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I will use a motor adapter in my design.This motor adapter doesn't have a spice model. Therofore I will design inside structure of this adapter. In this motor adapter has a delay and xor gate part.I think this part makes edge detection.By using below reference desing from this website rising edge (0 to1)and falling edge(1 to 0) detector circuit for flipflops? I built a edge detector circuit in LTSpice by using 74HCT04 inverters. But 74HCT04 gives only inverse of input, it doesn't give any delay. How 74hct04 can give delay and how I can obtain an positive edge detector by using delay and xor gate?

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engineergc
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2 Answers2

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Here's the general idea about edge detectors: -

enter image description here

Three examples all of which use an RC to slightly delay one input to the gate (schmitt input type gate of course).

But 74HCT04 gives only inverse of input, it doesn't give any delay.

Oh yes it does, read the data sheet (it tells you that the propagation delay is about 7 ns on a 5V supply) and, if you want more delay add more inverters: -

enter image description here

Or this: -

enter image description here

If you just want a positive edge detector use the 2nd circuit in your question with an odd number of gates.

Andy aka
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  • Thank you, I understand structure of edge detectors . But I can not understand function of or gate, nor gate and sr latch. At the Q output of SR latch I take 5 volt. I think this 5V provide transistor(connected to Q output) to stay conduction continuously , but I am not sure. – engineergc Nov 18 '16 at 12:54
  • I have answered your question so, whats all this about. What precisely don't you understand ? – Andy aka Nov 18 '16 at 13:02
  • My main purpose in design internal structure of motor adapter that I added picture above. In motor adapter I can not understand function of or gate, nor gate and sr latch. Why these are used? – engineergc Nov 18 '16 at 13:19
  • @engineergc your question was "How 74hct04 can give delay and how I can obtain an positive edge detector by using delay and xor gate?" and to provide you with a detailed breakdown of how OR, NOR and an SR latch works is really beyond the scope of this site so, have you done any investigation using google about logic devices and, if not, why not and, if so where and what don't you understand? – Andy aka Nov 18 '16 at 14:13
  • There are whole books written on logic gates and for me to try and precy an answer here without knowing what you don't understand is absolutely pointless - that is whay I ask you to state a specific area you don't understand. If you can't be specific I'm not going to waste my time trying to guess what you don't know and, once again, I point to your question and ask you why you didn't mention this in the first place. We give free advice but there comes a point where any of us will back away from a person moving the goalposts. – Andy aka Nov 18 '16 at 14:15
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This is from an LT spice manual I searched for on line;

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You should set the TD paramater on your 7404 device to something other than 0.

owg60
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