Shift Register for input

[erikbonthuys]

Can functionality be added to use shift registers for input 74hc165 or CD4021B
http://www.arduino.cc/en/Tutorial/ShiftIn

[rwaldron]

cc @soundanalogous

Jeff, this is probably in your wheelhouse :)

[soundanalogous]

I had proposed a couple of ways to do this for Firmata a while back:

firmata/arduino#64
firmata/arduino#51

The tricky part is different shift registers have their individual quirks. Some have a latch, some don't. Some need a low byte first, others a high byte first. If you look at #64 above you'll see some of the variations... and that implementation doesn't even cover all of the possible variations such as fractional byte shifting. In that proposal I was trying to hide as much of the complexity in the implementation as possible. The other proposal (#51 above) required more work (and knowledge) by the user of a particular register but would ultimately be more flexible. Additional constraints such as only being able to shift in a byte at a time could also help keep things simple (and flexible). I was trying for a multi-byte shift in/out protocol but the is just way to much variance to accommodate.

Comments are still welcome on either proposal. Perhaps I'll add another that constrains shifting to 8 bits at a time (so one Firmata message per 8 bits... you could still 16, 24, 32, etc bits each chunk of 8 would be a separate Firmata message).

[dtex]

Hi @erikbonthuys,

Johnny-Five contributors and maintainers are loathe to close issues where someone has a need. We don't want anyone to ever feel that we don't care, but we just haven't gotten to this feature yet. Rather than leave it languishing as an open issue we have created a Requested Features page and added your request for these two expanders there.