The last section was a design introduction of a data logging system and its operation. This section will cover the power requirement of that system starting with each of its components. Datasheets are the primary source for this information.
Having enough power to operate the system for the duration of flight is the essential goal. If power loss occurs midway in flight, there is a chance that all data will be lost. Here is list of the components and the power needed to run them.
ESP32-Cam: 5V 310mA (Flash lamp on 100%) – https://media.digikey.com/pdf/Data%20Sheets/DFRobot%20PDFs/DFR0602_Web.pdf
Current Sensor: 5V 7mA – https://cdn-shop.adafruit.com/datasheets/ina219.pdf
Barometer: 3.3V ~10mA – https://www.sparkfun.com/datasheets/Components/General/BST-BMP085-DS000-05.pdf
GPS: 3.3V 40mA – https://cdn.sparkfun.com/datasheets/GPS/GP-20U7.pdf
There are 2 voltage buses, 5 and 3.3 volts. Luckily, the ESP32-Cam module has an onboard 3.3 linear voltage regulator, https://www.ti.com/lit/ds/symlink/lm2937.pdf. The datasheet specs reveal that it can safely supply ~50mA to the 3.3V bus. So this narrows the supply requirement to be able to handle 5V ~375mA for the duration of the flight.
Supplying a steady 5 volts is a must. The system will not operate reliably with any variation above or below that value. Some kind of voltage regulation will need to be used. The ST LFXX linear regulator was selected because it could handle the 5V ~375mA load, https://www.st.com/content/ccc/resource/technical/document/datasheet/c4/0e/7e/2a/be/bc/4c/bd/CD00000546.pdf/files/CD00000546.pdf/jcr:content/translations/en.CD00000546.pdf. The datasheet also mentioned it was good for the job, “The low drop voltage (450 mV) and low quiescent current make it particularly suitable for low-noise, low-power applications and especially in battery powered systems.” It outclassed the switching voltage regulator. This is because the switching voltage regulator had additional cost, weight, and a higher chance of possible interference.
Next was selecting the battery to supply the power. It had to be at least 5.45V for the voltage regulator. Something higher would be better due to a voltage drop when the load was applied. Using a 6 volt battery still wasn’t practical. Using a standard 9V battery may seem good, but the weight and reuse were an issue. The battery selected was a 2S 7.4V lipo pack that was rated for 280mAH at 30C, https://www.horizonhobby.com/product/7.4v-280mah-2s-30c-lipo-battery-ph/EFLB2802S30.html. With 7.4 volts times 280mAH, the battery can handle 2 watts for 1 hour. The system estimates had it consuming ~1.875 watts, 5V times ~375mA. This left headroom, so it was within the limits for flight time.
Having the power source matched up with the devices clears way for the next development phase, firmware.