PWM controlled RGB strip hardware white balance

Hello, I have a working RGB strip control setup as described here http://learn.adafruit.com/system/assets/assets/000/002/692/medium800/led_strips_ledstripfet.gif?1396785823 . The white balance is bad. White is about 255, 180, 90 in RGB. I would like to use the full resolution of the PWM output and have 256 steps in each channel. Is it possible to regulate the voltage after the PWM in some way so that I can achieve white at 255,255,255 RGB ?

Your link points to a 12V RGB strip. It is powered by an arduino that does not have 12V available, but rather 9V. Have you tried 12?

It is possible to supply each color with a different supply voltage and/or a different current limiting resistor for each color, but not with that light strip. It would need more connections to do either.

-fab

No you can not fade the strip all the way to zero using pwm and keep the same colour balance just using software. You can play about with seriese resistors in the green and blue so you get a natural colour balance but the resistors have to take all the current and so need to be a high power rating.

I disagree with fabelizer on this point.

The RGB strip has an external 12V 5A PSU. I am using the transistors to control it. So the diagram is wrong in that sense. The 12V comes from the PSU and they all have common ground. The quick fix I am using now are 3x 10k potentiometer wired as a voltage divider connected between the arduino PWM output and the transistors. Each pot is wired 1-ground, 2-transistor, 3-PWM. The side effect from this is that the RGB strip color is not equally distributed. The end of the strip seems to be underpowered sometimes.

Tantric: The quick fix I am using now are 3x 10k potentiometer wired as a voltage divider connected between the arduino PWM output and the transistors.

:astonished: :astonished: :astonished:

One way would be to use separate values fed to the PWM to achieve what ever color balance you want and then use the mapping command to map those values each to 0 - 255 etc. If you do it this way you don't have to buy more components to regulate the current and you can change things later if you feel the colors are off etc.

jarrod0987: One way would be to use separate values fed to the PWM to achieve what ever color balance you want and then use the mapping command to map those values each to 0 - 255 etc. If you do it this way you don't have to buy more components to regulate the current and you can change things later if you feel the colors are off etc.

Yes that is what he is doing but he can not keep the colour balance and fade all the way down because you run out of resolution on the PWM at the lower light levels so the balance is all over the place..

The quick fix I am using now are 3x 10k potentiometer wired as a voltage divider connected between the arduino PWM output and the transistors.

That is not a quick fix that is a silly kludge, it is not stable and will not work, apart from that it is fine.

. So the diagram is wrong in that sense.

Hey we love getting diagrams that are wrong, it wastes time and produces inaccurate answers just what we love. ( do you do irony? )