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Is there a chip that is just a parallel in / serial out shift register but with integrated internal pullups?

I could use a full-blown I/O expander but I really just need more momentary button inputs. I don't need outputs and I would rather not bother adding resistors or with writing commands to initialize the chip.

  • Have you considered using a button matrix instead? – Ignacio Vazquez-Abrams Jul 20 '16 at 0:05
  • No but unfortunately that doesn't really help me. Not unless there were a chip that automatically handled the decoding and output serial. – squarewav Jul 20 '16 at 0:45
  • You say "more", which presumes that you're already handling some. Just change how they're being handled. – Ignacio Vazquez-Abrams Jul 20 '16 at 2:24
  • Probably doesn't exist. forum.arduino.cc/index.php?topic=162710.0 – Gerben Jul 20 '16 at 11:27
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Logic integrated circuits such as shift registers normally do not contain pull up resistors on their input(s). This is because they are normally connected to a totem pole driver. Such a driver eliminates the need to avoid floating inputs.

Also, pull up resistors require current when the input is driven toward the opposite power rail. Even though adding internal pull up resistors may not change the overall behavior of the chip, designers will avoid parts if they unnecessarily add to the over all power demand.

Based on your comments and your question, consider an old ps/2 keyboard. It is essentially a switch matrix with a built in decoder chip which may fullfill your requirements. The chip scans the switch matrix, debounces the switches and converts button presses & button releases into a serial stream of data.

Added later...

Here is a description about connecting a ps/2 keyboard to an Arduino. Included are schematics, code examples and supporting library.

(USB keyboards are not well suited for this purpose as they require a USB Host. As most Arduinos do not have this, a USB Host shield is required.)

  • I think you mean debounces... ;) – Majenko Jul 20 '16 at 7:04
  • That's funny! I should never answer a technical question on a tablet. I'll change it. Thanks. – st2000 Jul 20 '16 at 11:57
  • I guessed you had. Mine tried to change it in exactly the same way. Android? – Majenko Jul 20 '16 at 12:15

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