On Sun, 20 Dec 1998, Michael J. Ghormley wrote:

> which gives 25 ohms Ron at 4.5V.
>
> I also would be interested in any ideas of the group.  Any pointers to
> DIP/SIP-package switches with a lower Ron?  Other voices of experience
> out there?

imho, the Ron should not be a problem for this application. Micro
miniature switches in consumer equipment often use conductive plastic
and/or rubber switching elements and show up to 470 ohms Ron. It also
depends on how hard you press (I've played with this ;).

If there are serious space constraints a SMT PNP transistor will usually
work here. It is connected between the scan and the read line directly on
the back of the switch (C & E), and a thin wire connects the base to the
external base resistor. This assumes a HIGH driving scan line. A scope is
required to make sense of the signals beforehand. A NPN transistor is
required for LOW driving scan lines. Obtaining a copy of the schematic
diagram helps a lot (easy with Sony).

Also, using a micro miniature connector avoids having to drill holes etc
in the apparatus. In a pinch, a bar of SIPP machined IC sockets can be
epoxied inside the apparatus, female side outwards, after small (0.8 mm)
holes were drilled through the case in a suitable place. The mating
connector is a similar strip of sockets with long pins with a ribbon cable
soldered to the female side of it. Clip off a pin for keying (and don't
drill the corresp. hole).

The base resistor can be as high as 100k, I often use 47k in this
position. If the apparatus controller and the driving controller operate
at different Vdds extra precautions are required to make sure that the
switches turn on and off as required.

hope this helps,

Peter