System for measuring the power level of an ambient energy source
The invention concerns a measurement unit including: an electric ambient energy recovery generator; an element of capacitive storage of the electric energy generated by the generator; an electric battery; a first branch coupling an output node of the generator to a first electrode of the capacitive storage element; a second branch coupling a first terminal of the battery to the first electrode of the capacitive storage element; and an active circuit capable of transmitting a radio event indicator signal each time the voltage across the capacitive storage element exceeds a first threshold, wherein, in operation, the capacitive storage element simultaneously receives a first charge current originating from the generator via the first branch and a second charge current originating from the battery via the second branch.
1. A measurement unit comprising:
an electric ambient energy recovery generator;
an element of capacitive storage of the electric energy generated by the generator;
an electric battery;
a first branch coupling an output node of the generator to a first electrode of the capacitive storage element;
a second branch coupling a first terminal of the battery to the first electrode of the capacitive storage element; and
an active circuit capable of transmitting a radio event indicator signal each time the voltage across the capacitive storage element exceeds a first threshold,
wherein, in operation, the capacitive storage element simultaneously receives, on its first electrode, a first charge current originating from the generator via the first branch, and a second charge current originating from the battery via the second branch.
2. The unit of claim 1 , wherein the first branch comprises a first resistor and the second branch comprises a second resistor.
3. The unit of claim 1 , wherein the second branch comprises a circuit for protecting the battery against an over-discharge.
4. The unit of claim 3 , wherein the circuit for protecting the battery against an over-discharge comprises a transistor coupling the first terminal of the battery to the first electrode of the capacitive storage element, and a circuit capable of controlling this transistor to the on state when the voltage across the battery is higher than a low limit below which the battery would risk being damaged, and to the off state when the voltage across the battery is lower than said low limit.
5. The unit of claim 1 , wherein the first branch comprises a diode oriented in the forward direction between the output node of the generator and the first electrode of the capacitive storage element.
6. The unit of claim 1 , wherein the second branch comprises a diode oriented in the forward direction between the first terminal of the battery and the first electrode of the capacitive storage element.
7. The unit of claim 1 , further comprising a third branch coupling the output node of the generator to the first terminal of the battery.
8. The unit of claim 7 , wherein the third branch comprises a circuit for protecting the battery against an overcharge.
9. The unit of claim 8 , wherein the circuit for protecting the battery against an overcharge comprises a transistor coupling the output node of the generator to the first terminal of the battery and a circuit capable of controlling this transistor to the on state when the voltage across the battery is lower than an upper limit above which the battery would risk being damaged, and to the off state when the voltage across the battery is higher than said upper limit.
10. The unit of claim 7 , wherein the third branch further comprises a circuit for limiting the charge current applied to the battery.
11. The unit of claim 10 , wherein the current-limiting circuit comprises a transistor and a circuit capable of controlling this transistor in linear state so that the resistance of the transistor is all the higher as the current applied by the generator in the third branch is high.
12. The unit of claim 7 , wherein the third branch further comprises a diode oriented in the forward direction between the output node of the generator and the first terminal of the battery.
13. The unit of claim 1 , wherein the active circuit has a power supply node coupled to the first electrode of the capacitive storage element via a switch, and wherein the unit comprises a control circuit capable of controlling the switch to the on state when the voltage across the capacitive element exceeds said first threshold.
14. The unit of claim 13 , wherein the control circuit is further capable of controlling the switch back to the off state when the voltage across the capacitive element falls below a second threshold lower than the first threshold.
15. A system comprising one or a plurality of measurement units of claim 1 , and a data collection unit capable of receiving the event indicator signals transmitted by each unit, and of measuring a time quantity representative of the frequency of transmission of the event indicator signals by each unit.