In this case I do not see the reason for the Open C. illustration, often the input is a Opto isolator and they indicate that either a contact closure or sinking device input (O.C.) can be used.
There is no real reason to go with a Semi Con unless it was an outboard opto for isolation reasons.
Max.

 

I will try to eliminate the open C and directly connect some switches to ground.... wonder if that will work...

 

There should be no reason why not, take the inputs to common or GND.
Max.

 

Hello again
I thought I was done with this thread but something came out.

As you know I am using a SN74LS07 for open C and 74HC14AP for Schmitt inverter. I have their datasheets and I have made the board and it works without problems.

Now, one of the assistants here have raised two issues with my design:

1) Each IC needs a capacitor between 5V and ground, he says. Is this true? I suppose this is what is called decoupling capacitors but how to calculate the appropriate value of the cap??

2) Unused pins. He says that all unused pins of the ICs should be pulled up (or down??). Is this true??

Some advice will be greatly appreciated

 

A 0.1μf decoupling capacitor is usually sufficient. To avoid any problems it is usually recommended to take unused inputs to power common.
Max.

 

He says that all unused pins of the ICs should be pulled up (or down??). Is this true??

Unused input pins only.