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I need to design an edge detection circuit to detect when a square wave signal goes from Low to High (rising edge) and when it goes from High to Low (falling edge). The circuit should preferably use simple logic control such as 74LS series logic. I know people are gonna suggest using an arduino with interrupts but in my application this needs to be done in hardware rather than software.

Edit: The output is expected to be a short digital pulse, used as a trigger.

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  • \$\begingroup\$ A resistor, a capacitor, and an xor gate should do the trick. \$\endgroup\$
    – brhans
    Commented Jul 3, 2018 at 0:34
  • \$\begingroup\$ Did you ever bother to google for {edge detection with logic} ? Or Stack Exchange at least? electronics.stackexchange.com/q/270894/117785 I know it is not nice, but really? \$\endgroup\$
    – Ale..chenski
    Commented Jul 3, 2018 at 0:35
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    \$\begingroup\$ @AliChen, no, it is actually a second attempt to ask the same question electronics.stackexchange.com/questions/382104 \$\endgroup\$
    – Maple
    Commented Jul 3, 2018 at 1:07
  • \$\begingroup\$ @Maple, this is the second attempt by OP, true. But exactly this question was asked years ago and has perfect answers. \$\endgroup\$
    – Ale..chenski
    Commented Jul 3, 2018 at 4:10

2 Answers 2

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How about this

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ the circuit looks good, but also explain the working. like if the input contains a clock how does the output change as the clock rises, stays positive and then falls. \$\endgroup\$
    – Prashant Pugalia
    Commented Dec 4, 2022 at 12:14
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A simple differentiator circuit should do what you ask(the pulse will be fairly short but enough to trigger a bistable multivibrator or something). Read more at https://www.electronics-tutorials.ws/opamp/opamp_7.html: enter image description here

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    \$\begingroup\$ Your circuit produces negative spike on falling edge. I suspect it is not what OP wants even though he refuses to tell what he's connecting edge detecting circuit to. \$\endgroup\$
    – Maple
    Commented Jul 3, 2018 at 1:15
  • \$\begingroup\$ Wouldn't the negative spike be on the rising edge? \$\endgroup\$
    – atomSmasher
    Commented Jul 3, 2018 at 3:14
  • \$\begingroup\$ He can add a diode if he doesn't want the negative edge. \$\endgroup\$
    – user1949350
    Commented Jul 3, 2018 at 7:39

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