General Purpose IO Pins

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I need to put some universal IO pins on a unit. As they'll be connected to the real world they need some protection. Ideally I'd like them to work as...

1) open-collector outputs
2) digital inputs to detect an external DC voltage in the 5-24v range
3) digital inputs to detect switch closure to ground

Any thoughts?

My current doodle looks like this (ignore pin numbers)...

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#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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1) That should be an HC541.
2) R1 might need to be a bit lower to give a decent wetting current to any switch.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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I'd avoid using a zener and go for something like a transil that is meant for tranient protection. NXP have some nifty transient protectors in a sow20 package. That part number escapes me at the moment but you get 18 units in one package - smt only though.

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#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Total votes: 0

Brian Fairchild wrote:
I need to put some universal IO pins on a unit. As they'll be connected to the real world they need some protection. Ideally I'd like them to work as...

1) open-collector outputs
2) digital inputs to detect an external DC voltage in the 5-24v range
3) digital inputs to detect switch closure to ground

Any thoughts?

My current doodle looks like this (ignore pin numbers)...

That looks like it will work as open-collector output and is able to detect switch closure to ground, as there is the pull-up.

But because of the pull-up, it cannot detect if it has +24 connected or disconnected, as nobody pulls low when it is disconnected.

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Thanks Jepael,

not being able to detect if the 24v is disconnected isn't a requirement, only that it's 0v or 24v (actually 0v or 'more than 1/2VCCish').

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Brian Fairchild wrote:
http://www.nxp.com/products/auto... perhaps?

Or something like SN74S1053--lower TDP, but you get 16 series pairs instead of individual diodes, so it oughta be easier to route.

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BZA100 it is!