Switches as inputs

Thread Starter

Gadersd

Joined Dec 8, 2012
98
I am going to use switches as inputs to my registers. The problem is that I am using ttl ics and cannot use pull down resistors to prevent floating inputs. I know I can use pull up resistors, but then the default value will be 1 instead of 0 with a pull down resister and I need the default to be 0. How can I use a pull up resister without having to invert the outputs?
 

FrozenMel

Joined Aug 23, 2011
34
So just to be sure, you want to use a register that has a TTL input and want your normal state to be 0 and your switched state to be 1?

If that is the case, and you aren't worried about power loss too much, you could use a high value pull up resistor and have the switch normally closed, connected to ground. Then when you flip the switch, the ground short is disconnected and the pull up resistor takes over changing the logic level from 0 to 1.
 

MrChips

Joined Oct 2, 2009
30,720
What's the fuss about the default being 1? Use a pull up resistor and reverse the logic in the code.
 
Last edited:

absf

Joined Dec 29, 2010
1,968
If you like, you can use the more popular 74HCxx or the 74Cxx series of TTL. Pull down is allowed on these devices.

Allen
 
Top