Null detector ( polarity tester ) circuit diagram

It’s very easy to test the polarity of a signal at a point from circuit ( if the voltage from test point is positive or negative ) by using a digital multimeter or using a electronic an electronic circuit like in this diagram .  This polarity tester ( null detector ) circuit diagram is based on a common 741 operational amplifier that require few additional components to do the null detection .  The test result of the polarity indicator is displayed through the two LED’s  LED1 and LED2 .

This null detector circuit diagram need to be powered by a 12-15 volts DC power source .

For a easy identification of the null you can use two different color LED’s .