The circuit Bargraph Voltage Indicator used IC op-amp two quad voltage comparators to illuminate a series of 4 LEDs indicating volume level.
The op-amp used in this particular circuit is the LM339. It is a popular IC and should be available from many parts stores…..
Read more : Bargraph Voltage Indicator by LM339
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Audible Logic Probe
Windows Comparator [...]
Useful for power lines control
Simple, transformerless circuitry
This circuit, designed on request, has proven to be useful to indicate when the voltage in a power supply line is changing from 120V to 240Vac. It can be used in different circumstances and circuits, mainly when an increase in ac or dc supply voltage needs to be detected.
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This is a mains 230V AC voltage indicator and is a LIVE CIRCUIT, so take care.
The Resistor has to be a fusible ceramic wire wound and the capacitor 630V AC or higher capacity.
Read more : Mains Voltage Indicator with a LED
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