jack. If no further signal is received, the barking sound stops after 30 seconds.
The motion detection module is failry straightforward. It consists of an Arduino pro mini connected to an NRF24L01 transciever and HC-SR501 PIR motion sensor. A byte is sent to the SPM upon motion detection.
The sound playback module, on the other hand, is built around a cheap MP3 player that plays MP3 files stored on a micro SD card. When powered, the player automatically plays all the files of the SD card il a loop. For the purpose of this project, only the sound of a large barking dog has been written to the card, but any sound could be used. The MP3 player is controlled by an An arduino pro mini using two optocouplers which connect to where the volume buttons originally were. The Arduino is also connected to an NRF24L01 transciever to receive signals from the MDM.
The source code available on GitHub: