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Lm3914 5 to 14 volts

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bryan91

New Member
i need to design a circuit to measure the voltage from a psu in steps of one volt. i need it to range from 4 volts to 15 volts in steps of one volt. i was told to use the lm3914 and a 10 Led display. i cant seem to get this to work. i have it working between 12 to 15 volts but dont know how to adjust the steps to one volt steps. what resistor values do i need and how do i wire this all up?? oh and by the way i have the use the input voltage to power this too...
Thanks in advance!
 

bryan91

New Member
here ya go i got it off another website
 

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MikeMl

Well-Known Member
Most Helpful Member

bryan91

New Member
yup thanks! but doesn give me the values i need to achieve this?? i cant seem to understand it? in the schematic above im lookin to change these values to modify it to work between 5 to 14 volts. help is greatly appreciated!
 

MikeMl

Well-Known Member
Most Helpful Member
Where is Eric or Audioguru, when you need them???
 

bryan91

New Member
well its a project i have to do for college so the sooner the better please?? its going to be mounted onto the psu housing to monitor its output and show me the different voltages its producing...
 

audioguru

Well-Known Member
Most Helpful Member
I didn't look at Eric's calculator because setting the LM3914 is so simple:
On the circuit that was posted:
1) R3 sets the amount of LED current. Since pin 8 is grounded then R3 has 1.25V across it and Ohm's Law calculates its current. The datasheet shows a graph of the LED current that depends on how much current is in R3.

2) Pin 6 is at the top of the resistor ladder in the IC and sets the voltage that lights the 10th LED.

3) Pin 4 is at the bottom of the resistor ladder and sets the voltage that lights the first LED.

4) The problem is that the total value of the resistor ladder varies a lot from IC to IC so trimpots must be used to set accurate voltages.
 

bryan91

New Member
hey thanks for all the help! i finally managed to get it working with ur help and a little fiddling around with resistor values! thanks :)
 

alex69

New Member
:) fine.
I'm also happy when my circuits works fine but... you must understand why and how thy works.
alex
 

bryan91

New Member
i figured out i had the lower limit resistor limit set wrong so wasn doing it right for me! but signed off and all now only need to build it on stripboard now and den im done!
 
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