Yet another implementation of a Set-Reset flip-flip, this time using NAND gates.
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.
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub
Here’s a quick demo: