Using Bicolour LEDs

mictester · Post by **mictester** » 11 Mar 2010, 18:02

I like using bicolour LEDs for effects. I use Red to show power on, but effect off, and Green for effect on. It looks good, only needs one hole in the case, and just needs one switching contact (or logic output). It's low current (and can be made lower with the use of high efficiency LEDs - just increase the upper 1k resistor value). The 10µF makes sure there's no switching noise whatsoever!

Here's the circuit:

: Bicolour LED.png (1.84 KiB) Viewed 3435 times

Give it a try - it looks really good. You can replace the upper 1k resistor with a 220 and 4V7 zener diode in series, and you'll get a battery good indicator, too!

lolbou · Post by **lolbou** » 11 Mar 2010, 19:29

These can also be used as clippers with less space, right? Never tried it though...

The red for power on and green for effect on is nice to me, but might be confusing when using non-bicolor effects?

CRBMoA · Post by **CRBMoA** » 11 Mar 2010, 19:40

I have a couple of those. I was thinking of more of a boost/fuzz pedal kinda thing. Green for 'A' and Red for 'B'. Haven't thought it through, though.

Jack Deville · Post by **Jack Deville** » 11 Mar 2010, 20:02

You can achieve three different colors by illuminating both LEDs simultaneously and varying current to each individual LED...

I.E.
1. Red LED only
2. Green LED only
3. Red and Green LED (play around with current to each LED to find a suitable level for mixing colors)

rocklander · Post by **rocklander** » 11 Mar 2010, 20:52

this is very cool mictester... I can see me using this thanks!!

do you have a similar idea for tri-colour ones? I've made the tri-vibe and 22/7 pedals which each have a 3 position switch, and thought it'd be nice to have a colour per 'mode'. on the tri-vibe I ended up using the dpdt to illuminate various colours, but couldn't figure a way to split effectively the 3 ways (obviously), but incorporating this system may have let me

mictester · Post by **mictester** » 12 Mar 2010, 05:39

Jack Deville wrote:You can achieve three different colors by illuminating both LEDs simultaneously and varying current to each individual LED...

I.E.
1. Red LED only
2. Green LED only
3. Red and Green LED (play around with current to each LED to find a suitable level for mixing colors)

You can do that, but the real point of the circuit above was that you can change over the colours with just one wire! It's just a nice way of using a spare switch way to do the two-colour thing. It looks pretty!

Also, the positive feed to the green LED can come from logic switching if that's what you're using.

Also, if you only have a "break when on" contact available, swap the LED colours and you'll still get the right result!

Jack Deville · Post by **Jack Deville** » 12 Mar 2010, 06:03

You have a background in electronic design?

cpm · Post by **cpm** » 12 Mar 2010, 10:41

i've used them on some applications:

- some kind of two channel pedals:
green: cleaner setting
green+red = ~orange: dirtier setting, only needs to activate the red LED, for example, with the same switch that engages some additional gain stage

- modulation effect, each color for effect on/off, buth both ways is showing the LFO rate on the LED blinking.

mictester · Post by **mictester** » 12 Mar 2010, 16:21

Jack Deville wrote:You have a background in electronic design?

Yes. It's how I make some of my living. I've designed for some major manufacturers over the last 30 years.

Dr Tony Balls · Post by **Dr Tony Balls** » 12 Mar 2010, 20:13

Not to take away from what is obviously a constructive, informative post, but why the need for the extra circuitry?

Assuming you're using a 3PDT for your stomp switch, why not just wire the common anode to your 9V supply, and then each cathode to an end on your switch? with a current-limiting resistor in there wherever you please, but something like this:

Jack Deville · Post by **Jack Deville** » 12 Mar 2010, 23:02

The extra circuitry allows one control wire, instead of two!

mictester · Post by **mictester** » 12 Mar 2010, 23:09

Dr Tony Balls wrote:Not to take away from what is obviously a constructive, informative post, but why the need for the extra circuitry?

Assuming you're using a 3PDT for your stomp switch, why not just wire the common anode to your 9V supply, and then each cathode to an end on your switch? with a current-limiting resistor in there wherever you please, but something like this:

Often I don't have a whole way available on the switch - using the extra resistors allows a single wire to switch the two LEDs. That's the whole point! I often use logic to switch my effects (CMOS switches are quieter than ANY mechanical switch), and often, I just have a line that goes "high" for effect on (or "low" in a couple of instances - swap the LED colours, and you can use "active low" into the red LED for the same result).

Using the resistors in that way, and with the differential in the voltage drop across LEDs of differing colours, you can use just the one wire for switching... oh never mind. Go back to your fragile, expensive, unreliable, unnecessary 3 pole foot switches!

Jack Deville · Post by **Jack Deville** » 12 Mar 2010, 23:11

HA!
those damned switches are GARBAGE!!

mictester · Post by **mictester** » 12 Mar 2010, 23:22

cpm wrote:i've used them on some applications:

- some kind of two channel pedals:
green: cleaner setting
green+red = ~orange: dirtier setting, only needs to activate the red LED, for example, with the same switch that engages some additional gain stage

- modulation effect, each color for effect on/off, buth both ways is showing the LFO rate on the LED blinking.

Yes. I've just built a couple of pedals with Big Muff Pi (sort of) on one side, and Tonebender on the other. There are two footswitches - one for "Effect /Bypass" and one for "Mode". The BMP controls have red tops, and when that effect is selected, a 10mm bicolour LED lights up bright red, and the Tonebender controls have green tops, and when selected, the LED shows bright Green. It looked really good to me, and the guy who wanted the boxes thought that it was amazing (guitarists love flashing lights!).

I've also just built a couple of pan boxes. I used bicolour LEDs to show routing (the box is a stereo panner, and you can stop the pan at any point). In this instance, I was a bit more subtle, and used PWM to change the colour of the LED from red on the right output to green on the left, with yellow in the middle. It looked fabulous!

One word of advice - find the LEDs that give you the most light output for the least current - particularly if you're using battery supplies. There's no point in building your effect to draw just 2 or 3 mA and then take 30 mA for the indication! I find that the "Kingbright" high efficiency LEDs are the best compromise of luminous intensity against current drawn, though of course you may have your own favourite - let us all know what you've found and where they're available!

soggybag · Post by **soggybag** » 13 Mar 2010, 07:54

Very cool Idea. I'll have to give this a try. Suggest a part number. I have a few bi-color LEDs that come in different arrangements. Some are three leads. The others are two leads.

mutetourettes · Post by **mutetourettes** » 29 May 2011, 21:14

Hi there - well isn't what's being described here a tricolour LED? ie three legs and can do red, green, or red+green=yellow ?
I went and bought a bi-colour LED and it's only got two legs with the different colours backwards and forwards (ie it's two diodes in parallel opposite arrangement) those are a royal pain in the ass to arrange a simple circuit for.....

Barcode · Post by **Barcode** » 02 Jun 2011, 21:24

mutetourettes wrote:Hi there - well isn't what's being described here a tricolour LED? ie three legs and can do red, green, or red+green=yellow ?
I went and bought a bi-colour LED and it's only got two legs with the different colours backwards and forwards (ie it's two diodes in parallel opposite arrangement) those are a royal pain in the ass to arrange a simple circuit for.....

There are two types of bicolor LED's. There are 3 leg bicolor LEDs that actually contain two elements, one for each color.

Then there is the kind you got most likely, which has two legs like a normal LED but the color can be changed with varying the level of current going to the LED. It has internal circuitry that changes the color based on current.

In your case, you couldn't utilize the above circuit, but the same one-wire control could be achieved by utilizing parallel resistors.

rocklander · Post by **rocklander** » 02 Jun 2011, 21:34

I've seen the type he means (and have some). they're polarity controlled.
hook up volts across it one way and get one colour, reverse the polarity and get a different one.