IMPORTANT:
* All the parts with reference number bigger than 9 should not be installed
  (i.e. parts with reference numbers 10, 11, ... should not be installed).
  Leave their pads unconnected.
* Two pad pairs on the PCB are marked as NoAVcc. Jumpers should be installed
  there. Notice that one pad pair is also used for L10 (BEAD). At that
  location it is actually a replacement of the BEAD with a jumper.

The other option is to install all the parts and not to install any jumpers
 marked as NoAVcc. This option should provide more stable output from the
 photo-transistor and more stable AVcc and therefore more stable data from
 DAC (connected to the photo-transistor). This may be helpful but it is
 probably not much useful since the firmware must average about 10 (or more)
 measurements of data from the photo-transistor. The reason why this must be
 done regardless of DAC stability is that we often use light sources which
 actually flicker at the main frequency (50 or 60 Hz). We need to measure
 the light intensity more times during the mains period (about 20 ms) and
 average the values to get the proper illuminance. This averaging should also
 eliminate the most of the DAC instability.

Note: When capacitor C11 is installed then the photo-transistor can get spikes
 of current bigger than 20 mA (up to about 100 mA) when it is exposed to the
 direct sun. Not even studio lighting can do this but direct sun can. This
 current spike can potentially fry it. When working on firmware make sure to
 use DAC and ramp up the photo-transistor curent slowly.