• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Real new guy here! Need some help with simple LED circuits.

Status
Not open for further replies.

adamd91

New Member
Let me start off by saying Hello!! I have just gotten into messing with electronics. I realized this is a skill I have to develop because I am a guitar player who is sick of paying for repairs and modifications.

To kind of get myself started, I've designed a project for myself. I want to install LED lights into my guitar, so that as I play, they play along with me. I pick/strum, they light up. This is a very cool effect. Here is a perfect example of what I want to do. YouTube - My Custom LED Guitar - One of a kind!

I have been able to find schematics. I've been able to create them to the point of working. However, they aren't working properly.

I think I'm having trouble because I don't know what to use. I know I want 8 blue LED's. But I don't know what resistors to get or what kind of power supply to use (obviously a battery, I just don't know what will work). Any, and I mean ANY help will be appreciated.

This is one of those things where I'm confused now, but after I do it, things will make much more sense.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
If you choose say a 12V battery and Blue LED's [ which have a forward voltage drop of 3V to 3.5V], you could connect three Blue LED's in series.
For an LED current of say 15mA, you would need to drop approx 3V across a series resistor.
Using Ohms law, thats 3V/0.015 = 200R series resistor [use a 180R]. In order to drive a greater number of LED's, make up the required number of 3 LED and 180R strings.

OK.?
 

SABorn

New Member
It would be wise to post the schematic of the circuit you are building on the forum here so we can see what is needed to operate things fully.

Eric is correct but it is a little confusing how he explained it.

Lets look at ohms law for just 1 blue led and a 9 volt battery as it is more likely what you will use compared to a 12 volt battery.,

1 blue led operating voltage of 3 volts at 20 milliamps. (0.020 amp)

9 volts - 3 volts = 6 volts

6 / 0.020 = 300

So you would use a resistor around 300 ohm, nearest most common resistor would be 330 ohm resistor

Pete.
 

audioguru

Well-Known Member
Most Helpful Member
You need an electronic circuit to drive the LEDs. Something like an audio amplifier IC modified so its output is DC, not a sound signal.
The other guys mentioned how to connect an LED to a current-limiting resistor and battery so the LED lights continuously.
 

ericgibbs

Well-Known Member
Most Helpful Member
You need an electronic circuit to drive the LEDs. Something like an audio amplifier IC modified so its output is DC, not a sound signal.
The other guys mentioned how to connect an LED to a current-limiting resistor and battery so the LED lights continuously.
As I read the OP's post, he has a working circuit, its the Blue LED's that his problem.

I have been able to find schematics. I've been able to create them to the point of working. However, they aren't working properly.
I think I'm having trouble because I don't know what to use. I know I want 8 blue LED's. But I don't know what resistors to get or what kind of power supply to use (obviously a battery, I just don't know what will work). Any, and I mean ANY help will be appreciated.
 

audioguru

Well-Known Member
Most Helpful Member
However, they aren't working properly.
It must be a secret because we are not being told what is not working properly.
Are the LEDs not lighted bright enough?
When the schematic of the audio to LED-current circuit is posted then we can see what is wrong with it.
 

adamd91

New Member
My Reply

I'm sorry, as a new member, I guess my replies must be approved by a moderater and aren't showing up. But here's the link to the schematic" Optional extra features.
I have the LM386. The LED is lighting up now, but when I strum the guitar, the light gets dimmer.

UPDATE: I have the LED working so that it comes on when I strum. However, it's so dim that it's barely visible. The 9volt is at full, and I'm not using a resistor in the circuit. If it burns out, then at least I know that it works.

Sorry about the lack of responding, I have no Idea what is going on with this page.
 

audioguru

Well-Known Member
Most Helpful Member
The circuit you found is garbage.
It is missing all the important parts shown on the datasheet of the LM386 amplifier IC. It is also lighting the LEDs all the time.
The LEDs might dim a little if the amplifier is overdriven.
The circuit loads down the guitar pickup which makes it sound weaker and different.
There is nothing to limit the current in the LEDs so they will burn out soon.
Most Intructables are designed by people who know NOTHING about electronics.

I would use a Jfet input so that the guitar pickup is not loaded down.
Then I would DC bias the input of the amp so that the LEDs are turned off.
Of course I would use current-limiting resistors in series with each LED or wire a couple or a few LEDs in series and in series with a current-limiting resistor.
Then the LEDs will be off when the guitar is not playing, they will be dim when the guitar sound is not loud and will be bright when the guitar is loud. You will see the LEDs dim slowly when the guitar stops being played.
 
Scrooge, Maybe ya should post a schematic for em. I'd like to see it too. Are the blue led's super brites ? did he ever mention the size ? not that it matters just curious.
 
im just an electrician so im new myself, these guys are the real pro's but i wonder if this would work ? it would need 2 conductors tho ? would it work fellas ? i forgot a resistor ahead of the transistor.
 

Attachments

Last edited:

adamd91

New Member
Scrooge: Wow, in just 4 sentences you were able to show me why it was crap! Haha. You managed to explain both of the things that are happening to me, without even being here. So, the Jfet. Would you be able to post a schematic as Jim said? And how would I "DC bias" the input? This is all very new to me. What would you recommend in the way of LED sizes? Or power supply for that matter. Also, would the Rat Shack have the Jfet?

The LEDs I'm using are titled "Ultra High Brightness 10mm Red LED."
 

audioguru

Well-Known Member
Most Helpful Member
Here is a Jfet preamp for a guitar pickup. It doesd not load down the pickup so the sound is fine. this preamp can feed your power amplifier and it can feed the LM386 that drives the lEDs.

The datasheet for the LM386 shows a 0.05uF capacitor (today a 0.047uF capacitor is used) at its output in series with a 10 ohms resistor to ground to prevent oscillation.

The (-) pin 2 input of the LM386 can be biased to a small positive voltage with a voltage divider to cause its DC output to drop and turn off the LEDs when there is no signal. A signal will cause the LEDs to light with the brightness depending on the loudness of the signal.

Ultra High Brightness LEDs are cheap dim ones in a case that focusses the beam into a narrow angle so it appears very bright if it is shining directly at you. Good bright LEDs have a bright wide-angle beam.
 

Attachments

adamd91

New Member
So according to this, the signal input and signal ground would connect to the guitar output jack? Correct? The signal input would go to the J201, the outside pins, and the output and ground would go directly to the LM386?

Just to clarify, this is for LED's that are placed in the actual guitar. You mentioned power amplifier. You're talking about a component/ LM386, and not the actually amplifier that makes sound, correct?

Thank you for taking the time to help me with this!
 

audioguru

Well-Known Member
Most Helpful Member
So according to this, the signal input and signal ground would connect to the guitar output jack? Correct?
No. The guitar's pickup feeds only the input and ground of the Jfet preamp circuit.
The output and ground of the Jfet preamp circuit feed the output jack and also feeds the input of the LM386 LED driver circuit.

The signal input would go to the J201, the outside pins, and the output and ground would go directly to the LM386?
I don't know which connectors you have so I don't know what are the "outside pins".
Many different Jfets can be used in that simple circuit. Its output connects to your power amplifier using a shielded audio cable. Its output also connects to the input of the LM386 amplifier with shielded audio cable. Connect all the shields together and to the circuit's ground.

Just to clarify, this is for LED's that are placed in the actual guitar. You mentioned power amplifier. You're talking about a component/ LM386, and not the actually amplifier that makes sound, correct?
You will have this Jfet preamp and the LM386 LED driver inside the guitar. They need to be powered. A 9V battery can power the Jfet preamp and a second 9V battery can power the LM386 LED driver. The LEDs will dim then the battery for the LM386 LED driver will die first but your guitar will still play.
 

audioguru

Well-Known Member
Most Helpful Member
whats wrong with my idea ? its simple.
What idea?
To have the guitar pickup connected directly to the output jack? Then the capacitance of the cable to your power amp affects the sound of the guitar and the sound will be different for each different type and different length of cable.

When the Jfet preamp drives the output cable then there is almost no affect from the cable.
 
so your saying the sound would change from that little bit of current caused from a transistors base ? well, ok im not being a smart alleck i wouldnt of thought of that. i put sensors on my drums for the same thing he's doing (snare and bass) they triggered mosfets. i know a drum isnt connected for amplification and my purpose was served but im not a guitar player either.
 

audioguru

Well-Known Member
Most Helpful Member
so your saying the sound would change from that little bit of current caused from a transistors base?
There is no transistor, instead there is an LM386 power amp that has an input restance of 50k ohms and it needs a resistor to ground.

Look at the schematic of the Guitar preamp. It was written by a guitar expert who says that 1M ohms load is the minimal acceptable load that should be used.

i put sensors on my drums for the same thing he's doing (snare and bass) they triggered mosfets. i know a drum isnt connected for amplification and my purpose was served but im not a guitar player either.
Drums are 1000 times louder than a guitar so a sensor produces a whopping high output signal which is high enough to turn on a Mosfet.
 
Last edited:

gtr_stitch

New Member
Hey AudioGuru...
It's a little crude and I'm sure some things (or a lot) could be and probably should be changed, but would something like this pic do the trick?
I play guitar and actually have some holes drilled in mine. when i first got into circuits, my first project was a 555 circuit. i thought it would be supremely cool to put some blinking lights in there. but they only blinked. it was so lame.
anyways, i would love to give a purpose to those little empty spaces...
 

Attachments

Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top