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An emergency stop with latching operation.
Safety regs demand that after an ESTOP is used, the machine requires an operator action to restart the machine. Resetting the ESTOP switch should not allow the machine to restart.
A Set-Reset flip-flop is used to maintain the latched state. When the NC ESTOP is activated (lower left switch), the stopped state is latched. The stopped state is reset only when the ESTOP is returned to inactive, followed by an OFF-ON toggle on the Fault Reset switch (upper left).
An AND gate with input delay is used to create a pulse on rising edge only, so that a positive action by the operator is always required to reset the ESTOP. (A push switch would be better!)
There is a small bug in the simulation, the flip-flop can start in an intermediate state at power on. In reality this would not happen, but one state would be picked randomly. To avoid this, a bootstrap circuit should be used to enter the Off state at startup.
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