You can do this with just two lines. A diode and RC on the
'595 load line coupled from the clock. Every clock low (dis)charges
the R/C. Once the clock stops, the RC charges up and trips past
the load threshold (or discharges if I've got the load polarity wrong).

We used this technique to built a 128 bit S/R for controlling a train
layout.

And if you want to be really clever you can do it all with just
ONE line by varying the down time of the clock and getting the
data from an R/C decay of the clock to data pin. (you need about
3:1 for data and 8:1 for load for good reliability)

Jeszs wrote:
>
> I have used the 74HC595 shift register.
>
> >From your PIC:
> 1 line for serial output
> 1 line for clocking the serial output into the chip
> 1 line for parallel output latching
>
> Voila, 3 outputs converted into 8, 16 or more number of outputs.
> You may want to have an extra line for output reset.
>
> --------------------
> Jeszs Gonzalo
> Lesn (SPAIN)
> --------------------
>  xm6   0~   +-}J& )m}8^ +-1joz7

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