Basic LED Radio/audio Spectrum Display

[martij7au]

I am working on a project for my electrical engineering lab class, and am interested in learning how to build a led spectrum display. I'm looking at very basic. I want 3 sets of LEDs, one for the high, one for the mid-range, and then one more for the low. Any clues where i can find a design or schematic? any help would be appreciated.

 

[Averagesupernova]

Hmmmm. Engineering project means YOU design it and not copy a schematic from somewhere else.

 

[martij7au]

ok...

Yes, well, in that case, can someone describe to me a way in which to display the signal on the LEDs? I can create the high and low pass filters... I was just curious if there are resources that I can use to figure it out.

 

[Averagesupernova]

Not sure what you current level of training is. If you need something explained to you that you haven't covered in class then I would suggest a different project.

In basic terms though, the signal path would go:

Filter, peak detector or peak to peak detector, comparator, output circuit.

 

[martij7au]

well, i understand the basics... I've completed a circuits analysis class, linear signals and systems, digital electronics and others, and I am currently in a random signals class, power systems analysis, analog electronics, emag, and this radio lab. See, the main project is to build a radio from a kit... and the secondary project, with a partner, is more specialized. only one group from each lab can do a certain project. Some involve solar power, wind-up power, signal strength, and the only one left for our group was the spectrum display, which our professor admitted that hadn't been tried before, so I'm just trying to figure out something. Could you give me a general overview?

 

[martij7au]

could you explain perhaps the purpose for each circuit? I understand the filters to separate the different frequencies, but not the rest

 

[martij7au]

also a fairly important feature would be low-cost.

 

[Averagesupernova]

Hmmmm. I had guessed you would have a handle on the purpose of each block. So I assume that the each band has a number of LEDs? Say like 5 LEDs for for each band? The higher the amplitude of a particular frequency the more LEDs for that particular band light up?

 

[martij7au]

yes, and yes. i understand the filters, i plan on using active filters with op-amps probably... and for the output i figured leds and resistors... but other than that, I am not really sure.

 

[martij7au]

i figured i could use pspice to figure out some of the value details.

 

[Averagesupernova]

Ok. You need to make a varying DC voltage (in each band) that varies with the strength of the particular group of frequencies. This is done with the peak to peak detector and maybe a bit of low pass filtering. From there you need a comparator for each LED. Each comparator will trip at a different level. Making sense?

 

[Daniel3]

This message is for averagesupernova or whoever would care to elaborate on some points he made. I actually have been working on a project very similar to what you were outlining for martij7au. I have constructed several different filters for a range of frequencies from 0-20 kHz. I am attempting to take the output from the bandpass filter and connect to a sequentially lighting LED circuit with 5 LED lights at the moment. This circuit operates just as you described it and as the magnitude of the input signal to the LED circuit increases the LED lights turn on in sequence. (as opposed to simlutaneosly) Now the two components function properly when separate; my first bandpass filter reaches cutoff at 300Hz and 2kHz and the LED circuit also turns on as I increase the voltage; however, they do not function together. I am not sure but it sounds like I am running into the same problem you were describing. I believe I need to construct some type of sampling circuit in order for the two circuits to function properly and I was hoping you could point me in the direction of some help in designing a sampler. Any notes or lectures would be greatly appreciated.