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Read 16 Digital Inputs with 4 GPIO?

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digi001

digi001

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I am looking to read 16 digital inputs using only 4 GPIO Lines.

This would be straight forward using an Encoder if i could guarantee that only 1 of the 16 lines can be active at a time. However any combination of these may be possible.
How could I accomplish this?

I think if I scan the lines with 4 Reads I should be able to decode this problem. Do they make chips to do this?
 

What is the MCU or processor you are using in your design?

You could implement SPI in hardware or software and use a SPI port expander, there are several available with 16 GPIO.

BigDog
 
I am looking to read 16 digital inputs using only 4 GPIO Lines.
Click to expand...

I think you can use SPI input shiftregisters for this one you only need to have 3 PIns to read all the 16 inputs or more..
 
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    digi001

    digi001

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ShftInExmp2_Schem[.jpgTwo cd4021 will give you 16 inputs(16 bit).
Arduino - ShiftIn
http://www.redrok.com/CMOS_CD4021BC_8-StageStaticShiftRegister_Fairchild.pdf

MCP23017 it is a GPIO expander and has also an open collector interrupt pin that is activated on port pins state chenge.
**broken link removed**
 
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