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ryeeson

Input signal for LM3915. need help.

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1.What does the singnal Rhi do?

It is the top of the resistor ladder that applies reference voltages to the comparators in the LM3915. Its voltage sets the voltage thresholds at the input that turn on the LEDs.
If Rhi is at 5V (and Rlow is at ground) then a 5V input is needed to light the 10th LED.

The voltage of Rhi changes with the input volume in my project for automatic volume control. Your circuit should have it connected to a regulated 5.0V. Then the transistor, resistors and capacitor connected to it in my circuit aren't needed.

2.Why use voltage regulatro since the supplied power is DC?

Batteries have an internal resistance that gets higher as the battery runs down. The internal resistance causes the battery voltage to jump up and down as the load current changes. LEDs have a fairly high current and the LM3915 adds and subtracts them during its display and the fluctuating battery voltage was amplified by the mic preamp.

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3. The R16 is a power resistor?

Since mine is not powered by batteries, i dont need the Voltage regulator. am i right?
you have mantion that this circuit has additional range about 20db. i dont get it! what range are they?

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Automatic gain control huh.. amazing

theoryticly, changing the capasitor from 10v to a bigger(let say 50v) would slow down the charging process. What acctuly happend if i use 50v capasitor instead of 10v? 

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Automatic gain control huh.. amazing

Yeah, it fixes a problem I had with an old sound meter project with two LM3915's like yours, but it showed either a very low level or a very high level. This one always indicates between 0 and 10.

theoryticly, changing the capasitor from 10v to a bigger(let say 50v) would slow down the charging process. What acctuly happend if i use 50v capasitor instead of 10v?

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Can i use this circuit in my project? but i dont need the very low sound. There is two thing i can do.

1st, i can add a high pass filter to the signal before the lm3915 input.

2nd, i can modify the circuit. in my opinion by changing the value of the R10(from 100k to 10k) will cut the low signal since the current have less resistance to the ground compare to the R8. am i correct?

or by changing the R15 as you have mantion?

With this 2 option, which one would u prefer/suggest?

i cannot see how the Q3 act as a peak detector. again, i dont need the peak detector. i need average detector. How should i modify it? 

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Can i use this circuit in my project? but i dont need the very low sound. There is two thing i can do.

1st, i can add a high pass filter to the signal before the lm3915 input.

2nd, i can modify the circuit. in my opinion by changing the value of the R10(from 100k to 10k) will cut the low signal since the current have less resistance to the ground compare to the R8. am i correct?

or by changing the R15 as you have mantion?

With this 2 option, which one would u prefer/suggest?

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my project objecitive is to detect a noise in the library. this subject to noise caused when people(library user) talk louder. All those noise from low frequency is not a problem since it wont 'disturb' user.

i want to filter a frequency from 0 to 1000 Hz.   

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my project objecitive is to detect a noise in the library. this subject to noise caused when people(library user) talk louder. All those noise from low frequency is not a problem since it wont 'disturb' user.

i want to filter a frequency from 0 to 1000 Hz.

post-1706-14279142615708_thumb.png

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Hello Audioguru,

i've tried your project but i use the MC33171.
sorry but i can't figure out where is your modified average detector. 
i've been work hard to understand your design. There is some question i would like to confirm with u.

1. When we do circuit analysis considering in DC signal, we don't include the capacitor(so inductor) in our analysis. The inductor become open circuit and the capacitor become short circuit. Am i correct? in the 1stage, you used an non-inverting op-amp. why we need the voltage divider? and what is the point of R3 connecting to the ground?

You said that,

"With low-level sounds, R15 in series with the resistor ladder at pin 6 creates 0.5V at pin 6. Therefore an input signal of only 0.5V lights the 10th LED. 15.8mV lights the 1st LED."

my question is,
1.what happen if with high-level sound?
so if with a low-level signal, there is no current from Q3 to R14? which will connect the 5v through R15 to pin 6(LM3915)? but that should provide pin 6 with 5v instead of 0.5 as you have mention.
i need to alter the Rhi so that the 10th LED will light up if the input signal is high enough(i mean if the sound level is loud considering inside the library).


i've check the output signal with an oscilloscope. The signal is something unusual for me. If i take reading form output on pin 7 of the opAmp(take your circuit as a reference), the signal seem have been half wave rectified. I've built a circuit exactly with your and take the band pass filter that you have suggest.
The circuit works well but it's sensitivity is too much for me. When i talk softly, the 10th LED already light Up. (i operate it on dot mode). the sound-level around me never lights the first 3 LEDs. its always lights the 5th to 10th LED.

How can i alter this? Can i alter this by changing the R15?
may be i get it wrong.. the sensitivity is okay. But what i want to to is to control the LED. Let say i want the 10th led only lights if i the sound level is high enough example someone talk too loud or  if i talk softly, the 3rd and 4th LED light up.
or probably i just cascade the LM3915 but seem it wont work.

I really appreciates your help.

 

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Hello again. I've reduce the circuit gain by reducing the value of R5. And
i'm happy with it. There is something i want to come up with after changing the
R5 to a lower value (eg. 40k) there is no LED light up on the beginning (no sound).
When I talk, the LED will lights accordingly but the problem is even if I talk
Softly, the 10th LED will light. When I stop talking, all the LED is off.
Another problem is the LED lights very fast. How can we make it have a little delay?
So that we can catch our eyes on the LED display level?

When I change the R5 to a very low value, the circuit cannot pick up any signal.
How to make the LED less sensitive without sacrifice its 'true gain' so that the next LED
Is harder to lights. Example, for normal library environment we set (guess) the
1st to 3rd LED is lights up (due to the air conditional unit noise) and this
Level stay until someone makes a sound (talking etc)
Which causes the 4th (to 5th...etc according to the sound level) to light up.

Now the display level is seem not more then 30dB. That why I’m thought of cascading
The LM3915.
Or... it may be because your circuit is using the average detector shown bellow.
May be I just need to change the peak detector to the average detector? (As shown in
Picture 2?) But your peak detector seem don’t match with the one in the data sheet.

peak detector



average

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I've reduce the circuit gain by reducing the value of R5. And i'm happy with it.

Good.

There is something i want to come up with after changing the R5 to a lower value (eg. 40k) there is no LED light up on the beginning (no sound).

Normal.

When I talk, the LED will lights accordingly but the problem is even if I talk
Softly, the 10th LED will light. When I stop talking, all the LED is off.
Another problem is the LED lights very fast. How can we make it have a little delay?
So that we can catch our eyes on the LED display level?

My peak detector responds very quickly, holds the level for a moment then slowly drops away. It drops away quick enough to show the loudness of each spoken word and bounces with music.
The 10th LED should light only if the level is higher than the amount to cause all other LEDs to light. If the 10th LED is lighting out of sequence then the supply needs bypassing with a capacitor as shown in the datasheet.
An average detector will respond slower and have equal rise and fall times. 

When I change the R5 to a very low value, the circuit cannot pick up any signal.

Normal.

How to make the LED less sensitive without sacrifice its 'true gain' so that the next LED
Is harder to lights. Example, for normal library environment we set (guess) the
1st to 3rd LED is lights up (due to the air conditional unit noise) and this
Level stay until someone makes a sound (talking etc)
Which causes the 4th (to 5th...etc according to the sound level) to light up.

The steps between the LEDs lighting in an LM3915 are 3dB apart. 3dB is a small change in sound level.

Now the display level is seem not more then 30dB. That why I’m thought of cascading
The LM3915.

30dB is a wide range of sound level. Cascading two LM3915 ICs will make a range of 60dB which is much too wide.

Or... it may be because your circuit is using the average detector shown bellow.
May be I just need to change the peak detector to the average detector? (As shown in
Picture 2?) But your peak detector seem don’t match with the one in the data sheet.

My circuit uses a peak detector with a fast rise time and a slow fall time.
An average detector might be better for your application but the circuit in the datasheet needs positive and negative supplies for it.

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hello again,



i cannot see the dual supply for the data sheet. Where am i suppose to connect the negative supply?

How to change the led lights so that it lights not too fast and light off not to fast also?

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i cannot see the dual supply for the data sheet. Where am i suppose to connect the negative supply?

They assume that you know so they don't show power supplies for the opamps.
Each opamp is an inverter with the non-inverting input connected to ground. Therefore the outputs must swing equally negative as well as positive. Ordinary opamps are shown that don't work if their input voltage is anywhere near a supply voltage.

How to change the led lights so that it lights not too fast and light off not to fast also?

Increase the value of C2 in the average detector to slow down its rise and fall times.

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my bad.. i dint check the LM and LF datasheet  :'(

ok thanks for the advice. btw  can i just replace your peak detector shown in the figure bellow(link)

with the average detector? or do have some suggestion?

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you mean. i dont need transistor Q1,Q2 and Q3?
so the output signal from pin7 should connect to
my average detector? the rectified signal should connect to signal input on pin 5 of LM3915 right?

then i'll update you soon. thankx

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you mean. i dont need transistor Q1,Q2 and Q3?
so the output signal from pin7 should connect to
my average detector? the rectified signal should connect to signal input on pin 5 of LM3915 right?

Correct. I used the transistors to provide very high charging currents to the capacitors in the peak detectors so they charge very quickly.

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