Wireless sensor including an RF signal circuit
A wireless sensor includes an antenna structure, an RF signal circuit, a sensing element, memory and a processing module. In a calibration mode, the sensing element is exposed to a known condition and causes a first change of an operating characteristic of the antenna structure while receiving the RF signal. The processing module generates a first digital value based on the first change and writes it into the memory. In a sense mode, the sensing element is exposed to an unknown condition and causes a second change of an operating characteristic of the antenna structure while receiving the RF signal. The processing module generates a second digital value based on the second change and writes it into the memory.
1. A wireless sensor comprises:
an RF signal circuit operable to, when enabled, produce a radio frequency (RF) signal;
an antenna structure operable to receive the RF signal;
a sensing element operably coupled to the antenna structure, wherein, in a calibration mode, the sensing element is exposed to a known condition and causes a first change of an operating characteristic of the antenna structure while receiving the RF signal and wherein, in a sense mode, the sensing element is exposed to an unknown condition and causes a second change of the operating characteristic of the antenna structure while receiving the RF signal;
memory; and
a processing module operable to:
in the calibration mode:
generate a first digital value based on the first change of the operating characteristic, wherein the first digital value is representative of the known condition; and
write the first digital value into the memory; and
in the sense mode:
generate a second digital value based on the second change of the operating characteristic, wherein the second digital value is representative of the second change corresponding to the unknown condition; and
write the second digital value into the memory.
2. The wireless sensor of claim 1 further comprises:
a power circuit operable to generate a power supply voltage, wherein the power circuit is coupled to the processing module, the RF signal circuit, and the memory.
3. The wireless sensor of claim 2 , wherein the power circuit comprises one of:
an active power supply circuit; and
a passive power supply circuit that includes a power harvesting circuit and a power sourcing circuit.
4. The wireless sensor of claim 1 , wherein the RF signal circuit comprises:
an oscillator to generate an oscillation; and
an antenna operably coupled to transmit the oscillation as the RF signal.
5. The wireless sensor of claim 1 , wherein the sensing element is operable to sense a condition that comprises one or more of:
a moisture level;
pressure;
temperature;
a gas level; and
proximity.
6. The wireless sensor of claim 1 further comprises:
a real time clock, wherein the processing module is further operable to:
time stamp the first digital value; and
time stamp the second digital value.
7. The wireless sensor of claim 1 further comprises:
a real time clock, wherein the processing module is further operable to, in the sense mode:
enable the RF signal circuit at periodic intervals;
for each periodic interval:
generate a digital value representing a change of the operating characteristic of the antenna structure while receiving the RF signal caused by the sensing element being exposed to varying conditions to produce a plurality of digital values;
time stamp each digital value of the plurality of digital values to create a plurality of time stamps; and
write the plurality of digital values and the plurality of time stamps into the memory.
8. The wireless sensor of claim 1 further comprises:
a transmitter, wherein:
the antenna structure is operable to receive a second RF signal from a sensor computing device;
the processing module is operable to:
extract a message from the second RF signal;
retrieve at least one of the first and second digital values from the memory in response to the message; and
provide the at least one of the first and second digital values to the transmitter for RF transmission to the sensor computing device.
9. The wireless sensor of claim 1 , wherein the processing module is further operable to generate the first digital value based on the first change of the operating characteristic by:
adjusting a tuning circuit operably coupled to the antenna structure to further change the operating characteristic of the antenna structure such that the antenna structure is in substantial resonance with the RF signal;
interpreting an amount of the further change; and
generating the first digital value based on the amount of the further change.
10. The wireless sensor of claim 1 , wherein the processing module is further operable to generate the second digital value based on the second change of the operating characteristic by:
adjusting a tuning circuit operably coupled to the antenna structure to further change the operating characteristic of the antenna structure such that the antenna structure is in substantial resonance with the RF signal;
interpreting an amount of the further change; and
generating the second digital value based on the amount of the further change.
11. An active wireless sensor comprises:
a battery;
a power circuit operably coupled to generate a power supply voltage from the battery;
an RF signal circuit operable to, when enabled, produce a radio frequency (RF) signal;
an antenna structure operable to receive the RF signal;
a sensing element operably coupled to the antenna structure, wherein, when the sensing element is exposed to a condition, the sensing element causes a change of an operating characteristic of the antenna structure while receiving the RF signal;
memory operably coupled to the power supply circuit; and
a processing module operably coupled to the power supply circuit and to the memory, wherein the processing module is operable to:
generate a digital value based on the change of the operating characteristic, wherein the digital value is representative of the condition; and
write the digital value into the memory.
12. The active wireless sensor of claim 11 , wherein the RF signal circuit comprises:
an oscillator to generate an oscillation; and
an antenna operably coupled to transmit the oscillation as the RF signal.
13. The active wireless sensor of claim 11 , wherein the sensing element is operable to sense a condition that comprises one or more of:
a moisture level;
pressure;
temperature;
a gas level; and
proximity.
14. The active wireless sensor of claim 11 further comprises:
a real time clock, wherein the processing module is further operable to time stamp the digital value.
15. The active wireless sensor of claim 11 further comprises:
a real time clock, wherein the processing module is further operable to:
enable the RF signal circuit at periodic intervals;
for each periodic interval:
generate the digital value representing the change of the operating characteristic of the antenna structure while receiving the RF signal caused by the sensing element being exposed to varying conditions to produce a plurality of digital values;
time stamp each digital value of the plurality of digital values to create a plurality of time stamps; and
write the plurality of digital values and the plurality of time stamps into the memory.
16. The active wireless sensor of claim 11 further comprises:
a transmitter, wherein:
the antenna structure is operable to receive a second RF signal from a sensor computing device;
the processing module is operable to:
extract a message from the second RF signal;
retrieve the digital value from the memory in response to the message; and
provide the digital value to the transmitter for RF transmission to the sensor computing device.
17. The active wireless sensor of claim 11 , wherein the processing module is further operable to generate the digital value based on the change of the operating characteristic by:
adjusting a tuning circuit operably coupled to the antenna structure to further change the operating characteristic of the antenna structure such that the antenna structure is in substantial resonance with the RF signal;
interpreting an amount of the further change; and
generating the digital value based on the amount of the further change.