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Author Topic: What is an I/O Expansion Board?  (Read 2895 times)
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This is probably one of the stupidest questions asked here... but what is an I/O expansion board and what is it used for?

Is it used for testing software? Or for connecting between different interfaces?

I was told I will be working with an Arduino micro controller, joystick, lcd screen, servo, and an I/O expansion board for a project and that I need to interface them all together as soon as possible, but I can't figure out how the I/O board is used? Shockingly googling "i/o expansion board" returns very little information.

Thanks for the help!
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An input/output expansion board does exactly what it say on the tin.
A microcontroller has a limited number of pins, and hence a limited number of interfaces with the outside world.
An expansion board takes a few of those pins (typically I2C pins) and fans them out to even more pins.
Of course, there are usually trade-offs, like lower switching speeds (because of the I/O overhead of addressing and commanding the additional device)
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One IO expander chip I work with a lot is the MCP23S17 from Microchip.  It is controller by SPI (they do an I²C version too), which takes 4 IO pins, and provides 16 IO pins.  You can optionally use a 5th IO pin to act as an interrupt trigger, so the 16 extra IO pins can do change notification and trigger an interrupt on the Arduino when a change occurs on any of the extra pins.
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Hi, can you SEE any of the things you have been told about??

Boards that plug right on top of Arduino are usually called "Shields".

Maybe they mean something like the connection expansion shield often called a "Sensor Shield", like these: http://arduino-info.wikispaces.com/SensorShield

(These can also be used to connector to Actuators like LEDs, Buzzers, LCD Displays etc.)
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The centipede shield is a good example of an I/O expander. It uses an I2C interface as AWOL described and MCP23017 chips like majenko described smiley-wink
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Think I have a better idea of whats happening now... Thanks guys.

Maybe I am supposed to use the i/o board in combination with the joystick for interrupts as Manjeko said... hmm
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Verry possibly (i'm sorry i couldn't resist that one...)

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