Sound Level Indicator

[jon1]

Hi AudioGuru,

Thanks for the answer, I'll try with your infos... I'll come back for more questions if needed..

J.

 

[jon1]

Hi AudioGuru,

It's me again. I want to know how many LEDs will light for how much dB if the range of the Sound Level Indicator is 45 dB to 95 dB? And another thing, who can it be 45 dB to 95 dB, the LM3195 only has 10 outputs in 3 dB steps for a total of 30 dB?

J.

 

[audioguru2]

Hi Jon,
Yes the LM3915 has a range of only 30dB. But I designed the circuit to have an additional 20dB of automatic gain control.

For low level sounds, the input is indicated directly on the LEDs of the LM3915.
For low level sounds, the Rhi voltage of the LM3915 is set by the voltage divider of R15 (220k) and the LM3915 divider's resistance of 28k. So the voltage is only 0.56VDC.

For loud sounds, Transistor Q3 increases the voltage of Rhi to about 5.6V which is 20dB higher.

 

[jon1]

Hi Audioguru,

It's me again after a long time, but I want to know what do you use to supply the circuit with current in the +9 adapter? Can't I use a 9 volt battery? Because I don't have any 7.2 volt battery.

Jon

 

[audioguru2]

Hi Jon,
My Sound Level Indicator uses a "9V" rechargable Ni-Cad battery that is really only 7.2V because it has six 1.2V cells. It is almost always fully-charged at 8.5V.
The Ni-Cad battery powers it for about 20 minutes with the brightness control at max (26mA for each LED) and a loud signal so most LEDs are turned on.

My AC-DC adapter is 9VDC/350mA. A 500mA adapter would also work fine.

An ordinary 9V alkaline battery will power it for about 1.5 hours at max brightness with most of the LEDs turned on. The 9V alkaline battery will last for about 62 hours with no sound so that all the LEDs are off.

 

[jon1]

Thanks for the answer, but do you have a bigger and cleaner image of the circuit you used? Because I can't see well on the image you provide on the site.

J.

 

[audioguru2]

Hi Jon,
I am sorry that the picture of my Veroboard layout is hard to see. I have brightened it and hope it is clearer.

 

[jon1]

Thanks for the image, it's a bit better, and now I'm done with the circuit but when I supply it with current every LED lights and there's no sound around! What might be the problem? (And what's the order for the LEDs, is it 10 to 18 on the LM2915 or is it 18 to 10?)

J.

 

[audioguru2]

when I supply it with current every LED lights and there's no sound around!

Did you substitute any parts? The opamps?
Without a signal, pin 5 of the LM3915 should be very close to 0V. The violtage rises as the sound picked up is louder.
Without a signal, pin 6 of the LM3915 should be about 0.47V. Then the 10th LED should light when the voltage on pin 5 is 0.47V or more, and the 1st LED should light when the voltage at pin 5 is 0.015V.

what's the order for the LEDs, is it 10 to 18 on the LM2915 or is it 18 to 10?

The datasheet for the LM3915 shows the order of the LEDs. Pin 1 is the most sensitive LED and pin 10 is the least sensitive.

J.

 

[jon1]

I don't think I substituted any parts. When I plug the battery to the circuit every LED works (even when there's no signal...) except the ones connected to the 10th pin on the LM3915. I looked around and I think it's maybe because of the 3rd pin of the LM3915 connected directly to the +9V, because when I take it off no LED works. The brightness pot and the mode switch works fine, but when I turn the brightness pot to the max some LEDs stop working (even when there's no signal...) I think that there's no current passing after the LEDs and I don't know why...

Thanks,
J.

(Is there any e-mail to contact you, because I have to finish this project fast and you only seems to check this forum twice a day and I really need your help)

 

[audioguru2]

Hi Jon,
Pin 3 of the LM3915 is its positive power supply input. It won't work if it is disconnected.

Measure the DC voltage at pin 5 and at pin 6 of the LM3915 and see if they are what I said in my last post.
Also measure the regulated 5V supply to see if the regulator works properly.

When you turn up the brightness then the battery current becomes 270mA which is too much for some 9V batteries, I think its voltage drops too low with such a high current. Measure tha voltage of your battery with the brightness control at max.

My Ni-Cad battery can supply the high current for about 20 minutes. A brand new 9V alkaline battery should be fine for nearly 1.5 hours.

I don't carry e-mail around with me. I check replies about a few times per day. 

 

[jon1]

Ok I'll check the voltage for the pins. And maybe the problem is in the transistors' connection. Where do I connect  the + of Q1 and Q3, on the +9V or the +5V? And another thing, I connected the LM2931AZ-5.0 on the same line as the LEDs, so do I have to supply it with current with the +9V? The same thing with the 10/1W resistor. I'm going to check it...

(Another question, what does all the red X's on your Veroboard layout means?)

J.

 

[audioguru2]

Where do I connect  the + of Q1 and Q3, on the +9V or the +5V?

The "+" is +9V. The 10 ohm resistor in series with the LEDs, C6, the input of the LM2931, pin 3 of the LM3915, pin 8 of the dual opamp and the collectors of the transistors all connect to +9V.

I connected the LM2931AZ-5.0 on the same line as the LEDs

Then you have shorted the 10 ohm resistor. Connect the 10 ohm resistor in series with the LEDs as shown on the schematic.

what does all the red X's on your Veroboard layout means?

Each red X is where the track is cut with a drill bit. Here is a picture:

 

[jon1]

OK thanks! I'm going to reverify it all! And I'll come back if necessary...

J.

 

[jon1]

Ok now, does that mean that R1, R2, R15 and C3 are connected on the line of the LM2931's output (so the +5V)? If yes then I tried it but it does not work...

J.

 

[audioguru2]

Ok now, does that mean that R1, R2, R15 and C3 are connected on the line of the LM2931's output (so the +5V)? If yes then I tried it but it does not work...

Yes, but also R15 must be connected to +5V or many of the LEDs will light, because then pin 6 of the LM3915 will not have 0.47V but instead it will be 0V.

Please measure the DC voltage on pin 5 and on pin 6 of the LM3915 when there is no sound and report the measurements here.

 

[jon1]

Ok, but I can't measure the voltages now, I'll give them when I'll have them. And the R15 is connected to the +5V but nothing happens.

J.

 

[jon1]

I replaced the dual opamp but it didn't change a thing, one the LEDs works all at once or nothing works and the battery gets hot. I'm still trying to get the voltages...

J.

 

[audioguru2]

If the battery gets hot then something is is drawing too much current.
Did you use an MC33172 dual opamp?
Did you use an LM2931Z-5.0 low-dropout voltage regulator?

 

[jon1]

Yes I used those things but I think the current is not passing through them, that's why maybe all the LEDs are working at the same time.

J.