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Today at Atelier Kaz - ex-Honda R&D, F1, Indy/CART engineer

CCU Illumination

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2 Comments
by
Kaz-kzukNA1
, 02-10-2012 at 12:14 PM (3903 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
Categories
A/C CCU Board Service , Electronics

Comments

  1. greenberet's Avatar
    Dear Kaz,

    Personally, I’d be happy if the clock, CCU and radio lights didn’t go to the dim level when the parking lights are turned on but only when the main beams are turned on. Do you think that would be easier to accomplish? Is there a little “dim” wire in the light switch that could be pinned into the main beams position instead of the parking light position?
  2. Kaz-kzukNA1's Avatar
    Hi, greenberet.

    It can be done using several different methods but I don’t think it’s practical considering the time required for the modification as well as putting everything back to the original state when you want to.

    I started looking into this since I use the position light as DRL that I’m planning to install in the future so when it’s done, I must put everything back to how they used to be, so any modifications have to be minimum.

    The aftermarket DRL system from major manufactures such as Philips monitors the changes in the battery voltage when the engine has started (ACG starts to generate power) and automatically turns the DRL On. Obviously, you don’t need to touch the lighting switch so the illumination at all three devices (Clock, CCU, Audio HU) stays at their normal brightness.

    Although you are no longer going to have the position lights (EU regulation), if you turn the lighting switch into ‘position/small’ or ‘dip beam’ position, the illumination will be dimmed which is probably better when driving in the night although it didn’t bother me even they were at full brightness while testing my modification.

    As major manufactures already developed and tested the products and guaranteed to meet the EU regulation, I will just buy it instead of trying to create something from scratch.


    Having said this, you could just create a simple circuit to do the same if you don’t want to install aftermarket DRL and switch on the position light without touching the lighting switch.

    However, position light circuit is at the downstream of ‘tail light relay’ which is the source of the illumination control lines for the above three devices.

    Since they are connected in parallel together with the position light, you must modify the existing wiring and create stand alone circuit for the position light. It’s easy because you just need to cut two wires and separate them from rest of the downstream of the tail light relay but I don’t like cutting the chassis loom…..

    Simply powering up the position light without separating its circuit from the rest will dim the illumination on all three devices even if you haven’t touched the lighting switch.

    Kaz