I am totally new to electronics. Trying to do a quick crash course to do a project with my son, while he is here for 10 days visiting.
I seem to be on the right track from my reading. Plan to control LED RGBs (common anode) with TLC5940's. Seems 5940s work only with common anode rgbs from what I read.
Ok, so Anode is the positive side of the LED (the small part). So instructions tell me to put a 5v current to the common anode, then resistors on the negative side? When I learned to use resistors for one color LEDs, all instructions told me to calculate the resitor value I needed, then put it on the positive side (anode). Will the same value resistor do the same job if placed on the negative end (cathode)?
I did try to do a search, but I don't think I have enough key words, as all I seem to get is websites selling me RGB leds, or insturctions telling me to put resitors on the cathode end, which contradicts what I've read before that resistors go on the positive side.
For a simple led circuit, no matter where the limiting resistor is, it only has to be in series with led. But inside a complex circuit, voltages will change, and things may not work if changing position of led and resistor.
Ok, I think I understand a bit better. I am planning to multimplex two daisy chained TLC5940s to control 30 RGB LEDs with common anode with an arduino.
These are the specs of the RGBs
RED: Typical: 2 V Max: 2.4V
GREEN: Typical: 3.4 V Max: 3.8V
BLUE: Typical: 3.4 V Max: 3.8V
So I can control the max voltage of the 5940's with one resistor. I would do the math, then set it to 3.4 volts or lower. Would I then simlply do the math of what resistor would be needed to drop from 3.4 to 2.0, and then add one resistor to each negative (cathode) for the red LED portion?
30 RGB LEDs is considered simple not complex correct?
So I can control the max voltage of the 5940's with one resistor.
No.
The TLC5940 does not control voltage at all.
It is a current sink you control it for all the channels using one resistor.
So instructions tell me to put a 5v current to the common anode
No they did not. They told you to connect a 5V voltage to the common anode. And they did not say common because that is wrong if you want to use a common anode RGB LED it has to be in the cathode.
So I can control the max voltage of the 5940's with one resistor.
No.
The TLC5940 does not control voltage at all.
It is a current sink you control it for all the channels using one resistor.
So instructions tell me to put a 5v current to the common anode
No they did not. They told you to connect a 5V voltage to the common anode. And they did not say common because that is wrong if you want to use a common anode RGB LED it has to be in the cathode.
Mike thanks for taking the time to reply. I do not hide the fact that I am a total newbie and I do make it obvious by my questions. I do understand that voltage and current are different, but I often make the mistake of using the words interchangeably.
If I understand correctly, the "anode" is the positive side of an LED, and the cathode would be the negative end. I am under the impression that I would connect a 5v voltage (positive) to the common anode (of the RGB LEDs), and the TLC5940 would be completing the circuit turning the LED on and off.
Not sure what you meanb by "if I want to use a common anode RGB LED it has to be in the cathode". I would run a 5v current through the cathode? Doesn't the cathode connect to ground?
I do understand that voltage and current are different, but I often make the mistake of using the words interchangeably.
That is fine, but they are very different things and expect to be corrected until you get it right.
If I understand correctly, the "anode" is the positive side of an LED, and the cathode would be the negative end
Yes.
Not sure what you meanb by "if I want to use a common anode RGB LED it has to be in the cathode"
I was referring to the current limiting resistor when I said "it". Normally it does not matter but with a common anything RGB LED the resistor has to be in the leg that is not the common one.
I am under the impression that I would connect a 5v voltage (positive) to the common anode (of the RGB LEDs), and the TLC5940 would be completing the circuit turning the LED on and off.
Yes that is right. With that chip you do not need a resistor in the LEDs at all because the chip acts as a current limiter for each individual LED.