Protonerd
commented
8 years ago Hi Vulkan1, The PWM value determines the voltage at the PWM capable output, i.e. if you set 100, it is 39.2% of the 5V (or generally speaking the voltage the pads are supplied with). If we stay with 5V, it means 1.95V on the gate of the mosfet transistor you drive your LEDs with. But it's not the same as your voltage over the LEDs!!! The reason is that the channel resistance of a mosfet is not a linear function of the gate voltage and different mosfets have different threshhold voltages and Idd vs. Ugs characteristics. Therefore the topic is more complex than simply taking a value. Therefore the rule of thumb is: select a resistance to limit your current such that even the full battery voltage will not harm your LEDs. Then you can even go up to 255 PWM value without any risk. If you do not want to do that, then you have to characterise your setup (the whole chain from PWM through mosfet to the LEDs)
Vulkan1
jbkuma
Hi, first of all I want to thank you so much for this awesome resource, your making a dream of mine come true. On the business end I want to make sure im correct in doing this and then ask my questions. Setup wise I have altered the config.h file and made #define LUXEON un commented and commented the other 2. I have left the color stuff as I assume that the "48" colors means 48 different colors picked evenly throughout the spectrum.
I have gotten to the MAX_BRIGHTNESS and for obious reasons its my concern as I don't want to burn any LED's. `/* MAX_BRIGHTNESS *
define MAX_BRIGHTNESS 100
` I don't know that the 39,2% is. and with 255 being the max, can I assume that is 100% of my batteries power (being 7.4v). If using the luxeon star, my red LED will have a max voltage of around 3.3, therefore I would want about 2.9volts to each pin. this being around 40% of total voltage, ill need MAX_BRIGHTNESS 99. I can then leave MAX_BRIGHTNESS at 100?
last question is with your diagram and the transistors, your diagram has all transistors leading to a board labeled BLADE MALE, and you show only one LED attached. @pin 8 of the BLADE MALE is the voltage input that goes though the LED, and then to the transistor. In my case I would run all the Vin's to the LED's of the luxeon star from pin 8 and then the - of the leds to the transistors of pins 3,5,6 @the arduino.
If I need to clarify anything please tell me, my explanations can be a but fluffy