Atmel AVR1923
11
8394B-AVR-02/12
V
0
:
Display voltage (contrast control).
⎟
⎠
⎞
⎜
⎝
⎛ +
Ra
Rb
1
: Voltage regulator internal resistance ratio.
V
REG
:
Internal fixed voltage supply typically 2.1V.
α
:
Electronic volume level, 1 to 64 are possible values:
The recommended configuration for the display is to use
5
.
3
1
=
⎟
⎠
⎞
⎜
⎝
⎛ +
Ra
Rb
because it
will center the adjustable voltage range at 6V which is the typical setting for this
display. Recommended values for
α
are listed in
Table 5-6.
Recommended electronic volume configuration.
Electronic volume
register value (
α
)
Display supply voltage V
0
[V]
Contrast
20
6.44
Too strong contrast
21 6.40
22 6.35
23 6.31
24 6.26
25 6.22
26 6.17
27 6.13
28 6.08
29 6.03
30 5.99
Optimal
setting
31 5.94
32 5.90
33 5.85
34 5.81
35 5.76
36 5.72
37 5.67
38 5.63
39 5.58
40 5.54
Very
weak
contrast
The display backlight is controlled by a FET which is by default in an off state but it is
possible to turn the backlight on with the Atmel AVR XMEGA by driving the gate of
the FET high. On the XMEGA pin PE4 is connected to the gate of the FET. The pin
PE4 is also an output of an on-chip timer module and because of that it is easy to do
dimming of the backlight by using PWM.
