key debouncing elimination with hardware

[chintesh]

hey guys i have read about the key debouncing concept and methods to remove it with the help of software by increasing the delay but if i want to remove it with the help of capacitors then what values of capacitors and resistors should i use?

 

[khetanikrunal]

you can calculate yourself using RC equation

example
For 5msec delay,
If Vdc=10, R=100E then C= 10uF

 

[jpanhalt]

These two references have become classics in hardware debouncing:

Debouncing
Debouncing Part 2

John

 

[srikanth1555]

Switch Debouncing - The Lab Book Pages


check out dis...

 

[qdnboy]

Hi all, regarding the RC debouncer (attached), in choosing the value of R2 for this, the author of this Debouncing Part 2 page originally chose 180K for this, but when he considers there's leakage current from the 74AHCT14 hex inverter of 1uA from the input, he up the cap value and changes R2 to 18k instead. I don't understand the mechanic for this, does it mean that the hex inverter is actually sourcing 1uA which goes through the R2 resistor to ground?

 

[jpanhalt]

That is what Ganssle is saying.

Source: Ganssle, part 2, just before the diode circuit.
But. the analysis ignores the gate's input leakage current. A CMOS device like the 74AHCT14 dribbles about a microamp from the inputs. That 180K resistor will bias the input up to .18 volts, uncomfortably close to the gate's best-case switching point of 0.5 volt. Change C to 1 µF and R2 is now 18K.

I don't understand your question apart from that.

John

 

[qdnboy]

So, when it says "74AHCT14 dribbles about a microamp from the inputs", does that mean the 74AHCT14 is demanding the current (sink) or giving out the current (source)?

 

[jpanhalt]

Here is a section form the datasheet directly:

The three columns represent minimum, maximum, and maximum at 125°C. I interpret that the positive current is sourcing.

John