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One Raspberry Pi 3 B & Four IO PI expanders

The IO Pi Plus is a 32 channel MCP23017 GPIO expander for the Raspberry Pi

24/06/2017

Posted by:
NATechServices

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I took the time to search this topic before posting here for help, lots of great info to parse through.My project is to prototype a digital EICAS annunciator with LCD display. With up to 128 I/O.My first question is seeking recommendations or directions on how 4 IO Pi Plus expansion boards connect to one Raspberry Pi 3 B? Should I power each IO Pi Plus independently? I assume yes.The majority of signals are input only, with enough outputs to drive an LCD. If an input comes in, text is to display onto the LCD until it is manually cleared by a user.I've reviewed the video on how to assembly an IO PI plus board and see how the header connects to the GPIO. My assumption is these IO Pi Plus boards stack on top of each other and get chip selected via I2C address bits.Simple questions I suppose but would greatly appreciate an image or confirmation that this is the proper strategy. Also if there are any issues I should be aware of id appreciate any advice before buying parts.Thanks a bunch!

24/06/2017

Posted by:
andrew

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Location:
United Kingdom

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Hi

If you are using mostly inputs and the outputs will not be drawing much power then you can probably get away with powering the IO Pi Plus boards directly through the Raspberry Pi GPIO connector. Each of the MCP23017 IO chips on the board can supply up to 125mA to the IO bus so with four boards mounted to the Raspberry Pi the most power it could draw if you put the maximum load on every chip is 1A. As most of your signals are inputs it will not draw anywhere near that amount so the GPIO connector should be able to supply enough current.

The IO Pi Plus boards stack on top of each other. I would recommend using our mounting kits to hold the boards secure on top of the Raspberry Pi. As you are planning on stacking four boards it may be worth using right-angle IDC sockets on the boards with ribbon cables going to your other devices. We designed the IO Pi Plus to work with the right angle or straight IDC sockets but you can only use right angle sockets if you want to stack the boards as there isn't enough clearance for the straight socket and ribbon cable to sit in between the boards.

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