another question about a audio spectrum analyzer

[bountyhunter]

bounty hunter - i see. This is more of an "eye candy" project, and i don't want to modify it too much, so i'll stick with what i have

2 more questions (hopefully)

In the driver section, there are 10 PNP transistors, which look like are used for switching on the LEDs. The document does not specify what kind of transistors to use, but it looks like i could use a simple switch transistor. Would something like a 2n3906 do?

That's what I always use.

Also, its a bit difficult to find caps that are 160pf and 620pf that aren't either surface mount or sold in packages in 1000 (yikes!). Could i use a more common value thats + or - 50pf without throwing off the filter too much?

I think you could.

 

[MrDEB]

thats the issue I have about digikey

have to buy a bunch
look at mouser they have lots of 160pf and 620pf caps
160pf capacitors
620pf capacitors
simple transistors = yes 2n2222 etc.
the peak detector section is from the data sheet for the lm3916

 

[kchriste]

bounty hunter - i see. This is more of an "eye candy" project, and i don't want to modify it too much, so i'll stick with what i have

For eye candy, I would choose the logarithmic LM3915 over the linear LM3914 because it is less likely to be pegged to the max during loud passages or doing nothing during the quiet part of the music.

Would something like a 2n3906 do?

A PN2907A would be better since it can handle more current than the 2N3906 which is only good to 100ma or 200ma depending on the manufacturer. The PN2907A will handle the peak 200ma required with ease. I would use a lower base resistor of 1K for the PNP drivers since the 10K will only supply a little over 1ma. (Page 23)

 

[MrDEB]

the transistor that is refered to

doesn't carry a-lot of current as its only used for a peak detector circuit.

 

[kchriste]

We are obviously looking at two different schematics. I'm looking at page 23 of this one:
https://www.electro-tech-online.com/attachments/audio-spectrum-analyzer-en-pdf.15065/
Agreed. A 2N3906 will be a good sub for the BC558 in the circuit you posted above.

 

[homik]

Well, i've been going over the parts and LEDs are expensive! i'd pay 25$ for a 10x10 display :/ and with MrDEB's schematics i'd need 10x lm3916 (due to a brightness issue)

What would be the practicality of me making a small LCD display? I ask because that would most likely require a microcontroller and i have no programming background. But from what i u understand i'd need a analog to digital converter, a microcontroller/display driver, and an LCD.

 

[birdman0_o]

100 Leds on ebay is about 13$ with free shipping.
What brightness issue?

 

[homik]

MrDEB mentioned (not in this thread?) that if you multiplex 100x LEDs then the will be dim since they are on 1/10th of the time.

maybe 100x regular LEDs are ~$13 but i was thinking about getting those LED bargraph arrays, which are a bit pricey :S

 

[birdman0_o]

Ah, why would you use those, 5mm leds are much bigger and bar graphs ones are only 1$ each about x 10...

Yes it will be a bit dimmer, however you can use super bright Led's and you will barely be able to tell. You can even bump the current past 20mA as they won't be on all the time and will have a bit of time to cool down!

 

[homik]

You can even bump the current past 20mA as they won't be on all the time and will have a bit of time to cool down!

Hmmmm, good point. Well, i still don't have my display section fully designed, so i can try that

 

[audioguru]

Ultra-bright LEDs sold on E-Bay are cheap dim Chinese ones with a lens that focusses the beam into a narrow angle that cannot be seen a few degrees off-axis.

Multiplexed LEDs need 10 times the normal current to be seen brightly.

 

[MrDEB]

found lots of drivers

LM3914 = $1.29each Allied Electronics - Electronic Components Distribution
LM3915 = $1.96 each The Electronic Goldmine
LM3916 $2.64 each DigiKey Corp. | Electronic Components Distributor | United States Home Page
LM3916 $2.64 each DigiKey Corp. | Electronic Components Distributor | United States Home Page
I think you will find that going with seperate drivers will be easier and cheaper.
Look on Ebay for LEDs SMD would be easy. We purchased from victory or ?? so Chinese company.get 50 for few $'s
lots cheaper than buying here but not as good of quality but you pay for what you get.
I wish the SMD we bought were brighter.
in the files I sent you I have the SMD display boards using SMD.have the displays wired mirror so the LEDs progress from the middle to the outside. Case is supposed to be a 6 sided box with the displays on two front pannels w/ a middle pannel w/ contols for volume.
the bandpass controls under each display.
using red, green, yellow LEDs.
plans are to use some bright blue LEDs to light a halo around each knob.
hope this helps

 

[kchriste]

What would be the practicality of me making a small LCD display? I ask because that would most likely require a microcontroller and i have no programming background.

Yes, you can do it all with a dsPIC and LCD:
https://www.electro-tech-online.com/threads/dspic-glcd-spectrum-analyzer-d.85530/
But you need programming experience and a programmer for the PIC which is a whole other kettle of fish.
If you want to learn analog electronics, the method you've chosen is a good one. If you wanted the learn microcontrollers and programming then the dsPIC and FFT is too high of a level to start at for a beginner. Besides, LEDs are much prettier!

 

[MrDEB]

ouooo the colors!!

give me more

 

[MrDEB]

spectrum analizer pwr supply revisions

after it was pointed out that my power supply fore the graphic equalizer/spectrum analyzer was inadequat I made some revisions that should supply more than enought current.
just need to make pcb revisions to accommodate the J7 and J8 plugs
note this schematic was designed over numerous posts last year so hopfully the display design is correct. Should be.
there are ten of these displays (only one is pictured)

 

[audioguru]

A huge 2N3055 power transistor is good for 10A. You have three in parallel so your load is 30A??

The 2N3055 transistors are all emitter-followers so their output voltage is about +7.5V. Emitter-followers do not need a resistor in series with the base. The transistors that are in parallel need a resistor in series with each emitter to balance their Vbe. But you don't need three 2N3055 transistors driven by another one.

 

[Nigel Goodwin]

A huge 2N3055 power transistor is good for 10A. You have three in parallel so your load is 30A??

With a 1A transformer, and 1A rectifiers.

 

[MrDEB]

forgot to change transformer

only need to drive 100 LEDs (ten 3916 displays)
idea for upping supply current
High Current Voltage Regulation - Electric Circuit
yes only need 3-5 amps so I overkilled the requirement.

 

[audioguru]

You need only a single 2N3055 transistor without the 1 ohm base resistors and without the five 2200uf capacitors. The LM7809 that drives it needs a 10uF output capacitor. Add a 100uf capacitor to the output (the emitter) of the 2N3055.

 

[MrDEB]

Revised power supply as per suggestions

the plugs for the two seperate display boards have caps as I believe tis is common practice for off board connections? 2200uf might be too big??, thinking 100uf??
the resistor R5 is still in place as per link.
High Current Voltage Regulation - Electric Circuit
may not be correct??
a question I have is on the display boards it was suggested looong time ago to use a 15 ohm resistor for brightness due to multiplexing.
I assume the 3916 is multiplexing??