RGB LED as Status Indicator

Frequent question abouts LED and other types of diodes.
Post Reply
User avatar
cacophony
Breadboard Brother
Information
Posts: 57
Joined: 20 Jan 2009, 06:36

Post by cacophony »

Here's the plan:
2 independent channels in a single box (an overdrive and a booster) with 1 slot for 5mm RGB (common anode) LED for status indicator.

So I came up with a switching circuit that performs the following:
1) If the booster is on while the OD is bypassed, red color will light up.
2) If the OD is on while the booster is bypassed, green color will light up. &
3) If both are on, blue color will light up.

The thing is, I tried to test this circuit on a breadboard but only green and red colors are working fine. But when I test the blue part out of the circuit with a simple battery and resistor, it is still working.

Questions are:
1) Could I have missed something in the circuit? I assume logic diagram is 99.9% correct.
2) Could I power the inverter and AND gates more than +5VDC?

Thanks in advance.

Nicko
Attachments
lights.png

User avatar
mictester
Old Solderhand
Information
Posts: 2923
Joined: 11 Sep 2008, 20:29
my favorite amplifier: Mesa Boogie, Roost Sessionmaster, AC30
Completed builds: Hundreds! Mostly originals, a few clones and lots of modifications.
Location: Somewhat closer to Amsterdam than before!
Has thanked: 32 times
Been thanked: 844 times
Contact:

Post by mictester »

Your logic looks OK. however, you can't power the 74LS ICs with more than 5 Volts or they will get very hot and die! What series resistor values are you using for current limiting / dropping to the LED elements? You may not have enough current available for the blue part of the LED.

I prefer to use CMOS - it's much less current hungry, and works OK on any voltage from 3V to 18V, though for the kind of circuit you're proposing, I'd use four transistors, some diodes and some resistors!
"Why is it humming?" "Because it doesn't know the words!"

User avatar
KMG
Solder Soldier
Information
Posts: 209
Joined: 02 Feb 2010, 20:26
Location: Russia
Has thanked: 5 times
Been thanked: 80 times
Contact:

Post by KMG »

In my opinion it is simpler generally without the logic
Leds.jpg
Leds.jpg (9.67 KiB) Viewed 2337 times
Image

User avatar
mictester
Old Solderhand
Information
Posts: 2923
Joined: 11 Sep 2008, 20:29
my favorite amplifier: Mesa Boogie, Roost Sessionmaster, AC30
Completed builds: Hundreds! Mostly originals, a few clones and lots of modifications.
Location: Somewhat closer to Amsterdam than before!
Has thanked: 32 times
Been thanked: 844 times
Contact:

Post by mictester »

KMG wrote:In my opinion it is simpler generally without the logic
Leds.jpg
You're right except that you'd need current limiting / dropper resistors for each section of the LED. The reason that I'd use logic is that I'd use momentary switches and CMOS analogue switches (4066 or 4053) and could do all sorts of clever switching schemes with little effort.
"Why is it humming?" "Because it doesn't know the words!"

User avatar
lolbou
Old Solderhand
Information
Posts: 2617
Joined: 18 Nov 2008, 21:38
Has thanked: 308 times
Been thanked: 225 times

Post by lolbou »

mictester wrote:You're right except that you'd need current limiting / dropper resistors for each section of the LED.
Even if one part of the LED is used at one time?
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
mictester
Old Solderhand
Information
Posts: 2923
Joined: 11 Sep 2008, 20:29
my favorite amplifier: Mesa Boogie, Roost Sessionmaster, AC30
Completed builds: Hundreds! Mostly originals, a few clones and lots of modifications.
Location: Somewhat closer to Amsterdam than before!
Has thanked: 32 times
Been thanked: 844 times
Contact:

Post by mictester »

lolbou wrote:
mictester wrote:You're right except that you'd need current limiting / dropper resistors for each section of the LED.
Even if one part of the LED is used at one time?
Yes - the red part will need the least current, the green a bit more and the blue most of all. The voltage drop across the segments will vary too.

Incidentally, I used to use a bi-directional Red / Green LED (actually two LEDs in the same package wired in opposite directions) for asymmetrical clipping in my pseudo-Tubescreamer pedals, because of the difference in the voltage at which the sections went into conduction.
"Why is it humming?" "Because it doesn't know the words!"

User avatar
lolbou
Old Solderhand
Information
Posts: 2617
Joined: 18 Nov 2008, 21:38
Has thanked: 308 times
Been thanked: 225 times

Post by lolbou »

mictester wrote:Yes - the red part will need the least current, the green a bit more and the blue most of all. The voltage drop across the segments will vary too.
Oh ok... I would have expected the different colors requirements to be matched since these are in the same package. I've never used bicolor LEDs for anything, but as I suggested in your thread, I've thought once about using them for clippers.

Obviously I would have expect a symmetrical clipping :slap: ...
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

User avatar
KMG
Solder Soldier
Information
Posts: 209
Joined: 02 Feb 2010, 20:26
Location: Russia
Has thanked: 5 times
Been thanked: 80 times
Contact:

Post by KMG »

mictester wrote:You're right except that you'd need current limiting / dropper resistors for each section of the LED. The reason that I'd use logic is that I'd use momentary switches and CMOS analogue switches (4066 or 4053) and could do all sorts of clever switching schemes with little effort.
What can you say about this schematic
Leds.jpg
Leds.jpg (15.18 KiB) Viewed 2314 times
But if you use non latching momentary switches you need to use triggers to hold state after switch is released.
Image

User avatar
KMG
Solder Soldier
Information
Posts: 209
Joined: 02 Feb 2010, 20:26
Location: Russia
Has thanked: 5 times
Been thanked: 80 times
Contact:

Post by KMG »

For non latching switches i use TinyAVR.
It allows to implement any comlex switching algorothm.
Example of schematic i use in preamps. It can be powered by 5 or 9/12V and use 5 or 9/12V relays or pass ccontrol to analog cmos switches depending on assembly.
Image
Image

User avatar
cacophony
Breadboard Brother
Information
Posts: 57
Joined: 20 Jan 2009, 06:36

Post by cacophony »

KMG wrote:In my opinion it is simpler generally without the logic
Leds.jpg
Case solved. I never thought of this simpler wiring. Thanks a lot! :applause:

User avatar
cacophony
Breadboard Brother
Information
Posts: 57
Joined: 20 Jan 2009, 06:36

Post by cacophony »

I forgot to mention. If both channels are bypassed, no color will light up. I guess I really have to go with logic gates. What do you think guys?

User avatar
KMG
Solder Soldier
Information
Posts: 209
Joined: 02 Feb 2010, 20:26
Location: Russia
Has thanked: 5 times
Been thanked: 80 times
Contact:

Post by KMG »

You can use 4052 to implement drive leds logic.
Leds.jpg
Also you need to use transistors to drive leds because cmos logic/switches can draw only 1-2 mA through them.
Image

Post Reply