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I am currently working on a wireless home automation system. The system is connected to a wireless network in the home via the ethernet cable connected the ethernet shield and router. Hence, I need more pins on the Arduino to connect the appliances to be controlled in the home.

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You can control a shift register with shiftOut or bit-banged SPI.

My page about SPI has a small library that does bit-banged SPI.

It is also possible to control a shift register using the same pins (MOSI/MISO/SCK) that the Ethernet interface uses, as long as you use a different SS (slave select) pin for your shift register. This may not be practical if the Ethernet card is active all the time. It is probably easier to do the bit-banged SPI or use shiftOut.

  • Yeah, if the Arduino has available pins to run a bit-banged SPI, it would likely be a bit safer overall. – WineSoaked Aug 11 '15 at 3:11
  • Not all shift registers have an SS pin. But that doesn't matter as long as you don't latch the data sent to the Ethernet shield. – Gerben Aug 11 '15 at 9:51

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