Set-Reset latch implemented with NAND gates.
Here's a quick demo of it in action..
This circuit is another implementation of a Set-Reset flip-flip, this time using NAND gates. A 74LS00 is used to provide the two NAND gates required.
The NAND gate implementatation has an undefined state with both inputs high, whereas a NOR gate implementatation has an undefined state with both inputs low.
Consequently NOR gates are typically used for active-high SR latches and NAND gates for active-low SR latches. A good example of this is the application in touch sensors, where active low makes sense. See the Boldport Club tap and mostap projects for examples of this.
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Here's a quick breadboard build using a 74LS00 quad two-input NAND gate, with some switches and LEDs to indicate S, R, Q and `Q: