LM3914 calculator and build questions from an electronics newb

[goaticus]

Nevermind, turns out I am just such a noob that I misunderstood how the breadboard is laid out. The circuit works great.

**broken link removed**

 

[ericgibbs]

hi goaticus,
Thanks for letting me know that you have finally got it working.

Did you have to make any changes to the circuit design.??

 

[goaticus]

The only change I made was to the Hero's auxilary LED flasher. I changed R4 to 220K to slow the flash rate down.

 

[Elabguy]

hi everyone, I have a question about setting the reference OUT of the LM3914. I am using a 5V power for my project and I would like to set the Ref Vout to detect 3.0V at peak level. I used the equation Ref Out V = 1.25(1+ R2/R1), R2=5.1K, R1=3.6K. I expect to see a 3.02V in pin 6&7, however when I measure it, I got 3.32V. Does anyone can help me with this issue??
On page 8 of the LM3914 Datasheet, I saw another equation Vout = Vref*(1+R2/R1) + Iadj*R2. How can I calculate Iadj??? which formula should I use?? the first one or the second one???

 

[ericgibbs]

hi everyone, I have a question about setting the reference OUT of the LM3914. I am using a 5V power for my project and I would like to set the Ref Vout to detect 3.0V at peak level. I used the equation Ref Out V = 1.25(1+ R2/R1), R2=5.1K, R1=3.6K. I expect to see a 3.02V in pin 6&7, however when I measure it, I got 3.32V. Does anyone can help me with this issue??
On page 8 of the LM3914 Datasheet, I saw another equation Vout = Vref*(1+R2/R1) + Iadj*R2. How can I calculate Iadj??? which formula should I use?? the first one or the second one???

hi,
Download and install this calculator.

Woops! corrected link

https://www.electro-tech-online.com/blogs/ericgibbs/126-basic-lm3914-calculator-v3-1.html

 

[Elabguy]

Thanks ericgibbs, the calculated RefOut value by your calculator is exactly what I expected to see, but in real life, I got 3.32V on the RefOut (pin 7), do you have any idea why?

 

[ericgibbs]

Thanks ericgibbs, the calculated RefOut value by your calculator is exactly what I expected to see, but in real life, I got 3.32V on the RefOut (pin 7), do you have any idea why?

Post a diagram showing your circuit.

 

[Elabguy]

Here is it, Vin is around 4.8V

 

[ericgibbs]

hi,
With R1= 3.6K and R2=5.1K it should give a pin7 voltage of 3.02V

If R2 is actually a 5.6K you will get 3.2V, I would check the value of R2.

 

[Elabguy]

I checked it many times, R2 is 5.1K.

Anyway, do you know how to calculate Iadj from Pin8?

In the LM3914 datasheet page 8, Vout = Vref * (1+R2/R1) + Iadj*R2

Thanks for your help

 

[Elabguy]

I just checked the current Iadj with a meter, the reading is around 60uA,

Vout = Vref * (1+R2/R1) + Iadj*R2 = 3.02 + (60uA * 5.1K) = 3.32V which matches the measured Vout value, However, does anyone know how to calculate Iadj??

 

[ericgibbs]

I just checked the current Iadj with a meter, the reading is around 60uA,

Vout = Vref * (1+R2/R1) + Iadj*R2 = 3.02 + (60uA * 5.1K) = 3.32V which matches the measured Vout value, However, does anyone know how to calculate Iadj??

hi,
Look at the datasheet REFERENCE graph plot and the Adjust pin current.
It has a range of 75uA to 120uA

If you have 60uA then the second term, Iadj * 5100 = 60uA * 5100 =.306v

and the first term Vref[1+R1/R2] = 1.25 * 2.41 = 3.02V so that gives a Vout of 3.32V which is what you are measuring.

Its important to note that there is wide spread in the parameters of the LM3914.
I would recommend that R2 is a variable resistor, in your project a 10K could be set to give the required Vout/ref

 

[gilfrid]

Lm3914a.exe

I noticed that Eric posted images of the output from his LM3914a.exe.

I have tried to find this exe on the net but with no luck.

Any chance of anyone (Eric?) posting this exe?

It would be most kind.

Regards
Andrew

 

[SODA]

hi goaticus,
Give me a minute just got my wires crossed at this end...
I will repost.
EDIT:
Here we go.
Look at this image, set up the LM3914 this way.

To Calibrate the sensor amp I would use a 100R variable resistor to simulate the tank sensor.
At first set both the Zero and Span pots to 50% rotation.

1. Set the sensor sim resistor to 77R and adjust the Zero so that LED#1 lights.
2. Set the sensor sim resistor to 7R and adjust the Span so that LED#10 lights
repeat this from line number 1 until the LED's are LED#1 for 77R and LED#10 for 7R

OK.

The pic you just show. Is it part of another program or is it a software program on itself. If it is, please give me the link