# Autonomous Active Tag Using Energy Harvesting Strategies
## 2 Materials and Methods
### Application and Scenarios
#### 2.4.2 Processing Module Scenarios  
There are different scenarios in processing module relating to the consumption of the module in order to discover whether the operations modes of our application are supported by the power module. The supercapacitor is the source of energy and it is where the current consumption is to be checked. The device turns off when the voltage in the supercapacitor is lower than 2.7 V. Power consumption was measured with a moving coil ammeter and a B2902A Precision Source/Measure Unit [19]. * Low power consumption scenario  
This is the main tag mode as it is the most usual scenario along the tag's lifetime. For that reason, we optimized consumption in this mode, so it has the lowest power consumption with respect to the others. There are periodic peaks in consumption when the transceiver changes from sleep mode to reception mode. The duty-cycle is 50% for a period of 1 s, which is higher than what our application needs, but is useful for evaluating the consumption of the reception and sleep modes. The microcontroller stays in the stop mode with RTC. EEPROM stays in standby mode because no read/write operation is used in this scenario. In this scenario, the EEPROM, the transceiver and the microcontroller are in low power consumption modes, as has been explained in the description of this test's setup. We use the name \"low power mode\" to refer to this configuration. The transceiver wakes up in reception mode during 0.5 s every 1 s, where the transition switches between reception mode and sleep mode. The expected consumption, according to their datasheets, are between 34.5 \(\upmu\)A and 41.5 \(\upmu\)A in sleep mode and 7 mA in the peaks of reception just for the transceiver. The consumption in stop mode is 0.8 \(\upmu\)A for the microcontroller. Since it is the mode in which the tag stays the longest, it is important to know how much time it can be on while the previously fully charged supercapacitor is discharging, and without any source of power. In order to do so, the current consumption has to be measured with the objective of optimizing it. * Transmission scenario In this scenario, the microcontroller reads data from the EEPROM and uses the transceiver to send them to a hypothetical reader. Tests are carried out for one datum and for all data available in the EEPROM. This test allows the transmission power consumption to be isolated. The microcontroller uses the active mode continuously, so we can measure the transmissions consumption. The transceiver switches to transmission mode (TX) when the microcontroller wants to send a package, which occurs every second in this scenario. The EEPROM switches to active mode when performing read operations and stays in standby mode the rest of the time. First, it sends one datum, which is formed by 2 bytes of payload, and then it sends a data package of maximum length, which is formed by 128 bytes of payload, at 38.4 Kbps. The theoretical current draw needed to complete the transmissions is of 11.5 mA for transmission mode (TX) in the transceiver, 3 mA for the use of the EEPROM and in the order of 0.87 milliamperes for the microcontroller. The data are transmitted periodically at a rate of 1 package per 1 s.  
* Reception scenario In this scenario, the data reach the transceiver and then pass to the microcontroller, which processes them to understand the purpose of the package. Following that, it uses the EEPROM to accomplish the specified task. Then, the microcontroller sends a response containing the requested data or a received acknowledgement (ACK). This is the configuration that best fits with our application case, because, a transmission is performed after every reception. The microcontroller the uses active mode all the time for processing the receptions and transmissions as it is the best way to measure the consumption of package reception. The transceiver switches between reception, sleep and transmission modes. The EEPROM also switches between standby and active modes.