![]() ![]() When Vin is less than Vref the output on pin goes to about 10-volts turning on transistor Q1 which turns on the LED. ![]() 2 with the addition of Q1 to act as an open collector output driver. The LM358 is designed for single supply operation. 2 uses a LM358 op-amp instead of the LM741. Single supply- click picture for full size. The disadvantage of using the LM741 is the use of a bipolar power supply. If we adjust the 10K pot to where Vin is greater than Vref the output on pin 7 goes to about plus 10-volts forward biasing the 1N4001 and turning on the LED. Here we use a 1N4001 diode to protect the LED from excessive reverse voltage. If Vin is less than 6-volts the output on pin 7 of the LM741 will be about minus 10-volts. On the POS input on pin 3 we connect a potentiometer back to + and GND. In the NEG input on pin 2 is fixed at 6-volts with a Zener diode connected to the + side of the power supply. ![]() In this test circuit we use a 12-volt bipolar power supply. 2 is a comparator built from a common LM741 op amp. It's either all the way ON (near Vcc) or OFF (near 0 volts). Comparator BasicsĪ comparator is often an operational amplifier without feedback between the inputs and output. The voltage divider resistors and the 100K pot set the trip on voltages. LM339 based 4-bit voltage indicator - click picture for full size.Ībove we are using all four comparators in the LM339 as a 4-bit voltmeter. In another case I used a LM339 quad comparator to build a non-microcontroller based battery charger based on the circuit in Fig. In my Arduino Analog to Digital Conversion Voltmeter I generated a variable voltage with the Arduino pulse-width-modulation with the use of a comparator to measure an input voltage up to 20-volts - far above the 5-volt digital logic. They are used internally within Arduino making analog-to-digital conversion (ADC) possible when used with a digital-to-analog voltage converter (DAC). Often having two inputs they output a HIGH or LOW based on the relationship of those inputs. Comparators are every for allowing digital circuits and micro-controllers to interface with analog voltages in the real world. ![]()
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