Hi,
I've been trawling and sent myself to sleep reading datasheets but someone here may know this already.
I want a simple method of polling 32 digital inputs using a single 8 bit port. - (simple and rubust is key! )
So... use 4 x 74HC244 (Non inverting input buffer with enable), 8 digital inputs go to each chip. Each chip has an enable pin, select and read each one in turn.. nice simple solution.
But I cant find a version with all the inputs on one side of the chip and the outputs on the other, thus giving a much tidier PCB layout.
I also understand that multiple 74HC244 can add to much capacitance to the bus. The digital states being read will be very slow (mechanical switches ) but I would still wish to select and read each chip each one at a decent rate.
Any Ideas?
I was avoiding using the 74HC574 but currently looks the most promising.
I could also use an input expander using SPI but I've already got loads of SPI devices and routing the tracks to so many devices could get messy.
John.
Alternative to 74HC244 extra digital inputs
- Jay Dee
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Re: Alternative to 74HC244 extra digital inputs
Ahh fresh look today.
74HC541 looks like a go.
> All inputs on one side, outputs on the other.
> Schmidt input behavior (Hi State at 3.15V [4.5V Vcc] Lo State at 1.35V [4.5V Vcc])
> Enable pin (Pull pin Lo to Enable)
> All pins are Tri-State when disabled (Off Bus)
> Easy to solder SOIC Package (1.27mm pin pitch)
> 2 to 6 V supply, nom 5V.
> Just 6ma output drive.
Will give this a go I think.
J.
74HC541 looks like a go.
> All inputs on one side, outputs on the other.
> Schmidt input behavior (Hi State at 3.15V [4.5V Vcc] Lo State at 1.35V [4.5V Vcc])
> Enable pin (Pull pin Lo to Enable)
> All pins are Tri-State when disabled (Off Bus)
> Easy to solder SOIC Package (1.27mm pin pitch)
> 2 to 6 V supply, nom 5V.
> Just 6ma output drive.
Will give this a go I think.
J.
- Jay Dee
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Re: Alternative to 74HC244 extra digital inputs
Oh forgot..
Texas SN74HC541DWR
Farnell 1607638
40p each or 23p for 10+
Texas SN74HC541DWR
Farnell 1607638
40p each or 23p for 10+
- Steve001
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Re: Alternative to 74HC244 extra digital inputs
Thanks for that one project i have lurking i needed 40 inputs (Ribbon cable tester)
will look into that later
steve
will look into that later
steve
Success always occurs in private and failure in full view.
- Steve001
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Re: Alternative to 74HC244 extra digital inputs
there is also a dip version
FEC 380817
Steve
FEC 380817
Steve
Success always occurs in private and failure in full view.