Then connect a high value potentiometer at the 4th pin, adjust it until LED1 glows alone. Now connect a low voltage at the input after removing high voltage. For this just eliminate the resistor R3 and connect the high voltage (less than 25V) to the input and adjust the potentiometer until the 10th LED glows (in dot mode). When switch is closed, pin 9 of the IC gets connected to the positive supply, then bar graph mode is enabled. To select dot mode or bar graph mode a switch is given at the 9th pin. The outputs pins of LM3914 are compatible for both TTL and CMOS. We can control the brightness of LED by programming via an external resistor. The IC LM3914 can operate with a wide range of supply voltage (3V to 25V DC). It is basically a milli volt measuring IC which is able to convert a varying milli volt input into a corresponding LED indication like a linear analog display. You can alter this DIY battery level indicator circuit for monitoring and displaying other voltages also. Our circuit is most suitable for 12 volt battery status indication because we are calibrating it for 12V battery. This can also be used as a low battery voltage indicator circuit as it displays low voltage if you calibrate it to do so. We have already posted a temperature level sensor using this same IC (LM3914). Rive a display of 10 LEDs in dot mode or bar mode. No external power supply will be needed for the circuit, and it will run on the same battery. With the 100 K variable resistor, the beeping signals and the LED flash rate can be changed. As the battery runs down and reaches the preset level it will send beep signals and flash an LED. Telephone Circuits ▼ Telephone Circuits Two transistors and a 555 timer IC are used at the circuit.Converter Circuits ▼ Converter Circuits.Oscillator Circuits ▼ Oscillator Circuits.
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