Control the LEDs from I2C in order to control the max intensity

[lpatiny]

Currently we need to tune manually the led resistors to get all the range of the spectrophotometer. We should do this by software:

• MCP445x or MCP444x : digital potentiometer
• could select a 5k, 8bits like MCP4452. This means that we can control the resistor by step of 25 ohms. Even for UV it will be ok (need to take care of the program in order to put a minimal resistor otherwise we will burn the chip)

[lpatiny]

Should work and much cheaper than digital resistor