This is another case of making use of the 4 extra PCB’s that come with my order from China.  The board is designed so that it can act as a diffuser over the blue LED matrix, which even at it’s lowest PWM is pretty bright.  The circuit arranges component holes around the outside of the board, leaving a clear area in the middle for the digits to glow through.

The display is off in daylight and late at night/early in the morning.

In the past, when using an LDR to control brightness I keep a rolling average reading. This time I just treated the LDR value (in relation to a threshold) as a debounced “switch”.

Pins.h in the sketch has a schematic and parts details.

More photos:

Flickr Album

Arduino board:

Leonardo Tiny Atmega32U4

LED matrix:

8x16 Matrix LED Display Module