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Question about 74hc165 shift register  

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Royz
 Royz
(@royz)
Active Member
Joined: 7 months ago
Posts: 5
2020-04-19 3:54 am  

The example wiring diagram in the shift register presentation uses individual pull down resistors for each switch connected to the 74HC165.  Could not all the switches be connected to a single resistor which is then connected to ground, especially if only intend to use single switch at a time?


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Royz
 Royz
(@royz)
Active Member
Joined: 7 months ago
Posts: 5
2020-04-19 2:27 pm  

I suppose if you are going to use resistors, one could also string a series of them in a multistage voltage divider and connect switches at each junction point.  Then each switch would output a different voltage that could be fed to a single analog input.  Power, ground and one analog pin would be all that is needed and not 74 chip.  I assume this is how a keypad by ILS I saw on Amazon works?


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DroneBot Workshop
(@dronebot-workshop)
Workshop Guru Admin
Joined: 1 year ago
Posts: 628
2020-04-19 3:27 pm  

@royz

No, that wouldn't work, you would be literally shorting all of the inputs together!  Take a look at the schematic and you'll see what I mean.  The pulldowns keep each digital input low, pressing a switch brings the input high.

Posted by: @royz

I assume this is how a keypad by ILS I saw on Amazon works?

Yes, I have already covered that keypad in my LCD article and video, it uses one Arduino analog input. But, of course, that's a completely different subject!

😎

Bill

 

"Never trust a computer you can’t throw out a window." — Steve Wozniak


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