Problem with RGB LED color combinations.

Thread Starter

lilrips1

Joined May 7, 2010
44
jason 77: Yes, Thanks. Since I am using a breadboard to test the LED, I described it in terms of breadboard rows. Each row has multiple holes that are connected.

Audioguru: Nope, each anode lead has its own breadboard row, so they are not connected.
And yes, when I connected only the green to the power supply, green light went on.
-only the blue to the power, blue light went on
-only the red lead to the power, the red went on
-blue and green to the power, both turned on
-blue and red to the power, only red turned on
-green and red to the power, only red turned on

SgtWookie: For the red I tried 150 ohms and 100 ohms, but an online LED resistor calculator specified 100 ohms. Although, for the ~100 ohms, I added two 47 ohm resistors in series (I figured it out). Six ohms wouldn't make too much of a difference would it?

And yes, that PEBBLE drawing is pretty much what my setup looked like, except I didn't connect the resistors directly to the power bar. I had the LEDs one more section over (A-E in your picture, not shown), one end of the resistors in the first section (J-F) and one end in the LED section, with jumpers going from the power to the first section.

If necessary I could get a picture tonight when I get back home to experiment some more.
 

Adjuster

Joined Dec 26, 2010
2,148
Is there any chance that your nominally 4.5V supply is dropping when you connect the LEDs?

What are you using for the supply - if it is a battery, could this be getting exhausted?
 

CDRIVE

Joined Jul 1, 2008
2,219
Do you have a Harbor Freight outlet near you? You can buy a DMM dirt cheap from them.

Meter-less Power Supply Voltage drop Test:

Use a single LED (any color will do but blue would be best) and appropriate limiting resistor. Then connect it across your power supply lines on the Proto Board but with the V+ disconnected from your RGB array. When connecting power to the RGB array, observe the Pilot LED to see if it dims substantially while you're testing each LED combination.
 

SgtWookie

Joined Jul 17, 2007
22,230
A picture is worth a thousand words.

It is very difficult to take a clear, well-focused photo indoors using artificial lighting; the result is usually pretty poor. A cameras' flash doesn't work well at all unless you can bounce the light off a wall or something; otherwise the lighting is very harsh and much too high in contrast.
 

Thread Starter

lilrips1

Joined May 7, 2010
44
However, this LED is being controlled by three JK flip flop gates Q outputs, and the TTL chips take 5V, and I think they output 2.4/3.4 volts min/max. So, what I am concerned about then, is when I have a dual JK IC outputting Q1 high and Q2 high, will each be 2.5 V since it is a 5V power supply? If so, then I will definitely need transistors, because the 5v power suplly is required for the ICs and I cannot use 9v, correct?
 

thatoneguy

Joined Feb 19, 2009
6,359
Get a meter, this thread would have never existed if you had one. Not that we don't enjoy new members, by any means. However, we can help you a LOT easier if you have some basic and cheap equipment. A DMM can be bought for the price of your RGB LED!
 

SgtWookie

Joined Jul 17, 2007
22,230
However, this LED is being controlled by three JK flip flop gates Q outputs, and the TTL chips take 5V, and I think they output 2.4/3.4 volts min/max. So, what I am concerned about then, is when I have a dual JK IC outputting Q1 high and Q2 high, will each be 2.5 V since it is a 5V power supply? If so, then I will definitely need transistors, because the 5v power suplly is required for the ICs and I cannot use 9v, correct?
Now you're providing a lot more relevant/valid information.

If you're working with the really "old school" LS TTL, a logic "1" is more like 3.8v at low current, and a logic "0" is just under 0.8v.

You need to specify the complete part number of the IC that you're using to source/sink current to/from the LED.

TTL is generally not capable of sourcing much current. 74HC might source up to 20mA current under certain circumstances.
 

Audioguru

Joined Dec 20, 2007
11,248
However, this LED is being controlled by three JK flip flop gates Q outputs, and the TTL chips take 5V, and I think they output 2.4/3.4 volts min/max. So, what I am concerned about then, is when I have a dual JK IC outputting Q1 high and Q2 high, will each be 2.5 V since it is a 5V power supply? If so, then I will definitely need transistors, because the 5v power suplly is required for the ICs and I cannot use 9v, correct?
Why didn't you tell us in the beginning that you are using +40 years ago old TTL parts??
Oh. Maybe this is a school assignment. Teachers like old parts.
 

Thread Starter

lilrips1

Joined May 7, 2010
44
Whoah, I was not testing the LED with the ICs this entire time. I hope that's not what you guys are thinking. I haven't done that yet. I was just using the LED and resistors, only trying to get the LED setup correctly.

The reason I am using TTL is just because that's what I am used to using.
Here is the datasheet.

It says the high level output current is -.4 mA ...

I did pick up a meter at RadioShack, since that's the only store near me that sells them. It was $20 plus $7 for the 12V battery. :cool:

I appreciate the help!
 

Thread Starter

lilrips1

Joined May 7, 2010
44
Well I suppose my teacher is who introduced them to me, but I'm using them now for this project. He used them for educational lab purposes I assume.

Should I be using CMOS?
 

SgtWookie

Joined Jul 17, 2007
22,230
Whoah, I was not testing the LED with the ICs this entire time. I hope that's not what you guys are thinking. I haven't done that yet. I was just using the LED and resistors, only trying to get the LED setup correctly.

The reason I am using TTL is just because that's what I am used to using.
Here is the datasheet.

It says the high level output current is -.4 mA ...

I did pick up a meter at RadioShack, since that's the only store near me that sells them. It was $20 plus $7 for the 12V battery. :cool:

I appreciate the help!
Look, TTL sourcing current sucks.

That's why you're having problems.

You were trying to drive multiple LEDs from a source that wasn't capable to do so.

End of story.
 

Thread Starter

lilrips1

Joined May 7, 2010
44
Well, no, I wasn't driving the LEDs from the TTL chips. As I just said (9:42 PM), I was only using the LED and resistors, with the battery as the direct source.

What I posted at 8:08 pm was a question asking how the LED would work with the flip flops. I probably should have said "...this LED needs to be controlled by three JK..." Sorry.
 

SgtWookie

Joined Jul 17, 2007
22,230
You can use the flip-flop outputs that go low to turn on an LED in series with a resistor.
That's true, if you have individual LEDs, or a common anode RGB LED (or various other types of multicolor LEDs) - unfortunately, our OP's RGB LED is common cathode; so they have to source current to the separate anodes.
 

SgtWookie

Joined Jul 17, 2007
22,230
The only thing I can think of now is that the power source is getting pulled down by the load of the LEDs; ie: tired batteries or a weak power supply. It'll take measuring with a multimeter/DMM to find out if that's what is occurring.
 
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