This is a Simple Reverse Polarity alarm by Sound(buzzer) and Light(LED display). To use such circuits. If you have identified the polarity of the power supply or power supply connector on the wafer is not clear.
The wrong polarity can cause damage and range. But when using this circuit with an active circuit, it can protect and show a correct polarity.
Operation of the circuit is not complicated. When the supply terminals to make LED1 and D1 bias direct. It makes LED1 light, and The piezo speaker PZ1 emit noise.
The lamp LED1, it would be R1, assist current limiting and voltage. To prevent LED1, no damage. But if the supply polarity is LED1, D1 will actuate bias. D1 does not bias the LED1 not lit.
And piezo speaker PZ1 not emit noise. The D2 works, The D2 works, because of it is direct bias. Make a power supply circuit as usual
Build reverse polarity alarm
This circuit is easy you can use a universal PCB board to builds as Figure 2 is components layout.
Figure 2 The components layout
The components List
Resistors ¼W +5%
Keep reading: A diode protect CMOS circuit
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