22 Feb
2000
22 Feb
'00
9:35 a.m.
I have an
embedded computer which has four user
readable DIP switches on it. Board is running
at 3.3 volts. I want to be able to distinguish
between 7 possible SPST switches being closed
(one at a time) or all being open. I thought
If those SPST switches could become 2 and 3 pole switches, the problem is
trivial to solve.... "OK.
I'll just convert the single switch event
to a binary number by hooking it to the appropriate
pins on the DIP switch. Then I'll prevent the
multi-bit numbers from cross feeding the single
bit events by putting diodes in." But, the diodes
have too much resistance for the board to see the
switch as closed. The single-bit switches, 1, 2
and 4, read just fine.
The current involved is presumably small, so the problem is the 0.7V
forward drop of the silicon diodes.
You might try using germanium (if you can find them) or shottky diodes.
They should have a lower forward voltage drop.