[MOVED]LM3914 Audio Spectrum Analyzer Project

[elabguy]

Hi, I have made up an Audio Level Meter based on the LM3914 Dot/Bar display driver and it uses the LED-RAINBOW with 10 different colors as the bar graph display. You can cascade a few pieces together to make an audio spectrum display. The audio signal can be connected by the 3.5mm audio jacks and the signal gain can be adjusted by the operational amplifier with a single potentiometer. This module can be powered by a single 5V USB power supply where it can be found from any PC USB port or any USB power transformer. It works perfectly with most computers, mp3 players, mobile phones or any audio devices with a 3.5mm audio plug.

---------- Post added at 08:27 ---------- Previous post was at 08:25 ----------

The schematic and specification can be downloaded at: Elabguy - Electronic Kits for Hobbyists

Video:
YouTube - ElabGuy Audio Level Meter ASD-V1D.wmv
YouTube - ElabGuy Audio Spectrum Analyzer ASD-V1D.wmv

 

[FvM]

A spectrum analyzer should use a better frequency selection than cascading first order low- and high-passes.

 

[elabguy]

A spectrum analyzer should use a better frequency selection than cascading first order low- and high-passes.

Hi, FvM. you are right, I know a RC 2nd order bandpass filter is not good enough for a spectrum analyzer. However, this is just a very simple project for beginner and I am trying to make it simple. Also, due to the limited single power source and buget, I couldn't able to add too much details on this circuit.
I would like to improve the filters design, Do you have any better opAmp filter design that only require 1 positive power source and does not require a DC offset ?

 

[FvM]

No, I don't see how to operate an active filter or AC amplifier on single supply without a DC offset.

To add another comment, the circuit sensitivity is basically limited by placing the rectifier before the amplifier. I would also prefer a logarithmic scale LM3915 for an audio level display.

 

[daver01a]

elabguy...
I am interested in your Spectrum Display (LED level meter) Kits...
Do you have any left?
How much?
..
I think these are perfect birthday gifts for a few friends..
..
Dave
dmason (@) phoenixcomputerlabs (.) com

 

[Audioguru]

The LM3914 or LM3915 are designed to directly drive LEDs with regulated current. But in the circuit there are two 74LS04 ICs driving the LEDs with very low current. Why?

 

[KJ6EAD]

The LM3914 in bar mode can't drive the LEDs at their maximum current so the circuit description includes driver transistors but they are nowhere to be seen on the schematic.

 

[Audioguru]

The LM3914 in bar mode can't drive the LEDs at their maximum current so the circuit description includes driver transistors but they are nowhere to be seen on the schematic.

The LM3914 can have each output at 25mA without getting too hot since the supply voltage is only 5V. But the "rainbow LEDs" are common anode so the active low outputs of the LM3914 cannot drive them. Nothing pulls up the inputs of the 74LS04 LED drivers so their input bias current floats them up to turn off the LEDs. when the outputs of the 74LS04s are high to turn on the LEDs the current is fairly low and the "rainbow LEDs" have series current-limiting resistors anyway.

The "second-order" bandpass filters have a single order for a lowpass and another single order for a highpass.

 

[KJ6EAD]

The LM3914 can have each output at 25mA without getting too hot since the supply voltage is only 5V.

That's right. I'm used to seeing higher supply voltages on these. You're pushing your luck if you run more than 10mA on each LED and they're all on. It's best to keep the total dissipation below 700mW.

 

[elabguy]

elabguy...
I am interested in your Spectrum Display (LED level meter) Kits...
Do you have any left?
How much?
..
I think these are perfect birthday gifts for a few friends..
..
Dave
dmason (@) phoenixcomputerlabs (.) com

Hi Dave, I messaged you already, have you receive my email at all??

---------- Post added at 05:51 ---------- Previous post was at 05:48 ----------

Thx Audioguru !

One of the reason that I made up this Audio Spectrum Analyzer project is to demonstrate an example of using the LED-Rainbow.

---------- Post added at 05:52 ---------- Previous post was at 05:51 ----------

Thx Audioguru !

One of the reason that I made up this Audio Spectrum Analyzer project is to demonstrate an example of using the LED-Rainbow.

---------- Post added at 05:53 ---------- Previous post was at 05:52 ----------

The LM3914 can have each output at 25mA without getting too hot since the supply voltage is only 5V. But the "rainbow LEDs" are common anode so the active low outputs of the LM3914 cannot drive them. Nothing pulls up the inputs of the 74LS04 LED drivers so their input bias current floats them up to turn off the LEDs. when the outputs of the 74LS04s are high to turn on the LEDs the current is fairly low and the "rainbow LEDs" have series current-limiting resistors anyway.

The "second-order" bandpass filters have a single order for a lowpass and another single order for a highpass.

Thx Audioguru !

One of the reason that I made up this Audio Spectrum Analyzer project is to demonstrate an example of using the LED-Rainbow.

 

[ibitechs2005]

Please, give us the circuit diagram in the post.

 

[Audioguru]

Please, give us the circuit diagram in the post.

A link to the project is in the first post of this thread. It is a very clear PDF file type that can be zoomed.
Here is the schematic from the link: