First Electronic project - Sound level displayer

[kidi3]

I trying to build a sound bar, which uses the output of an mic, to indicate the sound level in a room.

This is my first Electronic project, so I hope you would bear that mind, before you respond.

My diagram look like this

https://snag.gy/wxmIt.jpg

My idea is to use Comparators, and use it to compare it with a ref. voltage set by me, and thereby visualy show the sound level, with the diodes.
I haven't put any values for my resistor, since I haven't choosen the mic i am going to use.


As for Voltage source I was thinking of using Batteries, which using as many diodes as i am doing will end up being alot. I calculated that i min. should use around 50 V, if i Used resistors with 1 ohm. but could this be done more effeciently???

Ground is another thing that bothers me.. I don't know i should implement it in my PCB?

I haven't choosen a Mic yet, anyone you would recommend?

And using the diagram i've drawen, would it even be possible build a circuit that iam looking for,have I made any mistake, or could something have been done more effeciently?

Thanks in advance
// Kidi3

 

[Audioguru]

An LM3915 IC has 10 comparators connected to a resistor ladder and the 10 outputs have their output currents set with one resistor. There is an accurate adjustable voltage reference. It can make a moving dot with one LED lighted or a bar of lighted LEDs. Use an electret mic.

Your circuit is completely wrong because it does not have a resistor ladder and it has no preamp to boost the tiny level from the mic 100 to 500 times.
An output of an LM339 is the collector of an NPN transistor that can sink (go to ground) but it cannot source (go up and turn on your LEDs).
The outputs of the LM3915 IC sink to ground and can drive your LEDs.
Why do you have so many LEDs? You need only one LED for each comparator.

My Sound Level Indicator project uses an electret mic, a dual opamp as a preamp and peak detector, two transistors in the peak detector, an LM3915 IC and a rechargeable 9V battery that is used only to demonstrate it away from its 9VDC wall-wart/charger. I used two LEDs per output so it looks like stereo but it is simply mono instead. I added a 3rd transistor to increase the gain 10 times when sound levels are low so it has a range of 50dB.
I used stripboard instead of a pcb. The strips of copper form half of a pcb and the parts and a few jumper wires form the other half.
It is 8 years old and still works perfectly. Its original 9V Ni-Cad battery failed and was replaced by a 9V Ni-MH battery.

 

[kidi3]

Thanks for your response.

The reason why i choose to use that many LED's is because it is a design requirement. So I can't do anything about that.
You are absolutely right about the comparator and the fact that i need a pull - up to make it give an output.
1 comparator = 1 Array of LED.
The reason why i haven't added the MIC is because i haven't found one, but my intention was to boost the output, since those tiny voltages aren't operable.

But i don't understand where you want me to use a R - 2R network??.. Why can't i use my comparator solution??

 

[Audioguru]

Don't you want each comparator to light its LEDs at increasing input levels?
The resistor ladder in the LM3914 is linear. Each comparator is triggered at an increase in level of 1/10th.
The resistor ladder in the LM3915 is logarithmic like your hearing's sensitivity to loudness. Each step is 3dB.
Didn't you look at the schematic of the LM3915 in its datasheet and see the levels that trigger its comparators?

 

[kidi3]

Don't you want each comparator to light its LEDs at increasing input levels?
The resistor ladder in the LM3914 is linear. Each comparator is triggered at an increase in level of 1/10th.
The resistor ladder in the LM3915 is logarithmic like your hearing's sensitivity to loudness. Each step is 3dB.
Didn't you look at the schematic of the LM3915 in its datasheet and see the levels that trigger its comparators?

I being a bit unsure on how you want me to add the "resisitor ladder", How would i be able to add something to its internals??

LM3915, seesm to look like what i am searching for, would one be enough to power all the LED, or should i more, and if so how many???

 

[Audioguru]

Why don't you download the detailed datasheet for the LM3915? It has 10 outputs but maybe you need 12 outputs. Many years ago I made a project with 20 outputs.
The datasheet shows output currents over 25mA. My project has maximum current of 26mA but people complained it was too bright so I added a dimmer switch to reduce the current. Your LEDs are in series so their current is the same an one LED.

 

[kidi3]

It looks like I don't have LM3915, but i have an LM3914n-1.. Now i just need to find the mic..

 

[Audioguru]

An LM3914 has linear steps, 1V, 2V, 3V, 4V etc. But sound levels are heard logarithmically, not linearly. The LM3915 has logarithmic steps 3dB apart which is half or double the power which is a small difference in loudness.

If you use an LM3914 then a loud sound lights all 10 LEDs (or the 10th LED), a sound level a little less lights 7 LEDs (or the 7th LED) and a sound level a little less lights 5 LEDs (or the 5th LED) etc. The first LED lights at a fairly loud sound level.
If you use an LM3915 then a loud sound lights all 10 LEDs (or the 10th LED), a sound level a little less lights 9 LEDs (or the 9th LED) and a sound level a little less lights 8 LEDs (or the 8th LED) etc. The first LED lights at a low sound level.

Why can't you buy an LM3915? It is common and inexpensive.