How to connect the Osc and Debounce pins for 74C922 keypad?

[louislu]

i planning to use 74C922 for my proj.it's for password verification.anyone know where shl i connect the pin Osc and Debounce? how to connect? i would like to have a easy and simple keypad encoder.....is this 74C922 good enough for me...thanks in advance...

 

[papyaki]

74c922 pdf

Hi,

You must connect two external capacitors, one on Osc pin and the other to Keybounce Mask pin.

See the datasheet page 5 for the values of Cosc (connected to Osc pin) and Ckbm (connected to Keybounce mask pin).

h**p://www.supremetronic.com/spec/74c922.pdf

* = t

 

[louislu]

74c922 circuit

thanks...i found the data sheet.and how bout the circuit connection?is it follow the block diagram on page 4.n wat is the dirrerent 0.01uF and 10uF for capacitor of OSC?is it the different in scanning the keyboard frequency?

 

[papyaki]

keybounce of 74c922

Hi,

At cOsc pin, for 10nF, the scanning frequency is about 6kHz, for 100nF it is about 600Hz, and for 1uF it is about 60Hz.

For debounce, the period is about 1mS for 100nF, about 10mS for 1uF, about 100mS for 10uF and about 1Second for 100uF.

 

[Nomad204]

Re: keybounce of 74c922

Hi,

At cOsc pin, for 10nF, the scanning frequency is about 6kHz, for 100nF it is about 600Hz, and for 1uF it is about 60Hz.

For debounce, the period is about 1mS for 100nF, about 10mS for 1uF, about 100mS for 10uF and about 1Second for 100uF.

In datasheet, C(KBM) = 10 C(OSC).
So, I usualy use C(OSC) = 100nF, and C(KBM) = 1uF. It work very well