Common Cathode RGB LEDs with LEDWiz?

[arzoo]

Six months ago I purchased a bunch of RGB LEDs from an ebay auction. At the time, I'm pretty sure I specified common anode. Today I finally had time to try them out and I think they are common cathode. Since the LEDWiz uses a common +5v with the return at each port, I don't think I can use a common cathode RGB. 

[protokatie]

Six months ago I purchased a bunch of RGB LEDs from an ebay auction. At the time, I'm pretty sure I specified common anode. Today I finally had time to try them out and I think they are common cathode. Since the LEDWiz uses a common +5v with the return at each port, I don't think I can use a common cathode RGB. 

I was going to suggest using a Not Gate on the LEDs, but that wouldnt work. Then I thought about you using a transistor or relay that is triggered by the LEDwiz to control a seperate powersupply to each LED element. That would work, but would most likely cost more than just buying the proper RGB LEDs... Other than that, I have no quick or easy solution in mind...

[MonMotha]

You can use a PNP or PMOS transistor to drive the LEDs on the high side.

For a PNP, put a resistor in line with the base and use the LED Wiz output to drive that.  2.2k should be about right.  Emitter goes to +5; collector goes to the anode of the LED.  Common cathode on the LED goes to ground.

For a P MOSFET, use a "pull-up" resistor to +5 of about 10-100k on the gate.  Then have the LED Wiz drive the gate (it will ground out that pull-up to create the gate signal).  Source goes to +5; drain goes to the LED anode.  LED common cathode again goes to ground.

A collection of PNP transistors can still be had at some Radio Shacks for like $2 for 10-15.  A good option if you have to buy them by part number is the 2N3906.

[Franco B]

Or you could just buy some common annodes 

How many do you need? I have a fair few, I could send you some over if you need 20 or so, it would be the least I could do with what you have done with LED Blinky etc.

[protokatie]

MonMotha and franco are both just saying what I said. (although MonMotha is being a bit more specific). IMHO, Just buy new RGB LEDs (unless you bought like 100 of them....)

[arzoo]

Guys,
Thanks for all the help - and Franco, thanks for the offer, I may take you up on it. I had purchased 50, but I was only going to wire up 16. I sent the seller an email to see if they would swap for the common anode versions. Let's see what they do.