Hi all , i have a circuit with two LM3914 ICs and 20 LED the input of the 3914 is 2v (not starting from zero) to 7 volts for example
how can i calculate the resistor values to put in (Ref. Low) and (Ref. High) terminals of the IC to achive the desired range of volts ?
I have the data sheet but somehow i could not get that information from it ;)
sorry for ascing many questions . i am beginner !!
Thanks a lot friends :)
On page 3 of the data sheet:
What is your desired range of signal indication?
You need to create a voltage for each end of the divider to define the indicating range, and it has to be between zero and 1.5 volts less than the positive supply rail.
On page 8, they discuss how you use two resistors to program the reference regulator to produce an arbitrary voltage, and how the values of those resistors also set the LED current. This is a good way to create the desired voltage for the upper end of the divider string. You can use a resistor between the bottom end and ground to elevate the voltage of the lowest signal indicated, but you cannot calculate this resistor very accurately, because of the large tolerance of the divider resistance. You may need to try different values, or use a trim pot to set the voltage while measuring the voltage at pin 4 with a meter.
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