On Wed, 25 Nov 1998 09:00:39 +1000 "Paul B. Webster VK2BZC" writes: > We've looked at this before, it often gets into multiplexing, diodes >etc. Consider PISO shift registers, (HC165, CH597 - whatever is >cheap), one per eight switches, mounted adjacent to the switches with a SIP >resistor pack for pullup. > > Board layout it thus dead simple. Only three lines (load, clock, >data) to the PIC, at least two may be shared with other functions, no >matter *how many* switches. I agree that this is a "dead simple" way of going. However, I believe that "The ideal design has zero parts", so I TRY to not add any extra chips or pull-ups to a design. A fair number of my designs have three BCD switches, so I use port B with internal pull-ups and 4 bits of another port with external pull-ups. This is all on a 16c74a. Of course, on smaller chips, or designs that need all those pins for something else, you're stuck either multiplexing with a tone of diodes or doing the shift register trick. I wonder how cost works out between using a PIC with enough pins versus adding a shift register with a smaller PIC. Another approach that has been mentioned on the list is to use the thumbwheel switches with a resistor network to provide a variety of analog voltages to an A/D input of the PIC. Anyone have ideas on a SIMPLE encoding scheme for this, possibly using a standard resistor network? Harold Harold Hallikainen harold@hallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]