>As an alternative I have also used the I2C bus to control output devices (8
>outputs) PCF8574 if I remember correctly.  Each of the devices has 4
>addresses allowing 32 outputs from 2 control wires, in addition there is an
>"A" part that allows an addition 4 addresses giving the possibility of 64
>outputs from  the 2 wire bus.


Could also use eg 4094 or similar 8 bit serial load / parallel output shift
registers  chained together as required but these often have low ish drive
and MAY need buffers as well. eg ULN2803 etc. Advantage is only 3 lines to
control the whole array (clock, data, load). Care needs be taken with ripple
carry for large arrays.




RM