Power Draw Preliminary:
Pressure sensor
Cleanup electronics
Number-making chip
Small computer
Saving data
Sending data
Power converters (waste some energy)
Does not use power:
Thermocouple metal wires
| Component | Amount | Power Draw | Worst Case | What is it?/Function |
|---|---|---|---|---|
| MAX31856 thermocouple-to-digital converter | 10 | 1.2mA during active conversion 5.25µA in standby | All active: 12 mA | Performs cold-junction compensation and linearization to provide highly accurate temperature; Supports Type-T |
| TE Connectivity MS4525DO digital pressure sensor | 1 | ~3 mA | PCB mount pressure transducer. Measures pressure and outputs a digital number. It can measure absolute pressure, gauge pressure, differential pressure, vacuum pressure and compound pressure from 1 to 150 psi. | |
| Microcontroller (STM32U5-class) | 1 | 5–20 mA (active, light code) | Reads sensors, timestamps, formats packets, manages logging + comms. Best “default choice” for low-power embedded payload control. | |
| GPIO expander | 1 | ~0.2–1 mA | Lets one MCU control 10 MAX31856 boards without running out of pins. | |
| microSD card | 1 | 20–80 mA while writing but might have peaks around 100mA | Saves data locally | |
| Oscillator / crystal | 1 | it's power is included in MCU | Provides the precise frequency needed for accurate timekeeping, acting as the heart of clocks and Real-Time Clocks (RTCs) that generate timestamps. While a crystal itself vibrates, an oscillator circuit uses it to create a stable clock signal | |
| ADDITIONAL | MAY | CORRESPOND | TO | COMMS |
| RS-422 transceiver | A way of sending 1s and 0s over two wires using electrical differences. Will send our microcontroller output to an RS-422 receiver in Oligo's OBC | |||
Total: (Not accounting RS-422 and worst case active sensing, converting to digital, storing and sending) | 116 mA, ~0.38 W | |||
| Total: (Not accounting RS-422 and worst case active sensing, converting to digital, storing and sending] | 336 mA, ~1.11 W | |||
| Total: (Sleeping mode, not actively measuring, MCU sleeping) | 0.013 W (from pressure sensor) |
Now, taking into account sampling of the thermocouples every 5 seconds:
Supply rail: 3.3 V
Sampling period: 5 s (0.2 Hz)
Awake time per sample: 0.1 s
Duty cycle: 2% awake / 98% sleep
Peak power (SD burst): ~1.1 W
| Active sensing + conversion + SD write (typical) | 116 mA | 0.38 W | |
| Worst-case peak (SD write burst) | 336 mA | 1.11 W |
Average power @ 0.2 Hz: ~0.02 W (20 mW)
| Awake (measuring + logging) | 0.38 W | 2% | 0.0076 W |
|---|---|---|---|
| Sleep (idle electronics) | 0.013 W | 98% | 0.0127 W |
Overall: ~1.1 W for peak capacity