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ok here goes, Iam trying to build a device to test nurse call room controllers, these are basically 8 port boards with rs485 linking (have software for this, what i need to do is test these, to do this i need to close a contact (call) for 1 second then 5 seconds later i can cancel that call by closing another contact to do this i need to automate 16 switchable outputs, 1 to activate it and another to cancel it

i was hoping an Arduino USB Board might be able to handle this?

i used to judt play with 555ic and 4017 ICs untill i got what i needed but i thought i would move into this century and make myself learn something new. .

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If I was doing this, I'd go for a couple of 74373's. These are latches, which can either pass through a signal, or hold it until needed.

Each one will hold the state of 8 pins, so you need 8 pins for your data, and 2 pins to select each bank. That's a total of 10 pins so will fit on a Duemilanove, and avoids the difficulty of SPI.

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I think arduino has 20 I/O? So you don't need any extra expander chips if all you need is 16 switches. It may still be a good idea to use the expander chips, in case you want to add something in the future, or a LCD display or status LEDs, or input buttons etc.

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  • \$\begingroup\$ i have one on order now, must play, must play \$\endgroup\$ – Rod Aug 16 '10 at 8:06
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You can get your 16 outputs by interfacing two 74HC595 shift registers (eight outputs each) to the Arduino using SPI. The SPI function isn't supported by the Arduino, so you will have to write the code yourself.

[Edit]

Here is some SPI code.

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  • \$\begingroup\$ cool i'm lookig into it as an option now thank you \$\endgroup\$ – Rod Aug 16 '10 at 0:02
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Are the inputs of the controller in question compatible with TTL? If so (and they likely are) then the arduino is a perfect fit. If they are not, for instance if they want a 12 volt level to switch on, or if the switches use some non-dc signal, then you will need some sort of relay setup.

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  • \$\begingroup\$ great ideas everyone, thank you very much, when my board arrives i will be able to set it up as needed. you are appreciated. \$\endgroup\$ – Rod Aug 16 '10 at 14:42

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