On Mon, 5 Apr 1999 13:03:37 -0500, Jay Maynard <jmaynard@xxxxxxxxx>
wrote:
>On Mon, Apr 05, 1999 at 12:09:47PM -0400, John Hermanson wrote:
>> Modifying the OM-1 meter with the proper diode gives you a dead on
>> reading at all light levels if used with the silver oxide battery. This
>> mod essentially builds the MR9 into the camera.
>
>What *is* the proper diode? It would seem that a 1.35V Zener would be the
>Right Thing, but they don't make those that I've found...
As far as I know (from an earlier discussion) a certain Schottky diode
will cause the needed 0.15 V voltage drop.
I have even seen a description somewhere of a home made adapter which
incorporates this Schottky diode. I have never seen the MR9, but it
probably will be like this one, at least electronically.
I will try to describe it in my best English....
The base of the adapter is a round piece of printed circuit board with
copper layers on both sides and with a diameter equal to that of the
infamous mercury cells (so it will fit into the battery chamber of
the OM-1)
One hole needs to be drilled though the PC board, to take one of the
wires of the Schottky diode. The hole must sit eccentric, as much as
possible near the edge of the board. The Schottky diode must be placed
on the top side of the PC board, with one wire through the drilled
hole (mind polarity!). This wire must be soldered to the bottom of the
board, and must not make contact with the top copper layer. The other
wire of the Schottky diode must be soldered to the top. Cut the wire
ends as short as possible.
The Schottky diode must leave room for the silver oxide cell to sit
next to it with its negative bottom contacting the topside of the PC
board. The positive top will make contact to the cover of the battery
chamber, as usual.
Result of all this is a series connection of the silver battery and
the Schottky diode. It is a pity I can't make a drawing of the thing
(or even better: a photograph - but I have never contructed one
myself. I probably will have to, now mercury cells are going to be
banned in Europe too...
If anyone feels himself challenged to make a few of these in series I
will be happy to receive one and make that picture ;-)
Best wishes from Holland
Frank van Lindert.
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