Nonvolatile status indicator switch

1. An aircraft electrical system comprising:

a fault detection circuit coupled to a relay; and

a fault indicator circuit coupled to the fault detection circuit and to a control input of the relay;

wherein the fault indicator circuit includes a nonvolatile memory element comprising a potentiometer having a nonvolatile memory;

wherein the fault detection circuit is configured to detect a fault and to provide a signal indicative of the fault to the fault indicator circuit; and

wherein the fault indicator circuit is configured to respond to the signal indicative of the fault by providing a predetermined control signal to the relay and by storing information indicative of the detection of the fault in the nonvolatile memory of the potentiometer.

2. The aircraft electrical system of claim 1 , wherein the fault indicator circuit is configured to receive a reset signal and to clear the nonvolatile memory element based on the reset signal.

3. The aircraft electrical system of claim 1 , wherein the fault indicator circuit is configured to:

receive an external control signal;

allow the external control signal to pass through the fault indicator circuit to the control input of the relay when the nonvolatile memory element does not contain information indicative of the detection of a fault; and

prevent the external control signal from passing to the control input of the relay when the nonvolatile memory element contains information indicative of the detection of a fault.

4. The aircraft electrical system of claim 1 , wherein the fault indicator circuit includes:

an input logic circuit configured to receive the signal indicative of a fault and to receive a signal indicative of a request to reset the nonvolatile memory element; and

a switch coupled to an output of the input logic circuit, the switch configured to prevent flow of the control signal to the relay when the nonvolatile memory element contains information indicative of the detection of a fault.

5. The aircraft electrical system of claim 4 , wherein the switch includes at least one transistor.

6. The aircraft electrical system of claim 4 , wherein the switch is an electromechanical switch.

7. The fault indicator circuit of claim 4 , wherein the input logic circuit is configured to generate a first output signal indicating the existence of a fault, where the first output signal is derived from the reset signal and the fault signal.

8. The fault indicator circuit of claim 4 , wherein the input logic circuit and the nonvolatile memory element are implemented in at least one of a programmable logic device and an ASIC.

9. The aircraft electrical system of claim 1 , wherein the fault indicator circuit further includes a visual indicator for providing a visual indication of a stored fault.

10. The aircraft electrical system of claim 9 , wherein the visual indicator includes at least one LED.

11. The aircraft electrical system of claim 9 , wherein the visual indicator is a pop-up button.

12. The aircraft electrical system of claim 11 ,

wherein the fault indicator circuit further includes a manual reset mechanism configured to receive a resetting stimulus and to generate the reset request signal responsive to the resetting stimulus; and

wherein the pop-up button provides the resetting stimulus when it is pushed down.

13. The aircraft electrical system of claim 1 , wherein the relay controls the flow of current from a power source to a load.

14. The fault indicator circuit of claim 1 , wherein the potentiometer is a digital potentiometer having at least one high resistance position and at least one low resistance position, wherein the fault indicator circuit is configured to store a fault as one of the at least one high resistance position and the at least one low resistance position.

15. The fault indicator circuit of claim 1 , wherein the nonvolatile memory element includes a one-bit memory element.

16. A method for controlling a relay in an airplane electrical system, the method comprising:

detecting at least one fault;

storing a record of the at least one fault using a potentiometer comprising a solid state nonvolatile memory;

maintaining the record of the at least one fault in the absence of power;

clearing the record of the at least one fault when a reset signal is received; and

opening a relay to stop a flow of current to a load in the airplane electrical system when the at least one fault is stored.

17. A fault indicator circuit comprising:

an input logic circuit configured to receive a fault signal indicative of a detection of a fault and a reset signal indicative of a request to reset the fault; and

an electromechanical switch coupled to an output of the input logic circuit, where the output of the input logic circuit is derived from the fault signal and the reset signal;

wherein the electromechanical switch is configured to control a relay in response to the output of the input logic circuit; and

wherein an exterior housing of the electromechanical switch is surrounded by a shielding material that reduces an impact of external magnetic fields on operation of the electromechanical switch.

18. The fault indicator circuit of claim 17 , wherein the electromechanical switch is a Reed switch.

19. The fault indicator circuit of claim 17 , wherein a shielding capability of the shielding material is greater than a magnetic sensitivity of the electromechanical switch.

20. The fault indicator circuit of claim 17 , wherein the shield is comprise of a magnetic ferrous material.