Audio Spectrum Analyzer Step #2

      This is a follow-up post on building audio spectrum analyzer. 

    In previous post I created circuit that could show audio spectrum on one 10 segment led bargraph display. Also in previous post I encountered problem with signal strength, so I have to implement solution on adjusting audio signal level.

    But before creating amplifier, I decided that I should stack up another led bargraph, so i would have 20 led segments in a row.

     This way I will have bigger range to test audio amplifier performance.

     The fundamentals of getting it done is wiring two LM3914 IC so that they would work "hand-in-hand". I.e. when signal is 0, both LED bargraphs should be blank (not lit), when signal is to the max, both LED bargraphs should be lit fully.

     While searching through the Internet, I saw different versions of combining these IC, but believe it or not, the best diagram can be found in official LM3914 datasheet. :)

      I recreated the diagram so it would be a bit more understandable taking out mode switch and rearranging LM3914 IC placement in original scheme. 

This is what I got:

   

Using this scheme, I created circuit on a breadboard:  

Don't pay attention to the resistor across the led bargraph. I rearranged it afterwards.

And this is the video of what I got:

      As you can see, signal from computer is only strong enough to light only one LED bar graph. So next step will be signal amplifier implementation. 

      At this point I was wondering, is the second bar graph actually working or is there a problem in my circuit. But when I disconnect audio jack, both led bargraphs light up. This is a good sign as I can see, that both ledbars are working. But, I will have to find out, why is it lighting up when I disconnect signal and how to prevent it. 

 

Problems: 

1. Implement pot to adjust LED brightness.

2. Implement audio signal amplifier.

3. Find out why both led bargraphs are lit when audio jack connector is disconnected and how to prevent it.
4. I should order few LM3916 ICs and try them instead of LM3914 as they are more suitable for audio signal metering.

Audio Spectrum Analyzer Step #1

     Some time ago I decided that I want audio spectrum analyzer in my car. Not for any practical reasons. Just BECAUSE I CAN. :D Well, the idea started as a rotating center console with iPhone attached to it, which should display live audio spectrum using microphone as an input signal.

     I got far with that project, as you can see in this blog (read "Motorized gadget"), but unfortunately I encountered some major problems.

     1. iPhone was a bit too big for the space in which it should rotate. When the console is being inserted in car, it has less space than it is while console is on my table. So iPhone gets stuck.

     2. Microphone is a bad way to "capture" input signal. Every microphone and every speaker has its audio range which it can sense and play. So microphone couldn't display/analyze audio spectrum precisely. And I didn't want to mess with iPhone's electronics and OS/apps.

     Although previous project is unfinished (and it seems that it will stay that way) I still wanted to integrate audio spectrum analyzer in my car.

     You can buy already pre-assambled kits, but hey - building it on my own sounds more exciting and interesting.

So here it goes.

     Since I'm an IT specialist with some background in programming I'm used to develop programs building one small module, then test it. Then build next module and integrate it with previous. And again - test it. So this project will be held similar.

     I started by creating one LED bar graph which would work as an audio spectrum analyzer.

     Started by reading some tutorials, gathering information and buying electronic stuff.

     The most fundamental part of this schematics is dot/bar display driver integrated circuit (IC) LM3914.

     There are three IC types in the LM39 group. Although LM3916 would be more suitable for this project, as it is working better with audio signals, I bought LM3914.

Schematics are pretty much the same for all LM39 IC, so I used the following schematics:

Scheme taken from: CircuitsOnline.net

The parts needed for this are:
IC = LM3914 or LM3915 or LM3916
R1 = 1k Ohm
LED = led bar graph (I used Kingbright. You can use seperate LEDs, but then resistor for each LED must be applied)
C1 = 2.2uF 50V (electrolytic)

In this scheme on the pin5 audio signal must be applied.
My input voltage ~9 V.

This is how it looks on breadboard:

This is the video:

PROBLEM:

     1. Input signal from computer is ok. Input signal taken from phone is too weak. Signal amplification is needed and also possibility to adjust signal gain with potentiometer.

NEXT STEPS:

     1. Signal amplification with Low Voltage Audio Power Amplifier IC (LM386) and potentiometer for signal gain adjustment.