Its to go into a reed relay telephone switch from the 1960s. If something went wrong it would print out what equipment was at fault by burning upto 90 lines onto electrosensitive paper. I need to take the 50v from each "pen" and log which ones are live. Im sorry if Im not giving full details but some things you mention I havent a clue what they are. Like a shift register for example? Thanks for the help. Sent from iPhone On 29 May 2010, at 11:28, Michael Watterson wrote: > Andrew Wood wrote: >> Ive been doing some research into possible solutions and have found >> references to a MAX4626 "analogue switch" which to me looks like a >> solid state relay - it says its the size of a grain of rice. >> >> What Im contemplating is using 90 of these arranged in a matrix >> with 9 >> columns and 10 rows per column. Each column would share an output >> pin >> from the PIC which I shall refer to as "column select" This would be >> wired in parallel to the COM pin of the MAX4626. The IN pin would go >> to the wire I want to sample which has a voltage divider on it to >> drop >> it to 5v. >> >> The PIC then tests each column in turn by switching on the >> appropriate >> column select wire, thus applying 5v to the COM pin of all the >> MAX4626s in that column. If the wire being sampled is live it will >> put 5v on the IN pin and the solid state relay will close. The >> prescence of 5v on the NO pin of the 4626 will indicate the wire >> sampled is live. This will allow me to sample the 90 wires using >> only 19 i/o pins on the PIC. >> >> >> Does that sound reasonable? >> > no. an 8 way switch is better CD4051 > 3 address wires out in common paralleled for all twelve switches. 12 > inputs. Total 15 pins. > or if you add a 16 way 4 bit decoder IC, to drive Inhibit lines, > then 1 > input and and 7 outputs. > > or use a matrix of opto-isolators 12 x 8 = 96 = 20 pins > > 9 x 10 can be done too, but the code for 12 x8 is simpler. > > or Russell's serial shift register > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist