Page 1 of 3
#1
So I've really been thinking of this LED's running off of guitar signal thing for a while, I was thinking maybe putting a solenoid in the signal path and then having a 9 volt battery on the larger terminals. The only problem I can see with this right now is that the power from a pickup might not be enough to trigger a solenoid. Then I was thinking I might be able to use a relay to do it, which I think might be the most efficient way. Then I also thought I might do a buffered two way split into a small boost circuit into the 9 volts which also seems like it's a way to go.

I'm thinking if I can find a relay or solenoid to trigger on pickup output it would be ideal, but I don't really think that it's a practical solution just due to how hard it'd be to find. but then I think a small boost circuit again would be a good way to remedy this. But I haven't the slightest clue on how to make a boost circuit that can trigger a relay.

Anyone willing to lend a hand into this project in any way would be greatly appreciated.
Quote by R45VT
Bastards.
#2
I think the buffered 2-way split idea would work a lot better than using a solenoid. I don't think you want to start messing around with electromechanical devices in your guitar.

I don't see why you couldn't just split the signal into 2 and send them through 2 9-V buffer amps to run your guitar output and LEDs respectively? Otherwise, there would always be the option of putting in another pickup just to run through a single amp to power the LEDs if you're worried about the effect on your guitar tone.
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
Last edited by eddiehimself at Mar 3, 2013,
#3
You can run an LED with a 9v and an op amp using the pickup signal as the trigger to light the LED.

Op-amp because they are very high input impedance, as you don't want to load your pickups into trying to activate a LED. You want the pickup signal to continue to the amplifier in its true form.

Where you planning on locating the LED? And do you want it just to flash on/off, or adjust in brightness?
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 3, 2013,
#4
Quote by Phoenix V
You can run an LED with a 9v and an op amp using the pickup signal as the trigger to light the LED.

Op-amp because they are very high input impedance, as you don't want to load your pickups into trying to activate a LED. You want the pickup signal to continue to the amplifier in its true form.

Where you planning on locating the LED? And do you want it just to flash on/off, or adjust in brightness?

Just flash, however I haven't the slightest clue on how to wire an op amp.
Quote by R45VT
Bastards.
#5
Definitely don't think you want the pure signal from the pickups passing through the LED to the amp, it may clip the signal.


Just flash, however I haven't the slightest clue on how to wire an op amp.


They're fairly simple to use if you know some circuitry. You can find the pinout pretty easily.

#6
So then I put my signal into lug 3, run lug 2 to the ground, lug 7 takes my 9 volt input, and lug 6 is where the LED's go?
Quote by R45VT
Bastards.
#7
Yes, I believe so. Also, pin 4 goes to ground (the negative of the battery). You'll probably want to wire a switch in series with the battery as well.
#11
Im not experienced very well in circuit diagrams. Am I right in thinking that you have a traditional led circuit, with the battery, switch, led, and proper value resistors? Then you just added a transistor, using the voltage from the pickup output to trigger the transistor, completing the circuit and allowing the led to light?

In my project, I am planning to use 5 leds, which all need to be diferent brightnesses, in order to light different size holes evenly. To allow myself to tune in the brightness, I was going to add a precision pot to each led, rather than a simple resistor. Otherwise, I think that your diagram matches what I want perfectly.
#12
Quote by ohaple
Im not experienced very well in circuit diagrams. Am I right in thinking that you have a traditional led circuit, with the battery, switch, led, and proper value resistors? Then you just added a transistor, using the voltage from the pickup output to trigger the transistor, completing the circuit and allowing the led to light?

In my project, I am planning to use 5 leds, which all need to be diferent brightnesses, in order to light different size holes evenly. To allow myself to tune in the brightness, I was going to add a precision pot to each led, rather than a simple resistor. Otherwise, I think that your diagram matches what I want perfectly.


You are correct about the traditional LED circuit. That is what is on the output of the open amp. But a 741 open amp can only drive out enough current for one LED. You could probably drive a series connection of 3 or 4 LEDs from it with one series resistor but then there's no guarantee all the LEDs will be of even brightness.

If you want to drive 5 LEDs and have control over each of the brightnesses like you want, then you will need a transistor circuit to drive each of the series resistor / led combos in parallel with each other. A 741 op amp can't source enough current to do this. Each with their own series resistor which you can trim to get the final brightnesses you want
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 4, 2013,
#13
is there a way to use some transistor only as a switch, for the current from the battery, not as a way to power the led?

What is this guy doing? he wires up several? is it because they are surface mount style? Is it somehow because of the board he has in there?
http://www.youtube.com/watch?v=TMiJ2kiyY2k
Last edited by ohaple at Mar 4, 2013,
#14
Quote by ohaple
is there a way to use some transistor only as a switch, for the current from the battery, not as a way to power the led?

What is this guy doing? he wires up several? is it because they are surface mount style? Is it somehow because of the board he has in there?
http://www.youtube.com/watch?v=TMiJ2kiyY2k


Yes, there is. That's what I was getting at before. You wire up all the LEDs in parallel. You can't use an op-amp to drive 5 LEDs like that. You use a transistor to act as the power supply switch from the battery to the LEDs by using the input transistor base as the trigger from the pickups to switch the transistor on and off which also does the same for the LEDs. You still need to design it though, with component values etc to get just the right effect.

The way its done on the you tube video is because of the board he has in there. It looks to be a strip LED light controller, that he's modded to accept the pickup signal as the trigger. The LEDs he has used are also for strip lighting.

It can be done this way. The controller is just a ready made version of what I described above.
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
#16
If you didn't want to fine tune the brightness of each then just have 5 LEDs in series with one current limit resistor out of the 741 op amp. Must pick LEDs which reach brightness with 10ma (or less) forward current, 1.5v max forward voltage and change the output resistor to 150 ohm or the 741 will struggle.

To do what you want, you need to connect the op amp output into a transistor and the op amp switches the transistor in time to the pickup sounds. The transistor then switches parallel LEDs on and off. You will also need to design resistor values for that entire bit also.

EDIT: or use a higher output current op amp, like an LM7321. Then you won't need the output transistor stage after the op amp. This does then look more like my diagram. Just parallel the 5 series resistor and LED combos at the op amp output. That would be OK. A 741 would just choke and die if you did that.
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 5, 2013,
#17
The reason I need to fine tune the brightness is because I am planning to use 5 leds, all in different size holes, but want to result in the same perceived brightness. Am I right in thinking that a 10ma LED wont be very bright?

For the second option, am I correct in my understanding that the op amp will be powering the leds, using the amplified voltage from the pickups (amplified using power from the battery), acting as the power source, to just control the set of series LEDs? Will the higher output op amp require a higher voltage battery?
#18
Quote by ohaple
The reason I need to fine tune the brightness is because I am planning to use 5 leds, all in different size holes, but want to result in the same perceived brightness. Am I right in thinking that a 10ma LED wont be very bright?


LED brightness is measured in mcd. It doesn't just depend on the current passing through the LED.
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
#19
Quote by Phoenix V
If you didn't want to fine tune the brightness of each then just have 5 LEDs in series with one current limit resistor out of the 741 op amp. Must pick LEDs which reach brightness with 10ma (or less) forward current, 1.5v max forward voltage and change the output resistor to 150 ohm or the 741 will struggle.

To do what you want, you need to connect the op amp output into a transistor and the op amp switches the transistor in time to the pickup sounds. The transistor then switches parallel LEDs on and off. You will also need to design resistor values for that entire bit also.

EDIT: or use a higher output current op amp, like an LM7321. Then you won't need the output transistor stage after the op amp. This does then look more like my diagram. Just parallel the 5 series resistor and LED combos at the op amp output. That would be OK. A 741 would just choke and die if you did that.

How many LED's do you figure an LM7321 can support?
What kind of transistor would do the job aswell?
Quote by R45VT
Bastards.
#20
Quote by Viban
How many LED's do you figure an LM7321 can support?
What kind of transistor would do the job aswell?


Yeah eddie. How well a LED produces light depends on its efficiency. Light efficiency LEDs can produce the same light output for smaller foward current than bog standard ones. The tradeoff is price and availablilty. Bog standards are 10's to the dollar and readily found. High efficiency LEDs are dollars for the one and you'll need to do some searching.

And Viban, a 7321 can do 4 in parallel. If you're limited to a 9v battery, you can get 5 in series, but only if you pick LEDs with less than 1.6v forward volt drop, else you need to increase battery volts, or back off to 4 LEDs in series.

If you want a second stage transistor drive out of an op amp then most NPN transistors can drive 5 LEDs easily in parallel, with change. A BC337 or 338 which is a garden variety will do and will work with a stock standard 741 driving it. Both are cheap as chips and easily available, but the tradeoff being you need to do more circuiting

If you're set on wanting to drive 5 or more leds direct from an op amp, look up data sheets for op amps with direct current output greater than 100ma.
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 5, 2013,
#21
Quote by Phoenix V
Yeah eddie. How well a LED produces light depends on its efficiency. Light efficiency LEDs can produce the same light output for smaller foward current than bog standard ones. The tradeoff is price and availablilty. Bog standards are 10's to the dollar and readily found. High efficiency LEDs are dollars for the one and you'll need to do some searching.

And Viban, a 7321 can do 4 in parallel. If you're limited to a 9v battery, you can get 5 in series, but only if you pick LEDs with less than 1.6v forward volt drop, else you need to increase battery volts, or back off to 4 LEDs in series.

If you want a second stage transistor drive out of an op amp then most NPN transistors can drive 5 LEDs easily in parallel, with change. A BC337 or 338 which is a garden variety will do and will work with a stock standard 741 driving it. Both are cheap as chips and easily available, but the tradeoff being you need to do more circuiting

If you're set on wanting to drive 5 or more leds direct from an op amp, look up data sheets for op amps with direct current output greater than 100ma.

Well what would one assume this BC337/8 can handle? also, assume I also have the option to step it up to 18 volts with 2 9 volts
.
Quote by R45VT
Bastards.
#22
Quote by Viban
Well what would one assume this BC337/8 can handle? also, assume I also have the option to step it up to 18 volts with 2 9 volts
.


A 337/338 could probably handle 10 LEDs in parallel. But your 9v battery won't last long though powering 10 LEDs.

Yeah you have tons of options. Double up on batterys, increase the LED count, use a series arrangment, use a parallel arrangement, use more powerful transistors, more powerful op amps, use bog standard LEDS, use high efficiency LEDS, even down to different LED colours have different forward voltage drops, you name it. Everything has a tradeoff of some kind.

I'm not going to go through every possible combination you guys might be thinking of doing.

Settle on one idea out of all the possible options, learn how to design it, and drive it home.
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 5, 2013,
#23
Well I'm liking 10 LED's in parallel with 2 9volt batteries, the op amp and transistor, I think I can figure out the majority of the wiring myself, however the 337 says it can put out 800mA with 45 volts. Does that sound about right? A calculator I found said that in that case I'd need a 390ohm 1W resistor, sound right?

Sorry for hounding you mate, this should be the last question
Quote by R45VT
Bastards.
#24
Quote by Viban
Well I'm liking 10 LED's in parallel with 2 9volt batteries, the op amp and transistor, I think I can figure out the majority of the wiring myself, however the 337 says it can put out 800mA with 45 volts. Does that sound about right? A calculator I found said that in that case I'd need a 390ohm 1W resistor, sound right?

Sorry for hounding you mate, this should be the last question


800ma is the max allowable. You dont actually run a BJT at the max spec collector current. Gets really frikken hot.

The circuit topology to drive a bank of LEDs would be like this

You'll need to work out the resistor values to saturate the transistor to act as a switch for the number of LEDs you want to drive at 20ma per LED.

cheers
Attachments:
Parallel LED Fanout.jpg
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
#25
Quote by Phoenix V
800ma is the max allowable. You dont actually run a BJT at the max spec collector current. Gets really frikken hot.

Hence bugera fires?
Quote by R45VT
Bastards.
#27
I dont need to drive them only with the op amp, the transistor method would work fine. I can source high efficiency LEDs with little issue. I can use 6 volts (AA pack) or 9 volts, and would like to run at least 5 leds, which can be high efficiency if it helps.

Let me try to talk through the circuit the best I can. Correct me if I am wrong (I will be using precision pots, rather than traditional resistors).

One end is the power, 9v battery. That connects to a 2 way on off switch. The switch leads to a current limiting resistor, connecting to the transistor.
The other end is from the output of the pickups, to the op amp, to the transistor.
Then, the transistor out, powered with the battery, triggered by the op amp, will go into the leds, each wired in parallel, with their own pot. Then leds and transistor to ground.

Is that mostly right? to drive 5 leds in parallel can I use the 741 op amp, and standard leds? what kind of transistor will I need?


EDIT: forgot to refresh the page before posting.... DOH. Just saw the nice diagram you posted. Sounds like I was mostly right. Thanks for your help with this. Im tech-procifient, but not a EE
Last edited by ohaple at Mar 6, 2013,
#29
Nice. what colour LEDS did you get.

Also, I think 10k base resistor will be too high.

I calc'd if using blue LEDs and a 9v supply the base resistor will be around 560ohm. The led series resistors will be about 47 ohm and the collector resistor which youve drawn as a trimpot will be around 39 ohm. If youre using different colours, the values will change slightly.
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 8, 2013,
#31
Green LEDS. let me check.

EDIT: for 5 Green leds - the series led resistors stay the same at 47 ohm each, the collector resistor changes from 39ohm to 47 ohm also and the base resistor is around 820 ohm

10k will choke the base current too much and you will get very poor LED drive

The diagram didnt have values, because the values change depending on the LED colours and thus the LED drive
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 8, 2013,
#32
I've tried my hand at this, I'm not as good at schematics and whatnot as you guys are, but how does this look in terms of function?
Quote by R45VT
Bastards.
#33
Quote by Viban
I've tried my hand at this, I'm not as good at schematics and whatnot as you guys are, but how does this look in terms of function?


While I see the intent, you cant just have wires directly into then out of the op amp

Without a resistor design to go with it, the op amp cannot discriminate between when there are no strings vibrating , which is when you want the LEDs to be dark, to when they are vibrating to which you want the LEDs to be on. It will pick up any of the tiniest electrical noise at all at its input and assume its a valid signal and will try to turn the LEDs on....all the time.

Probably better to try the op amp circuit I drew, without the series LED and resisor on the output, then see about attaching your transistor stage to that
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
#35
Quote by ohaple
So the one labeled 10k needs to be 820, and the ones by each resistor are 47?


yeah try that.

if you dont have an 820 then a 1k should still be ok
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
#36
ok, and what about the one straight off the battery/switch? I got a 1k pot. I figured that would allow for a little brightness adjustment?
Also, is the 10k pot essentially a sensitivity control?

Nevermind, didnt read you previous post carefully. You gave me all the values I need. Thanks.

As ive probably demonstrated by now, I know enough to get into trouble. Been several years since I learned to solve circuits in physics class, so I dont really remember much
Last edited by ohaple at Mar 9, 2013,
#37
Quote by ohaple
ok, and what about the one straight off the battery/switch? I got a 1k pot. I figured that would allow for a little brightness adjustment?
Also, is the 10k pot essentially a sensitivity control?

Nevermind, didnt read you previous post carefully. You gave me all the values I need. Thanks.

As ive probably demonstrated by now, I know enough to get into trouble. Been several years since I learned to solve circuits in physics class, so I dont really remember much


Well a 1k pot is way out of the ballpark. You can try it, but it need to go down to 47 ohm

yeah the 10k trim pot is a sensitivity control. Of all the values, this one is dependant on your pickup out put and all pickups are different

Also do you have a multimeter which reads V and mV? You should be testing the circuit as you go
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 9, 2013,
#38
Yeah, the pickups on mine are about average output I would say. The humbucker is pretty hot, but not as hot as my evo's. So looks like I have a couple things to change, no big deal, just a couple dollars of parts and a trip to the store. thanks for the fixes. Yes, I have a multimeter that does that. Since I have no real knowledge on how it should be reading, I have just been using it to make sure I dont make connections where I dont want them.
Last edited by ohaple at Mar 9, 2013,
#39
Quote by ohaple
Yeah, the pickups on mine are about average output I would say. The humbucker is pretty hot, but not as hot as my evo's. So looks like I have a couple things to change, no big deal, just a couple dollars of parts and a trip to the store. thanks for the fixes. Yes, I have a multimeter that does that. Since I have no real knowledge on how it should be reading, I have just been using it to make sure I dont make connections where I dont want them.


Do you have the op amp part built? dont worry about the transistor bit yet. Take out the link between the op amp output and the transistor so you can test the op amp on its own. You can test the op amp circuit by plugging the input of the op amp circuit to the guitar output jack. You can use a standard guitar cable for that. Measure the op amp output with the guitar volume controls set to off. The voltmeter should read zero, or close to. Turn up the pickup volumes. Dont hit the strings. Should still read zero. If it reads 8 or 9 volts then adjust the 10k sensitivity pot until it reads zero. Then hit the strings, should jump up to 8 or 9 volts. This is the part where the smarts are, the rest is just a dumb LED driver. makes sure the smarts work first

I've never actually built one of these before. The whole schematics and values on here I just came up with. I was going to online order the parts and just try it out because Im curious as to how well it would work first up and if it needs any tweaks.

But you beat me to it
'It takes 100 guitar players to change a light. One to change the light and 99 to stand around pointing, saying..."Yeah man, look...I can do that too"...'

My gear is in my Profile

Builds & Refurbs
Hondo 780 Deluxe
Gibson Studio
Epi LP100
Last edited by Phoenix V at Mar 9, 2013,
Page 1 of 3