With a common anode LED, you connect the LED to the positive power supply (5V) and to an I/O pin, via a resistor. Setting the pin LOW makes the LED light up. With a common cathde LED, you connect the LED to the negative power supply (Gnd) and to an I/O pin, via a resistor. Setting the pin HIGH makes the LED light up. With darlington driver chips like the ULN2803, you can't set the pin HIGH, so they only work with common-anode LEDs. Anode = positive end of LED, cathode = negative end of LED.
Pull-up and pull-down resistors are only used with input pins.
I wouldn't recommend connecting the three LED cathodes in parallel as you have shown. The three LEDs will have different forward voltages, and so the one with the lowest forward voltage will light up and the one with the highest will be dim. Best to have one resistor per LED. Yes, I know it's a lot of resistors, but that's how these circuits turn out!
Pin 9 to +5V is correct. As Mike says, connect the common anodes of the RGB LEDs to +5V. PWM will work via a ULN2003.
ok then, ill put up another Schematic when i finish it, this forum needs some sort of reputation system you guys would of already would of gotten more that Half a dozen reps from me.
Now you've made the schematic worse! You have swapped the LEDs around to common-cathode types. You need the common-anode types, and connect the left-hand end (as shown on the diagram) to +5V, not Ground.
Those LEDs, by the way, come with resistors for 12V, but you need resistors for 5V.
yeah and remember when you are buying the resistors, you need 3 times as many resistors as LEDS. Also I'd buy different resistors for all the color cahnnels dependong on the volage drop.
1.should i just draw the power from the USB, or should i use the +5v that i have been using?
2. if i use the +5v pin will it disconect the USBs power automaticly?
I'm thinking of making something similar ( have some RGB-led strips, common anode) but they run on 12v. Do I understand this uln2003 correctly when I can just connect an external 12volt power supply on pin 8+9 and the pwm outputs to input 2-7 or do I say something stupid now.
Deodupke, if you are using a Arudino you have to use 5v for pin 9 i believe. as that is the same voltage that the Arduino outputs
pin 9 goes to ground
what sort of LEDs are you using could you just change your resistors to something more suitable for 5 volts.
im going to get this designed made properly on a PCB, your are welcome to one of the 4 extra PCBs i will have afterwards
here is the service i will be using http://www.seeedstudio.com/depot/propaganda-pcb-service-p-316.html
the cost would be $5 for the PCB and $5 shipping directly to you
because i cant guarantee that the design will work i am happy to refund if there is design problem. there shouldn't be one :p.
haha
