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