Now, here is one another basic electronic project using the most versatile operational amplifier IC 741 “DC Volt Polarity Indicator”. Using the project DC volt polarity indicator one can know the positive and negative polarity of DC volt. This project is very useful for electronics hobbyist in order to check either battery polarity or polarity at output of DC source. The circuit present here is so simple that even electronics beginners can understand how circuit works.
Circuit Description of DC Volt Indicator Using IC 741
The heart of the circuit DC volt polarity indicator is op-amp 741, which is here used in Non-inverting mode. Power supply is given to the circuit through positive (+) and negative (-) line. DC Polarity to be tested is connected to Vin pin (pin 3) of IC1 via resistor R1. If positive DC volt is given to Vin pin, DC positive volt is appeared at output pin (pin 6) and if negative volt is connected to Vin pin, DC negative volt is appeared at output pin (pin 6). The output of IC1 is connected to LED1 and LED2 via resistor R4 which is used here as current limiter. Glowing LED1 (RED LED) indicate negative DC volt and glowing LED2 (GREEN LED) indicate positive DC volt.
PARTS LIST OF DC VOLT POLARITY INDICATOR USING IC 741
Resistor (all ¼-watt, ± 5% Carbon)
R1 = 100 KΩ
R2 = 680 Ω
R3 = 100 KΩ
R4 = 560 Ω
VR1 = 10 KΩ
IC1 = 741
LED1 = RED LED
LED2 = GREEN LED