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I need a VERY simple latching circuit using comparator that will simply be off until a signal hits it (can be either + or -, I have no preference) and the circuit will remain on until I reset it.

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  • \$\begingroup\$ Think flip-flop :) \$\endgroup\$ – Peter Smith Dec 1 '15 at 19:20
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    \$\begingroup\$ bi-stable relais, thyristor \$\endgroup\$ – Wouter van Ooijen Dec 1 '15 at 19:24
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You could do something like this- the comparator output goes low when the input passes +2.50VDC (the voltage set by the R3/R3 resistor divider, which turns on the LED D1 and also Q1. Q1 pulls the inverting input up to +5 regardless of the voltage at the input so the LED will not turn off. SW1 shorts out the transistor drive so the LED will turn off and, if the input voltage is less than 2.5V, will stay off when the switch is released. Otherwise it will come on again immediately when the switch is released.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ pefhanny: Thank you.I build this circuit and it works fine. \$\endgroup\$ – Newbie Dec 8 '15 at 10:21
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With a comparator and a D-flipflop (74hc74) use the output of the comparator (with a pull-up resitor) as flipflop CLK. Set the flipflop D=1, S=1, and use R as reset. The output of the flipflop Q is the Latched output.

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  • \$\begingroup\$ You can use only a comparator and thristor at output, then when power off (or disconnect thyristor only) it will reset. \$\endgroup\$ – Marko Buršič Dec 1 '15 at 19:39
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schematic

simulate this circuit – Schematic created using CircuitLab

My first schematics, just as example

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  • \$\begingroup\$ where's a switch (or other means) to reset it? \$\endgroup\$ – tcrosley Dec 2 '15 at 2:55
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with a bit of positive feedback it's easy to make a comparitor latch.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ where's a switch (or other means) to reset it? \$\endgroup\$ – tcrosley Dec 2 '15 at 2:55
  • \$\begingroup\$ reset by pulling + input to VCC edit \$\endgroup\$ – Jasen Dec 2 '15 at 3:37

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