Realist Viewer Modification for Extended Lamp Life

[P3D <s.spicer@xxxxxxxxx>]

I finally got around to implementing a scheme to reduce the surge current
that occurs when the lamp in my Realist viewer is switched on. If all goes
well, this may end up extending the life on the 2.5V/0.8A halogen lamp I
use (powered by two NiCad D cells).

I modified the switch so that one switch contact always comes into contact
with the contact ring under the red button _first_. To do that, a washer
under the mounting point of the contact worked in my case. Then I connected
a resistor from the ring contact to the other fixed contact (you could do
that by either installing a third fixed contact, or by soldering directly
to the top of the ring).

So now, the initial depression of the button results in a dim lamp glow as
the current is limited by the resistor, and a full depression of the button
gives the normal lamp brightness. By starting the lamp with a limited
amount of current, I should be able to extend the life of the lamp. However
it will take a while to verify that. ( I used a 1.5 Ohm/1Watt resistor, as
that is what I had to hand, but something a little higher may be more
appropriate.)

I do not enjoy drawing ASCII art, but here goes:

                            Contact Ring under red button
                             |
                             |
                             v
                      \      /----1.5 Ohm---
                       \    /     resistor  |
                     \  \__/                |
                      \                     |
                      /       /             |
                     |        \             |
                     |         |            |
                     |         |            |
           o---------|         |------------------o

                    ^^^^
                 Raise this
              switch contact
       (eg: put washer underneath)


At the same time, I got all my battery and switch contacts in two viewers
silver-plated to eliminate the lamp flicker I was getting from poor
contacts (cost was about US$7.50 per viewer). I hope that works out too.

Steve Spicer
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