LED question

[frogman]

Ive recently finished soldering up a box of hall reverb on vero board.

http://3.bp.blogspot.com/-S1mac2DalyY/T6OsSIVA9uI/AAAAAAAABa8/jArJBxnw6Fs/s1600/Box+of+Hall+-+culturejam+-+BTDR-2H_B.png

I am wiring the 3pdt footswitch like this.

http://www.seymourduncan.com/forum/attachment.php?attachmentid=53741&stc=1&thumb=1&d=1399090434

My question is: Will I be able to solder the positive end of the LED to the dc jack on the same prong that the 9v (top left of vero layout) connects to? How about the other positive terminal of the dc jack? I have also heard of a resistor being necessary on the positive side?

[anotherjim]

That sound right, and yes, you do need a resistor in series with the LED (about 680ohm on 9volts).

Personally, I think it's best practice to minimize the number of wires in the box that directly carry the full power supply voltage. It reduces the risk of short circuits when you're messing around trying to find a fault.
So, I put the resistor, connected to existing positive supply, on the circuit board -  the led and switch are wired between the resistor and negative.

[Quackzed]

yep you need a resistor in series with the led, without it the led will burn out from too much current 1.2k is common, either side of the led + or - is ok as long as its in series with the led...
the 2 positive dc jack leads are for 'switched' power, the connect together when no wallwart plug is inserted and disconnect when one IS.
this is to disconnect the positive battery lead from the circuit when using wallwart power, so the 'switched' lead of the dc connector only goes to the + battery lead and the other goes to the board +9v spot, led+ can go tto that lead of the dc jack or to the board +9v spot, they're both the same 'connected' thing...

[deadastronaut]

+1 on the comments, the resistor value will also depend on the led used too....and your preference for bright lights/retina destruction  etc..

1k-4.7k for red/green/yellow diffused standard leds...is ok

but for superbright clears ive gone up as far as 10k-15k to reduce glare...they can get pretty bright/harsh..

[GoranP]

i dont care for scorchers and regularly go above 30k for chinese waterclear superbrights. i even have a little makeshift test rig to check for brightness before i put the led in the box.

[deadastronaut]

^ yeah, very wise, i always test with a resistor sub box..then decide.

[frogman]

I am using an extra bright one. I have some 4.7 and 6.8k's that ill probably use. What I am getting from this is, the higher value the resistor, the dimmer the LED, correct?

I also have a question about pulldown resistors. I usually see one with a value of 2.2M between input and ground. I barely see them between output and ground, but can there be one there too to reduce popping?

[Quackzed]

yep, higher resistor = lower current through the led = dimmer led
high value resistor at the input to avoid pops, but most fx have a volume pot at the end ,so you don't need to add  a big pop resistor at the end, its already there(volume pot)... in your schem theres a 33k to ground right before the output so you don't need to add anything, if you added a 2m2 to that point, it'd be in parallel with that 33k and it wouldn't add any advantage, the 33k would overwhelm the 2m2 by being a much lower value/ an easier path to ground. also fx pedals have transistors or op amps that can drive a load (resistance to ground) much better than a passive guitar can and so dont need big resistors like 2m2. basically a passive guitar pickup will lose treble without a big input impedence (high resistance value) where an active transistor or op amp or other amplifying device will have no problem driving resistances that are much lower, like that 33k. so large value resistors are used at the input of a circuit, but aren't needed at the end of the circuit due to the 'driving' abilities of the circuit.

[frogman]

Another question.

Could i have resistors on each terminal of an led (one between cathode and footwswitch, one between anode and power supply)? Would the resistance then be the sum of both resistors?

[PRR]

> Could i have resistors on each terminal of an led (one between cathode and footwswitch, one between anode and power supply)?

You can use as many resistors as you want. I once had 13 resistors doing "one" job. (I needed one big resistor, a box of medium resistors literally fell off a truck, I was poor.)

> Would the resistance then be the sum of both resistors?

Yes.

The drawback is that you paid twice as much as you "had to".

There can be advantages, when you don't have the right value handy, or you need two wires which might as well be resistors. Personally I would prefer "add-up to get a good value" resistors to be together, so I know what happened; and resistors are rarely good jumper wires. But the electrons don't really care.

[karbomusic]

but for superbright clears ive gone up as far as 10k-15k to reduce glare...they can get pretty bright/harsh..

^This... I usually only use super bright clears which are basically little retina destroyers.   I've used upwards of 22k to calm those fellas down but the current savings is outstanding. I also tend to soften them up with 4x steel wool.

[frogman]

> Could i have resistors on each terminal of an led (one between cathode and footwswitch, one between anode and power supply)?

You can use as many resistors as you want. I once had 13 resistors doing "one" job. (I needed one big resistor, a box of medium resistors literally fell off a truck, I was poor.)

> Would the resistance then be the sum of both resistors?

Yes.

The drawback is that you paid twice as much as you "had to".

There can be advantages, when you don't have the right value handy, or you need two wires which might as well be resistors. Personally I would prefer "add-up to get a good value" resistors to be together, so I know what happened; and resistors are rarely good jumper wires. But the electrons don't really care.

I realize that resistors in series = the sum of resistors. I meant to emphasize the part about simultaneously having a resistor coming from both the cathode (to fottswitch) and anode (to power supply). Will it have the same effect as two resistors series on just one side of the led?

[Tony Forestiere]

Yep. Those resistors will only pass the current they can dissipate throughout that circuit segment, and the LED will only consume the current the resistors allow.

(Did I get it right?)

[antonis]

Just a question here..
(for not creating another thread..)

I found some days ago a batch of Green LEDs (5mm) in my junkbox and trynig to test them I used - by mistake - a 15k resistor (instead of a 1k5) at 9VDC..

The LEDs glowed enough (to use them as a status indicator on a pedal) even with a 22k resistor..!!!

Can this be true or my eyes (and my mutimeter) need replacement..??

[bluebunny]

Can this be true

Yep!

[bluebunny]

Furthermore, a larger resistor can avoid this scorching result.          <--- Warning!!     

[antonis]

Can this be true

Yep!

Thanx man..!!!
(you saved me a lot of money for an ophthalmologist..)

I didn't know that I've got "ordinary" looking LEDs with working current of 3μA...

[frogman]

Yep. Those resistors will only pass the current they can dissipate throughout that circuit segment, and the LED will only consume the current the resistors allow.

(Did I get it right?)

I think. I ended up just doing it and wiring a resistor on each terminal of the led like i described and it dimmed the led just enough.

[PRR]

> Green LEDs... I used - by mistake - a 15k resistor (instead of a 1k5) at 9VDC.. working current of 3uA...

9V minus about 2V for green LED is 7V across the resistor.

7V across 14K is a half a milli-Amp (466uA), not three micro-Amps.

Outdoor sky light is about 5,000 foot-candles, evening living-room light is about 5 foot-candles, a 1,000X change; so it is no big shock that a 40X change of LED power (20mA max, 0.5mA on the bench) is fine to the eye.

If you do a lot of summer noon gigs, you may want that 20mA. But many of us play after dark in dim-lit rooms, and half-mA is often plenty bright.

[antonis]

My bad (again..) Paul..

I intented to write down 300μA (not 3μA.. ) because this current value was calculated (and measured) with a 22k resistor..

I was surprised because the specific batch of LEDs is an "ordinary" one (5mm, no low current)..
I used to use them as indicators on custom made power supplies, battery chargers e.t.c with working current more than 5mA to get a reasonable light emission in room environment..