Project with 3914. ???

[HTAluvBeBeo]

I want to build an audio level meter. I found some schematic. But it did not work with my LM3914. Maybe it is easier with 3915 or 3916 but I can not find them in my local. So could you give me a good and simple schematic, please. I am so noob in electrics, (my major is Biz). Thank you so so much

 

[Gayan Soyza]

Did you try to rescue your problem.Here is a circuit from the data sheet.Search for the missing points in your circuit.I have built this its working fine.

**broken link removed**

 

[HTAluvBeBeo]

Thank you, I will build it again. I am using the simplest schematic from:
**broken link removed**
I always read the schematic before I begin connect wire maybe because of my bad English and noob in electronics, I don't understand all the content of the datasheet But I think the reason is LM 3914 was designed for measuring volt, not for audio power. Is it rite?? Could you give me another schematic.

When I connected 12V+ from PSU of my PC, my computer restarted

I am considering about this schem:
**broken link removed**
I don't know what is the job of OPAMP LM358, but maybe complicate schem would better??

 

[Gayan Soyza]

Rebuild your circuit nicely. Use an IC Base so it won’t damage the IC due to excess heat. The circuit I gave you is works perfectly.

LM3914 IC can use in many application’s. It used to sense analog voltage levels. See the data sheet for more details.
I think you have a short circuit in your circuit which makes the computer to restarts. Don’t give the power from the computer power supply until the circuit works perfectly.

Your second circuit is the same function like earlier circuits but the signal comes through a comparator. No need to add another comparator IC (OPAMP) for your circuit LM3914 has many built in comparators. I hope your input signal is have some adequate strength. So no need that extra IC.

 

[HTAluvBeBeo]

ok, you are rite: thank you so much there is a short circuit on my project-board, maybe it is a fault of board's fault
Thank you, again

 

[audioguru]

An LM3914 is a linear voltmeter. If it is used to measure audio levels then the lower LEDs will have wide level steps and the upper LEDs will have very close together level steps.

An LM3915 measures audio levels logarithmically. Its LEDs are all stepped 3dB apart. Each step is a little louder or quieter than the next step.

Audio has many instantaneous levels that cause the LEDs to be blurred and very dim. The datasheet for the LM3915 has a Half-wave Peak Detector circuit and the circuit posted with the LM358 opamp also has a half-wave peak detector (the opamp circuit). The peak detector holds an audio peak for a moment that is long enough for you to see its level bright and clear.

 

[HTAluvBeBeo]

OK thank audioguru, I will build the new circuit using LM358

 

[audioguru]

The circuit with the LM358 had an error on its schematic. The positive supply pin for the LM358 is pin 8, not pin 5.
I made other changes:
1) It had a 5.6k resistor for its R5 which makes the LEDs have a current of only 2.4mA. I changed it to 1k so the LEDs will be much brighter at 12mA.
2) R4 didn't do anything so it was removed.
3) The supply voltage was much too high and caused the IC to heat.
4) The unused opamp was not disabled.
5) It didn't have a supply bypass capacitor.

The absolute max negative input voltage for the LM358 is only -300mV peak. So don't have an input that exceeds 200mV RMS.

 

[HTAluvBeBeo]

Ohh, thank you so so much audioguru
I have a noob question If I use my PSU of my PC for VU Meter, what i have to do to have an input below 200mV RMS, and 6V.

 

[audioguru]

Ohh, thank you so so much audioguru
I have a noob question If I use my PSU of my PC for VU Meter, what i have to do to have an input below 200mV RMS, and 6V.

Use the line level or headphones output from your pc and keep the circuit's 100k trimpot volume control turned down so that the 10th LED lights when the signal is loud.

Use the 5V from the pc as a supply for this circuit but then white or blue LEDs won't work, use red or green LEDs.

 

[HTAluvBeBeo]

OK, thank you for spending your time to answer
more questions
In 358 datasheet, I read that pin 5 is Non-inverting input 2 and pin 8 is + VCC. So are sure that your schematic is right

Could I replace LM358 with another OPAMP which will be better and to use 12V from my PC and white or blue leds. And the Schematic would be....?
Thank you so much
I did the first vesion without 358. Now I am going to buy more part to complete the project.
Sory for my bad English , bad knowledge and asking many question.

 

[audioguru]

In 358 datasheet, I read that pin 5 is Non-inverting input 2 and pin 8 is + VCC. So are sure that your schematic is right?

Yes, pin 5 is the non-inverting input of the unused opamp. I connected it to ground to disable the opamp. Yes, pin 8 is the positive supply, the original schematic was wrong, I corrected it.

Could I replace LM358 with another OPAMP which will be better?

The LM358 is very old and is lousy. It is noisy, it has crossover distortion and its full output frequency response drops above only 6kHz.
I use MC33171 single, MC33172 dual and MC33174 quad opamps that are similar that their inputs work at the negative supply voltage and their output can go down to the negative supply voltage. Their noise is lower, they have low distortion and their full output bandwidth is to 35kHz.

to use 12V from my PC and white or blue leds.

Then the LM3915 would have much more voltage across it and therefore it will get too hot.
If you use two or three white or blue LEDs in series for each output of the LM3915 then it will work fine.

 

[TheVictim]

Are there any special considerations that need to be taken in account when using MC33171, MC33172 and MC33174's? I'm slowly getting back into electronics after a hiatus of many years and am quite comfortable with usage of the 741, 358, and 324 opamps.

Can you bias the non-inverting inputs with Vcc/2 and work from a single supply voltage?

 

[audioguru]

Can you bias the non-inverting inputs with Vcc/2 and work from a single supply voltage?

You can bias the non-inverting input of any opamp at Vcc/2 and it works fine.
The LM338 dual, LM324 quad, all the MC3317x opamps and all the MC3407x opamps work fine with their input voltages at the negative supply. Also their outputs go all the way down to the negative supply. Most opamps like the 741 don't work if the input voltages get to within 2V from the negative supply. The output of a 741 goes down to about 2V above the negative supply.

This preamp circuit has the input and output of the opamp at 0V without a signal so the LM3915 shows zero signal. 0V is the negative supply for the opamp in this circuit so a 741 opamp won't work.

Many opamps with FET inputs go crazy when an input voltage gets too close to the negative supply voltage. A TL08x and TL07x suddenly inverts when its input approaches within about 2V from the negative supply voltage.

 

[HTAluvBeBeo]

Audioguru, I saw you in many forums, you are so friendly, thank you
I think I should choose MC33171 for mono audio level meter with LM3914 ( I can not find LM3915 in my local) and MC33172 for stereo audio level meter (if the shop has MC3317x )

 

[Nigel Goodwin]

Audioguru, I saw you in many forums, you are so friendly, thank you
I think I should choose MC33171 for mono audio level meter with LM3914 ( I can not find LM3915 in my local) and MC33172 for stereo audio level meter (if the shop has MC3317x )

As already mentioned, the 3914 is a linear device, and unsuitable for audio use - it will make a VERY poor audio level meter, you really need a 3915 instead.

 

[HTAluvBeBeo]

Thank you I built one curcuit with 3914 and saw many disadvantages.
I know that 3915 is the best for my project, but I can not find any in my city Poor me, I also find it difficult to ship only two 3915 to my home...
Do you have any trick to improve the result with my 3914?

And Could you tell me the meaning of your avatar it makes me curious

 

[Nigel Goodwin]

Thank you I built one curcuit with 3914 and saw many disadvantages.
I know that 3915 is the best for my project, but I can not find any in my city Poor me, I also find it difficult to ship only two 3915 to my home...
Do you have any trick to improve the result with my 3914?

You could feed it from a log/linear convertor?, but this isn't really simple, and would make your project far more complicated. If you're going to use a 3914 make sure you use a socket for it, then you can pop a 3915 in it's place when you see how useless it is!.

And Could you tell me the meaning of your avatar it makes me curious

It's Jitsu (from Ju Jitsu, as I'm a 3rd Dan black belt and instructor), it means Art , Way, or Technique.

 

[HTAluvBeBeo]

I thoght about that convertor and search some schematic, but it seem very difficult for me
I have just gone around and loked for 3915 as weel as MC33172 but all I had was "NO, We dont have them".. Oh my poor country.
So I have to use 3914 and 358
So Sad

 

[Nigel Goodwin]

Perhaps if you had your location filled in we might know where you are?.