Hello everyon, I am a new member here, and this is my first post. I have always been interested in electronics, and I have done several guitar wiring projects with some simple as well as moderately hard wiring schematics, all of the info I needed for those projects was readily available on the internet, however, not so much for this project!

This project has got me pretty stumped. The idea is to install some RGB LED's in my bass. im thinking 2 LED's by the pickups, and 2 by the bridge. I want to be able to control the mixture of red, green, and blue in order to achieve any color I want. My though process is to use potentiometers to adjust the input voltage to the LED's. I am not sure what would be better as far as series or parallel wiring, so input on that would help.

Another cool factor that I thought of doing is using an NPN transistor as a "Switch" to operate the lights using the output from the bass pickups to the Base lead of the transistor. This would be operated by using an on/off/on switch. One "on" position would bypass the transistor circuit and allow the LED's light up continuously, for mixing the colors, as well as a "steady on" feature. the other "on" position would engage the transistor circuit so that the LED's light up only when the strings are plucked. One thing i do understand is that an NPN uses a positive voltage applied to the Base lead to operate the switch. Being that the output of the pickups is an alternating current, it makes sense to me that this would make the lights flicker at the same frequency of the note being played. I also would like to know if this would introduce any signal loss or noise into the output of the bass when it is plugged into the amplifier. The pickups that I will be using are Seymour Duncan Quarter Pound P-Bass pickups. They are supposed to be quite hot in there output. I am really hoping to get at least 5mA out of them in order to operate the transistor.


I am including a mock-up shematic of what I think this looks like on paper. Keep in mind that I do have 3 separate rows of LED's because I know that I will need a separate circuit for each individual color. The LED's Red1, Green1, and Blue1, are infact inside one LED. The same goes for the rest of them. It just made more sense in my head to plot it out this way. Also, I am not attached to any of the values listed for any of the resistors, potentiometers, or the transistor. In fact, that is the main purpose of this post. I have no idea what values I should be looking for. The LED's im looking at are rated as follows:

The forward voltage is 2v for the red, and 3v for the green and blue.
Current is 20mA

The battery of choice at the moment is a CR123a lithium at 3.2v, but if somthing else is prefered, that is okay as well.

Im excited for your input! thank you!!

 

Correction. I'm hoping for 5mV not 5mA to be available from the pickups!

 

Welcome to AAC!
Unfortunately, driving LEDs from a guitar pickup in a pleasing way is going to be less straightforward than you would like.
Because a pickup needs to work into a high impedance to preserve its frequency response, simply attaching a LED or NPN transistor base to it would apply a low impedance and hence mess up that response. A buffer amplifier stage would be needed. Additionally, some form of peak-hold circuit would likely be desirable, so that a LED flash would last long enough to be visible.
I suggest you do some googling for "color organ" to see the sort of circuits usually used for driving LEDs in synchronism with music, particularly if you want LED colour to be varied automatically in dependence on note pitch.

 

To turn on a transistor you need to supply its collector current when on, Ic,
by 10. Ie. Ibase = Ic / 10. You also need to limit its current otherwise it
will self destruct. So a simple R in series into the base will suffice. Its
value is R ~= (Vsignal - Vbe) / (.1 x Ic). So in your case Vbe ~= .7V,
Ic / 10 = 20 mA / 10 = 2 mA.

To do the brightness control your R in series with pot should limit max current
allowed. So R = (3.2 - Vf) / 20 mA, Vf = LED forward voltage. The pot then
should be calculated to limit current ~ 1 uA when you want fully off. You will
have to experiment with that.

I see you are contemplating using a coin cell for power. For the number of
LEDs I think that cell would last minutes, if that. You should think more like
a LiPo pack or less desirable some alkaline cells, C or D.

A more efficient way, longer battery life way of doing this is to use PWM switching
modules. You might look at alliexpress.com or banggood.com for these modules.
They are typically cheap, simple to use. Boost or Buck modules, all leds of a specifc
color in series, that way light output of each led will have same current, helps to
match their brightness better. Paralleling them like you are doing, because of
electrical differences LED to LED, will have one LED hogging more of the current,
starving the others.

Boost (step up) if you want to use low V battery pack, Buck (step down) if you use
a higher V adapter like a Laptop brick.

Here is an example buck

https://www.banggood.com/3Pcs-LED-D...-p-1140978.html?rmmds=search&cur_warehouse=CN

Here is a generalized discussion, google "basic led drive": to get other references.

http://www.lightingdesignlab.com/sites/default/files/pdf/Basics of LEDs.pdf


Regards, Dana.

 

Lookup digital Vu meter project.

Been a long time since I have messed with guitars but doesn't each string have its own unique range of frequencies? Are there any overlaps when you move your finger on the beck for each fstring?

If there are no overlaps then you could build a crude spectrum analyzer. Tou would be able to tell what string was plucked. That would be a cool project. Bet something like that exists too.

 

To turn on a transistor you need to supply its collector current when on, Ic,
by 10. Ie. Ibase = Ic / 10. You also need to limit its current otherwise it
will self destruct. So a simple R in series into the base will suffice. Its
value is R ~= (Vsignal - Vbe) / (.1 x Ic). So in your case Vbe ~= .7V,
Ic / 10 = 20 mA / 10 = 2 mA.

To do the brightness control your R in series with pot should limit max current
allowed. So R = (3.2 - Vf) / 20 mA, Vf = LED forward voltage. The pot then
should be calculated to limit current ~ 1 uA when you want fully off. You will
have to experiment with that.

I see you are contemplating using a coin cell for power. For the number of
LEDs I think that cell would last minutes, if that. You should think more like
a LiPo pack or less desirable some alkaline cells, C or D.

A more efficient way, longer battery life way of doing this is to use PWM switching
modules. You might look at alliexpress.com or banggood.com for these modules.
They are typically cheap, simple to use. Boost or Buck modules, all leds of a specifc
color in series, that way light output of each led will have same current, helps to
match their brightness better. Paralleling them like you are doing, because of
electrical differences LED to LED, will have one LED hogging more of the current,
starving the others.

Boost (step up) if you want to use low V battery pack, Buck (step down) if you use
a higher V adapter like a Laptop brick.

Here is an example buck

https://www.banggood.com/3Pcs-LED-D...-p-1140978.html?rmmds=search&cur_warehouse=CN

Here is a generalized discussion, google "basic led drive": to get other references.

http://www.lightingdesignlab.com/sites/default/files/pdf/Basics of LEDs.pdf


Regards, Dana.

Hi

Using any kind of switching controller/regulator is going to generate a lot of noise and be picked up by the guitar preamp or amplifier.
Just setting a smart phone on top of an amplifier generates noise in the amp.

eT