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lm3914 & lm3915

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chuck

New Member
I make with some simple circuits. I have a lot of questions on this hobby. I want to build a 10 led voltage indicating circuit for 5 to 15 volts, d.c. Bought several lm3915. Will the lm3915 work or do I need the lm3914? I would like the results to be 1.0 volt per led. Thank you for any help.
 

kpatz

New Member
The 3914 has linear steps so you can calibrate it to 1v/LED. The 3915 has logarithmic steps so you won't be able to get a 1V/LED scale with that chip.
 

audioguru

Well-Known Member
Most Helpful Member
The logarithmic steps in an LM3915 is made for measuring sound and light levels.
 

jianwei

New Member
Using a 10 led bargraph,

how to I build a 0 ~ 5V led bargraph.
Since there are 10 led i presume, how i make increase 0.5V will light up 1 bar , 2 bar when 1V etc..

Any circuit diagram I can refer to?
 

Roff

Well-Known Member
Using a 10 led bargraph,

how to I build a 0 ~ 5V led bargraph.
Since there are 10 led i presume, how i make increase 0.5V will light up 1 bar , 2 bar when 1V etc..

Any circuit diagram I can refer to?
Have you looked at the datasheet? Use the schematic on page 2.
 

crutschow

Well-Known Member
Most Helpful Member
I make with some simple circuits. I have a lot of questions on this hobby. I want to build a 10 led voltage indicating circuit for 5 to 15 volts, d.c. Bought several lm3915. Will the lm3915 work or do I need the lm3914? I would like the results to be 1.0 volt per led. Thank you for any help.
Along with using an LM3914 your will need a reference voltage and op amp to offset the input 5V to display the 10V to 15V input range you want.
 

audioguru

Well-Known Member
Most Helpful Member
Along with using an LM3914 your will need a reference voltage and op amp to offset the input 5V to display the 10V to 15V input range you want.
The LM3914 has a built-in adjustable voltage reference. It has enough current to set the range from 10V to 15V without an additional opamp.
 

Roff

Well-Known Member
If chuck has a V+ between 16.5V and 20V, he could set up the internal reference to 5V and apply that to RLO, amplify the 5V reference to 15V with a gain-of-3 op amp, and apply that to RHI. Then the input signal would not require level shifting.
 

chuck

New Member
Thanks for all the help and input. I built the circuit using the lm3914. It works well. I really appreciate your help.
 

Nebel

New Member
hi all!
Can you tell me pls in detail, how can i increase low threshold of input signal?
I built VU meter with 0...1v range and now i want build meter with 1...2v range and then use they as single 20 leds meter with 0...2 v range.
Can you add short scheme if possible.
 

audioguru

Well-Known Member
Most Helpful Member
hi all!
Can you tell me pls in detail, how can i increase low threshold of input signal?
I built VU meter with 0...1v range and now i want build meter with 1...2v range and then use they as single 20 leds meter with 0...2 v range.
Can you add short scheme if possible.
The datasheets for the LM3914 and the LM3915 show how to cascade two ICs so that the total number of steps is 20. I made one about 30 years ago.
 

Nebel

New Member
yes, i read datasheet, but not quite understand how specifically regulated
threshold of 2nd IC.
Is the R6 regulated low threshold ?
 

audioguru

Well-Known Member
Most Helpful Member
The ratio of the resistors determine the reference voltage of each LM3915 IC.
The reference voltage at pin 6 determines how much input voltage lights each LED.
They are 30dB apart from each other so that the lowest one displays up to 0.3V and the highest one displays up to 10V.
 

Nebel

New Member
so, is this sheme correct?

R1 regulated high threshol of IC1, grounded pin4 set low threshold of IC1 to 0v.
R2 regulated high threshol of IC2, voltage from Rhi (pin6) of IC1 shift low threshold of IC2 to 1v.
 

Roff

Well-Known Member
That's the circuit for the LM3914 display, which is linear. LM3915 is logarithmic, so your best approach would be to use fig. 5 or fig. 6 in the datasheet. Read the accompanying text. The LM3915 needs 10V full scale audio to accurately display 60dB dynamic range. Amplify your 2V input signal by 5.
 
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Nebel

New Member
that sheme work not bad, but i think i will use single IC with shifted zero, for better visibility.
In any case cascaded lm3915 will give something like this:

or i am wrong?

anyway thanks all for help!:)
 

audioguru

Well-Known Member
Most Helpful Member
that sheme work not bad, but i think i will use single IC with shifted zero, for better visibility.
In any case cascaded lm3915 will give something like this:
The numbers on your graph do not have a label. Are they temperature or weight? The weeks in a year?

The LM3914 is linear. There is 10% of full scale between each LED turning on.

The LM3915 is logarithmic. There is 3dB between each LED turning on.
 
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