Low-voltage monitoring circuit for a nominal 24V DC input. The TL431 threshold detector and BC547B driver activate a 5V active buzzer when PLUS drops below about 19.5V.

Active (driven circuit included) 85dB@5V,10cm Magnetic 2700Hz Plugin,D=12mm Buzzers ROHS #CommonPartsLibrary #Audio #Vibration-Motor #Buzzer

4-layer marine GPS timing and communication device using nRF52840, u-blox ZED-F9P GNSS with external active antenna via u.FL, 915 MHz LoRa radio, Li-ion battery with USB-C charging, separate clean GNSS LDO and digital 3.3V rail, SPI memory LCD, RGB LEDs, buzzer, and 6-axis IMU. PCB target is a 70 mm circular layout with strict RF zoning, dedicated ground plane, 50 ohm RF traces, physical separation between GNSS and LoRa, and low-noise placement suitable for harsh marine environments.