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need help on nand gates connection

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naren

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hi,

would like to know if nand gates output could be connected as mentioned in the circuit or do i need to add an diode(pls advice on part number)?

This output is connected such as, due to 2 things could control the circuit (e.g a manual switch and a computer using 4N25).

pls advice

naren
 

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Yes, diodes or "OR" gate is required at the output of two NAND gates.
 
1N4001 would work, though I would have recommended something a little smaller, eg, 1N4148 or 1N914
 
diodes

Or, you could do this, since a NAND gate is equivalent to a negative-logic OR (limits you to 2 inputs, though).

For a good overview of designing a schmitt-trigger debounce circuit:

**broken link removed**
 

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more inputs

Here's an afterthought. You could wire the NAND gates as shown to get up to four different inputs with one IC (74HC132 or CD4093). Each input has it's own switch and RC, as before. Tie any unused inputs high.
 

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