Switch Debouncer?

[Electroenthusiast]

I'm using 74279 IC for SR Latch...
I want to make it work as a switch debouncer,
Let me know how to calculate the value of 'R' in the Diagram,
so that I'll be able to run the IC properly.



I know that i can use separate IC's for it, but since i hav 74279 i want to use it for application.

 

[MikeMl]

It is just a pull-up resistor. 1K to 10K would work for 7400 series; 10K to 100K for CMOS.

 

[Hero999]

It doesn't matter, it's a pull-up resistor, just use a 10k resistor.

 

[Electroenthusiast]

Thanks...but Why 10K ?

I want to know how to determine it? (if i use someother IC)

 

[MikeMl]

Thanks...but Why 10K ?

I want to know how to determine it? (if i use someother IC)

Look at this data sheet. Note Vih and Iih for a given logic type.

e.g., Vih = 2.4V when Vcc=5.0V. Iih is 50uA. Therefore, the maximum value that a pullup resistor could be and still meet the Vih/Iih limit is (5-2.4)/50u = 52K. Any pullup resistor that is 52K or less will work. How low you make it is determined by how much power you are willing to waste, and what is switching it low. Hint, a push button switch is probably rated at 1A, so the lower limit is 5Ω.

 

[Electroenthusiast]

Thanks You