This code works on a ATMEGA Tiny 84 MCU. It protects loudspeakers connected to a poweramp from bad condition like DC on output, to hight current. Also it protects the poweramp from short circuit. It has power on delay to prevent audible plops and drives status LEDs.
The hardware uses low Rdson MOSFET to form a solid state relay for fast switching high current audio signals. No more burned contacts in electromechanical relays.
The system was developed to work with SMPS that provides a power good signal and a standby DC output of 8-15 Volt/100mA. Alternate linear PSU is also possible, see below. When Power On/Good signal detected then LED D6 starts flashes for 5 seconds and then turns speaker and D6 on.
The firmware continously monitors amp AC current, temperature and DC level over interface logic. On any malfunction it switches speaker outputs immediately off and signals error condition by LED. The overtemperature sensor can be some kind of bimetal switch. (open contact on high temperature) Preferably mounted on amp heatsink.
To reset the error condition a powercycle is required.
Version 1.0 introduces several new functions and uses a new PCB board
Instead of different LED for each error condition, by setting JP1 a 2 LED signaling option may be selected. LED D6 does not change. LED D2 and D3 are not used anymore.
D5 signals standby and error condition by flash codes. While standby D6 lights continuosly dimmed. It goes off while no errer is detected. On any error it flashes 1sec. on, 1sec off, then one, two or three times short flashes.
- one short flash = Error: overcurrent
- two short flashes = Error: DC detect
- three short flashes = Error: Overtemperature
If not using on board LED, one can assemble 2 or 3 PIN 2.54mm headers to connect remote LEDs. With new display option even a single bicolor LED (red/green) can be used.
Linear power supply do not provide power on/good signal. One can assemble the necessary parts to the PCB in such case. See schematic for details.