Usage of Schmitt trigger NAND Gates


I have a question about your “Long Duration Timer” circuit, del20017 found here ..Long Duration Timer Clock


You have labeled U1 as a 4093. A 4093 is a NAND with schmitt trigger inputs, yet the schematic displays only NAND gates without schmitt trigger inputs. Which device did you intend? A 4093 or a 4011 (Quad 2 input NAND gate).

Mail from PB

Where mixed signals are at input both analog and digital 4093 is better. Like digital inputs after going thru a long cable the square wave gets deformed, 4093 refines it to a digital square again. When interfacing with input devices like switches 4093 is better as it works as a noise filter. Generally 4093(++) is an upgrade to 4011, i think it is a pin to pin replacement .

Digital Timers Counters and Clocks

In the circuit above U1C and U1D have to be schmitt trigger nands. U1B also needs a bit of wave cleaning. U1A can be 4011.


The 4093 gate didn’t embed properly .. so I have attached it this time. thankyou for your prompt reply. I understand the need for schmitt triggered inputs as you have pointed out. I guess for completeness I was also pointing out that the schematic should show the NAND gates with schmitt triggers as shown below.

2 input NAND with schmitt trigger 4093.

Reply from PB



Product Design - Industrial Automation and Instrumentation.

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