CCU Illumination
by
, 02-10-2012 at 12:14 PM (3918 Views)
While working on MX5 engine, I was looking into the way on how to
disable the dim function on the illumination at CCU display (VFD).
Can’t remember how it used to be when my NSX was new but
as many owners experienced,
it is almost impossible to see anything on the display of Clock, CCU and
Audio Head Unit during the daylight when the small side light is
switched on.
As reported earlier in this blog ‘Clock’,
we can easily disable the dim feature on the clock.
Just pull out one wire and insulate it well to avoid any short circuit.
The CCU is bit tricky because the two light valves on the
display controller board go through the illumination control circuit that
will change the brightness variably.
These two light valves are used as the back light for the two big round dials
at the side as well as for the push buttons at the bottom with
green/amber LED inside.
These LEDs are not part of the illumination control circuit so
they don’t have variable brightness and they will just dim when
the light switch is operated.
The display is ancient VFD type so the driver voltage changes the
brightness of the segment.
On my CCU, it’s using OKI M5267B as its display driver.
I don’t know whether it is the same on the later model.
The output driver is controlled by the Pin 27 of this IC and when
the display is at full brightness, it will be at 5.0V whereas when the
light switch is operated, it will be down to about 0.5V resulting in
lower fluorescence and thus, the display will dim.
The power source to the LED is common to all three LEDs at the
push buttons and as it was under the VFD module itself,
I couldn’t see the actual parts but looked to be controlled by just a
single transistor output.
So, if you want to disable the dim feature at the display and LEDs but
want to keep the variable brightness for the back light,
you just need to keep the Pin 27 at the VFD driver at high level and
disable the base current at the transistor controlling the power to
the LEDs.
I don’t like the idea of putting additional switch to
enable/disable the dim feature so considered writing short software
using PIC micro with simple circuit so that by pressing and holding one of
the push switch such as Re-Circ at the front panel for 5sec to toggle
between enable/disable of the dim feature.
Not enough spare time for this so may be in the future.
One thing I noticed was that if both light valves were dead,
the display and LEDs were always dimmed even the light switch was not
touched.
Not great circuit design…..
Any way, I would like to test this under several different
driving and lighting conditions using my NSX and once I’m happy with
the result, I’ll post the detail.
Didn’t have time to look into the audio head unit but since it doesn’t
go through the Illumination control circuit and the display module is a
stand alone parts and the ribbon cable just slides out with ease,
should be not too difficult to achieve the same.
Kaz