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Checking multiple switch states

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#1 alanglynsmith

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Posted 15 November 2013 - 07:20 AM

Hi anyone any ideas or suggestions of how to use a LabJack U3 HV to check up to 500 different switches in a 20x25 matrix to see which are on and which are off?


I initially thought 32x32 but 1024 is way too many switches to wire up so going on the same principle of 32 x 32 but highest reached will be 500


i.e. we need to identify each switch, check its state and save that data. Can be done serially or inparrallel not bothered. Although parallel would probably involve quite a large number of extra chips 


(we are trying to develop a mat that can see a pattern from a water spray) this will allow us to automatically pass or fail a particular nozzle.


Many thanks


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#2 LabJack Support

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Posted 15 November 2013 - 10:31 AM

You could use I/O port expander chips that provide 16 digital inputs each and talk to the U3 using SPI or I2C.  We have used the MCP23S17 SPI IC, but any should work:




You would need 32 of these.  Seems OK, but we would need to think about the limit for number of I2C or SPI chips.

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