Firmware System Monitoring

v6.0 adds three always-on system monitors to the firmware: battery voltage, board temperature and an RSSI history buffer. All of them are read inside the main loops (BEACON, SEARCH, LISTEN) so their values are always fresh on the OLED and over serial.

Battery monitor

Hardware

A 2:1 resistor divider samples the pack:

Connection	Value
BAT+ (TP4056 BAT+ rail)	100 kohm to GPIO 36
GPIO 36 (ADC1_CH0)	100 kohm to GND

At 4.2 V full charge the pin sees 2.1 V, safely inside the 3.3 V ADC range. GPIO 36 is ADC1, so it keeps measuring even while WiFi (ADC2) is active in CONFIG mode. It also frees GPIO 34 for the SW_DN button, which previously shared the pin with the divider.

Software

Constant	Value	Meaning
BATTERY_READ_MS	5000	Read interval in ms
BATTERY_FULL_MV	4200	Full-charge voltage
BATTERY_EMPTY_MV	3300	Empty cutoff
BATTERY_LOW_MV	3550	Low-battery warning threshold

• readBatteryMv(): analogReadMilliVolts() on GPIO 36, doubled for the divider, clamped to 0-4200 mV, cached for BATTERY_READ_MS.
• battPct(): linear map of 3300-4200 mV to 0-100%.
• Low-battery event: red LED blinks 4x, AEGIS:BATT:low;mv=.. is printed once, and the OLED glyph flashes at 400 ms; the warning resets when voltage recovers above the threshold.
• BATT serial command replies AEGIS:BATT:mv=..;pct=...

Calibration

If the reported voltage differs from a multimeter, adjust the divider factor in readBatteryMv() (multiply by 2.0-2.2 depending on resistor tolerance). See Battery Monitor Calibration for the full procedure and Cell Discharge Curve for the optional piecewise state-of-charge curve.

Board temperature

boardTempC() reads the ESP32 internal silicon sensor through temperatureRead() (Arduino-ESP32). Values in the 1-125 °C range are trusted; anything outside reports as 0.0 (sensor unavailable). It appears in:

• the AEGIS:STATE line from the STATUS command (temp=42.1);
• the serial STATUS debug block.

The internal sensor tracks the silicon, not the ambient air: use it as a trend indicator for thermal protection, not as a weather reading.

RSSI history buffer

recordRssi() pushes every RSSI sample (SEARCH and LISTEN loops) into a 120-sample ring buffer (RSSI_HIST_LEN). The OLED engine renders the buffer newest-to-oldest:

• SEARCH: the buffer replaces the plain fill bar with an oscilloscope-style trace inside the RSSI frame; the threshold tick and the sweeping caret remain.
• LISTEN: a dedicated trace frame with the threshold tick and the live RSSI/THR readout.

Unused slots read 0 and are skipped, so the trace fills from the right as samples accumulate. The buffer is RAM-only: it resets on deep sleep, exactly like the scan history.

Serial additions summary

Command / line	Reply
BATT	AEGIS:BATT:mv=3710;pct=52
Low battery (event)	AEGIS:BATT:low;mv=3510
STATUS	AEGIS:STATE:...;batt=3710;temp=42.1;up=312
HELP	includes BATT and MODE ... LISTEN