16 RGB LED's in parallel controlled by atmega328 PWM pins for pc case mod. (Updated)

Question

Ok I'll start by saying i'm totally new to electronics, (Java programming is my hobby) I'm also new to this site, (The Ben Heck Show brought me here). Basically I have a really cool plan for a PC build I just completed, all of the fans have 4 blue LED's. I want to replace those with RGB LED's Allowing me to choose any colour I like to suit my mood. The controls will be mounted in an empty 5.25" drive bay, And consist of 4 push buttons and an RGB led. Button 1: Mode (Cycle through pre-set colour cycling modes, and static user defined color) Button 2: + Button 3: - Button 4: Colour Select (R, G, B) You cycle through the pre-sets with the Mode button pre-set X > pre-set X > user defined The front panel RGB LED will be off while in pre-set mode, when you reach user-defined mode the led will light fully red indicating that the + and - buttons will affect the Red value of the fan lights Pressing the Color Select button will cause the front rgb led to change to Blue allowing you to alter the Blue value, a further press changes to green then back to red I'm also hoping in the future to have control over serial from a program running on the pc I intend to write (using one of those SparkFun USB to serial breakout boards connected to an internal USB header) https://www.sparkfun.com/products/718 The entire lighting system will get its power from a 4 pin molex connector coming from the PC PSU I mocked up a schematic of the circuit in Fritzing, I'm guessing it will work properly, however I may be totally incorrect and pop something The Micro-controller used will be an ATMEGA328 with the arduino boot loader mounted in a socket on the PCB its supply voltage will come from the 12V pin of the Molex through a 7805 Voltage regulator Was also wondering could I do-away with the voltage regulator and power the chip directly using the 5V pin of the molex? Fullscreen 5415.contentimage_76492.html Download Jive SBS Error
An general error occurred while processing your request. The connector labelled C4 will go to the LED's The RGB LED's will be Common Anode each colour connected in parallel each with its own current limiting resistor , they will be switched using 3 NPN Transistors one for each colour. From my calculations based on figures I found on-line each LED colour drawing 20ma * 16 = 320ma per colour channel so my transistors need to be able to switch that load My main question, Will this work how I have designed it, or will I destroy something? and is there a better way? Edit: After doing some research i found using common cathode RGB LED's with PNP transistors wouldn't have worked the way I intended, so i have updated the schematic to reflect this

mcb1 · Accepted Answer

Oops I posted and you updated while I was constructing the reply. Normally a drawing doesn't match the physical layout, however this is a good exercise to get you thinking about avoiding the pitfalls. As you become more familiar with electronics these become second nature ... but they still creep up behind you and slap you if you are sloppy. If you build it very similar to your drawing (ie laying it out in the same manner), you should avoid any potential headaches. one minor edit ... I'd make the 10k on the reset connect to the ATmega supply line, rather than the 5v to the leds. Well done. Now the code .... Cheers mark

mcb1 · Answer

The only comments I 'd make is that AREF isn't tied to 5v on most other boards. It can be set under software so they usually keep it isolated. You also seem to have no high freq filter caps (0.1uF) showing across the supply lines R54-57 aren't required if you set the pullups to on. Pinmode(xx, INPUT); DigitalWrite(xx, HIGH); will set the internal 20k resistors and achieve the same thing. Depending on the gain (Hfe) of transistors Q4-6 you might want to drop the R51-53 down to 4k7 or 2k7 to ensure you fully saturate the C-E at 100% PMW. And don't forget the series resistor on the RGB leds Mark

mcb1 · Answer

Looking good. I'd change the 10uF to 1000uF (or even larger) since the 5v is also supplying your RGB leds which are 320mAx3 (960mA) (A rough rule of thumb is 1000uF per Amp) For R1-3 you may wish to use a darlington transistor that is capable of 500mA ie MPSA13 or MPSA14 which have a gain of 10-20,000, then you can use a 10k resistor. Try to keep your current paths seperate, ie the ground for Q1-3 should go to the supply, the ground for the ATmega 328 should go to the supply and both join at the supply point. A bit like keeping heavy traffic from residential streets but joining them at the motorway on-ramp. Your FTDI ground should go to the ATmega. The idea is to keep any switching currents from influencing the processor. Most of the ccts I've seen also have a 10k to +5v from the RST pin, and use a 0.1uF to DTR Without it it can float, and possibly reset when you don't expect, or not always reset. (Arduino Pro shown below) Mark

16 RGB LED's in parallel controlled by atmega328 PWM pins for pc case mod. (Updated)

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