SC-F001 Firmware

Solar-powered automated crop harvesting robot built on the ESP32. Drives a carriage horizontally via a drive motor, lifts/lowers a cutting head via a jack motor, with an auxiliary "fluffer" motor always running during operation. The firmware handles motor sequencing, safety interlocks, remote control, data logging, and a WiFi web interface.

Primary operational cycle: Idle → Move Start Delay → Jack Up → Drive → Jack Down → Idle

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Hardware Platform

MCU: ESP32 (Xtensa dual-core), ESP-IDF framework

GPIO Map:

GPIO	Function
13	Button interrupt (active low, pull-up) — also EXT0 wakeup
14	Jack position sensor / encoder
16	Drive encoder
19	Aux sensor 2 (reserved)
21/22	I2C SDA/SCL (400kHz) → TCA9555 I/O expander
25	433MHz RF receiver (RMT input)
26	Solar charger bulk enable (RTC GPIO, holds across deep sleep)
27	Safety sensor (active low)
32/33	External 32.768 kHz RTC crystal (standard watch crystal, 2¹⁵ Hz)
36 (VP)	ADC: drive current sense
39 (VN)	ADC: battery voltage
34	ADC: jack current sense
35	ADC: aux current sense

TCA9555 (I2C at 0x20):

• Port 0 (input): 2 physical buttons + 2 additional inputs
• Port 1 (output): 3× H-bridge relay pairs (DRIVE, JACK, AUX) + LEDs

Motor / Bridge Specs:

• BRIDGE_DRIVE — 100A max, ACS37220 sense chip (13.2 mV/A, inverted polarity)
• BRIDGE_JACK — 30A max, ACS37042 sense chip (44 mV/A)
• BRIDGE_AUX — 30A max, ACS37042 sense chip (44 mV/A)

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Software Architecture

app_main()
├── rtc_xtal_init()         RTC crystal + EXT0 wakeup + sleep wakeup check
├── i2c_init()              TCA9555 init (relays off, LEDs off)
├── adc_init()              ADC1 calibration (12dB attenuation, line-fit)
├── storage_init()          Flash params + circular log buffer
├── solar_run_fsm()         (called in main loop too)
├── uart_init()             Serial JSON API task
├── rf_433_init()           433MHz RMT receiver task
├── bt_hid_init()           BLE HID host scanner task
├── fsm_init()              Control FSM task (priority 10, 20ms tick)
└── webserver_init()        WiFi softAP + HTTP + mDNS + DNS

Main loop (50ms):
    i2c_poll_buttons()
    fsm_request() based on button events
    solar_run_fsm()
    driveLEDs() status animation
    rtc_check_shutdown_timer() → deep sleep on inactivity (180s)

FreeRTOS Tasks:

Task	Created by	Priority	Tick	Purpose
app_main (main loop)	system	1 (default)	50ms	Button polling, LED animation, solar FSM, shutdown timer
control_task	fsm_init()	10	20ms	FSM state machine, relay control, ADC current monitoring, e-fuse
UART task	uart_init()	default	event-driven	Serial JSON command processing
RF 433 task	rf_433_init()	default	event-driven	RMT receive + keycode matching
BT HID task	bt_hid_init()	default	event-driven	BLE HID host scanning + button mapping
httpd workers	webserver_init()	default	event-driven	HTTP request handling (multiple workers spawned by esp_http_server)

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Key Files

File	Purpose
main.c	Entry point, 50ms main loop, factory reset, LED animation
control_fsm.c/h	State machine, relay control, current monitoring, calibration
power_mgmt.c/h	ADC reading, e-fuse thermal algorithm, battery voltage
sensors.c/h	GPIO ISR-based sensor debouncing, encoder counters
i2c.c/h	TCA9555 relay/LED/button control
storage.c/h	47-param NVM table + circular binary log buffer
comms.c/h	Unified GET/POST JSON API (shared by HTTP and UART)
webserver.c/h	WiFi softAP, HTTP server, embedded gzip webpage
uart_comms.c/h	Serial JSON interface (115200 8N1)
rf_433.c/h	433MHz OOK receiver, keycode learn/match
bt_hid.c/h	BLE HID host, media remote button mapping
rtc.c/h	Unix time, harvest alarms, deep sleep scheduling
solar.c/h	Simple FLOAT/BULK solar charge state machine
sc_err.h	Error code definitions
log_test.c/h	Flash log unit tests
hard_ui.c	Legacy LCD code (unused/obsolete)

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Control FSM States

STATE_IDLE
STATE_MOVE_START_DELAY      (1s)
STATE_JACK_UP_START         (detect current spike → jack engaged)
STATE_JACK_UP               (continue until timer/e-fuse)
STATE_DRIVE_START_DELAY     (1s)
STATE_DRIVE                 (encoder-based distance control)
STATE_DRIVE_END_DELAY       (1s)
STATE_JACK_DOWN             (reverse until e-fuse/sensor)
→ back to STATE_IDLE

STATE_UNDO_JACK_START       (emergency: reverse jack immediately)
STATE_UNDO_JACK             (run until e-fuse/sensor)
→ back to STATE_IDLE

CAL_JACK_DELAY / CAL_JACK_MOVE          (jack calibration sequence)
CAL_DRIVE_DELAY / CAL_DRIVE_MOVE        (drive calibration sequence)

Guards before START:

• Remaining distance > 0 (leash protection)
• Battery V ≥ LOW_PROTECTION_V (default 10V)
• Safety sensor active (debounced stable)
• All e-fuses not tripped

FSM Loop (20ms tick in control_task()):

1. process_bridge_current() — ADC → EMA → auto-zero → e-fuse
2. process_battery_voltage() — ADC → EMA
3. sensors_check() — drain ISR queue, update counters/debounce
4. State machine transitions (timer + sensor + efuse checks)
5. driveRelays() — write relay output from current state
6. send_fsm_log() — 39-byte timestamped entry to flash

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E-Fuse Algorithm (power_mgmt.c)

Per bridge, each 20ms tick:

1. Raw ADC → EMA filter (α = ADC_ALPHA_ISENS)
2. Auto-zero: learn zero offset when motor is off + grace period expired
3. Grace period: 250ms after relay closes (ignores startup inrush)
4. Instant trip: I ≥ EFUSE_KINST × I_nom (default 2×)
5. Thermal trip: heat accumulates as I²·Δt; dissipates at τ_cool rate
6. Auto-reset: after EFUSE_TCOOL seconds of cooling (default 5s)

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Safety Sensor Debouncing (Asymmetric)

LOW (safe):   1000ms make time  → slow to declare safe (SAFETY_MAKE_US)
HIGH (break): 300ms break time  → fast to kill operation (SAFETY_BREAK_US)

Safety break → immediate STATE_UNDO_JACK_START.

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Communication Interfaces

WiFi (softAP)

• SSID/password/channel configurable via params (WIFI_SSID, WIFI_PASS, WIFI_CHANNEL)
• mDNS hostname: sc.local
• Captive portal DNS: all queries → 192.168.4.1
• HTTP port 80

HTTP API (port 80)

Endpoint	Method	Description
/	GET	Embedded gzip HTML webpage
/get	GET	JSON system status
/set	POST	JSON commands + parameter updates
/log	GET	Binary log download (4B JSON len + JSON + 8B offsets + log data)

UART (115200 8N1)

• GET → same as HTTP GET /get
• POST: {json} → same as HTTP POST /set
• HELP → command reference
• Shares comms_handle_get() / comms_handle_post() with HTTP

433MHz RF (GPIO25, RMT)

• 24-bit OOK codes (P_HIGH≈1040µs, P_LOW≈340µs, margin 70µs)
• 8 stored keycodes → FSM_OVERRIDE_* commands
• Learn mode: capture next RX → temp buffer → user commits via web

Bluetooth HID Host

• Scans for BLE HID devices (service UUID 0x1812)
• Tries saved BDA first, then scans for best RSSI
• Button mapping:
  • VOL_UP → Jack Up (override pulse)
  • VOL_DOWN → Jack Down
  • PREV → Drive Reverse
  • NEXT → Drive Forward

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Storage Layout

Flash partition "storage":

0x0000 – 0x0FFF   Parameters (4 sectors, CRC32-protected, 47 params)
0x1000 – end      Circular log buffer (head/tail tracked)

Log entry format (39 bytes typical):

[0:8]   Timestamp ms (u64 BE)
[8:12]  Battery voltage (f32)
[12:16] Drive current (f32)
[16:20] Jack current (f32)
[20:24] Aux current (f32)
[24:26] Drive encoder count (i16)
[26]    Sensor states (packed)
[27:31] Drive heat (f32)
[31:35] Jack heat (f32)
[35:39] Aux heat (f32)

Key Parameters:

• Motion: DRIVE_DIST, JACK_DIST, DRIVE_KT, JACK_KT, DRIVE_KE
• E-fuse: EFUSE_INOM_1/2/3, EFUSE_HEAT_THRESH, EFUSE_KINST, EFUSE_TCOOL
• Safety: SAFETY_BREAK_US, SAFETY_MAKE_US, LOW_PROTECTION_V
• RF: KEYCODE_0 … KEYCODE_7
• WiFi: WIFI_SSID, WIFI_PASS, WIFI_CHANNEL
• Schedule: NUM_MOVES, MOVE_START, MOVE_END (seconds-since-midnight)

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RTC & 32.768 kHz Crystal

Crystal: Standard 32.768 kHz (32768 Hz = 2¹⁵ Hz) tuning-fork watch crystal on GPIO32/GPIO33. This frequency is universal for RTCs because it divides to exactly 1 Hz with a 15-bit binary counter.

sdkconfig.defaults settings:

• CONFIG_RTC_CLK_SRC_EXT_CRYS=y — selects the external crystal as the RTC slow clock source instead of the internal ~150 kHz RC oscillator
• CONFIG_ESP32_RTC_EXT_CRYST_ADDIT_CURRENT_V2=y — enables extra drive current during the crystal startup window; required for high-ESR tuning-fork crystals (e.g. CM315D32768DZFT ~70 kΩ ESR)

Known startup failure mode: On power-on, the ESP32 bootloader attempts to calibrate the crystal. If it fails to detect oscillation within its calibration window, it logs W: 32 kHz XTAL not found, switching to internal 150 kHz oscillator and falls back to the RC oscillator. The RC oscillator has ±5% accuracy, producing up to ~180 s/hr of RTC drift — this completely breaks harvest scheduling.

Firmware mitigation (rtc_xtal_init() in rtc.c): If rtc_clk_slow_src_get() does not return SOC_RTC_SLOW_CLK_SRC_XTAL32K at startup, the code applies a manual bootstrap: rtc_clk_32k_bootstrap(20000) (~600 ms of extra drive current at 32 kHz cycles), waits 500 ms for oscillation to stabilise, then calls rtc_clk_slow_src_set(SOC_RTC_SLOW_CLK_SRC_XTAL32K) to switch explicitly. Success or failure is logged via ESP_LOGI/LOGE.

Diagnosing crystal issues: Run RTCDEBUG over UART and check slow_clk_src. It reports either XTAL32K (OK) or NOT XTAL32K — check crystal!. The logtool/rtc_test.py script automates this and runs multi-cycle drift tests.

Time persistence across deep sleep: rtc_backup_s and rtc_sleep_entry_s are RTC_DATA_ATTR (survive deep sleep). On wakeup, rtc_restore_time() adds exactly DEEP_SLEEP_US / 1e6 seconds to rtc_sleep_entry_s to reconstruct the correct time without an NTP sync.

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Power Management

• Battery voltage: GPIO39, divider → V = raw × 0.00767 + 0.4
• Solar charger: GPIO26 (RTC hold) — FLOAT/BULK FSM, bulk for 20s when V < 5V for 5s
• Inactivity shutdown: 180s → deep sleep
• Deep sleep wakeup: RTC timer (120s), RTC alarm (next harvest), EXT0 GPIO13 (button)
• RTC_DATA_ATTR: FSM state, errors, alarm times, charge state — survive deep sleep

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Error Codes (sc_err.h)

SC_ERR_EFUSE_TRIP_1  = 0x201  // Drive overcurrent/overheat
SC_ERR_EFUSE_TRIP_2  = 0x202  // Jack
SC_ERR_EFUSE_TRIP_3  = 0x203  // Aux
SC_ERR_SAFETY_TRIP   = 0x210  // Safety sensor break
SC_ERR_LEASH_HIT     = 0x211  // Distance limit reached
SC_ERR_RTC_NOT_SET   = 0x220  // Clock not synchronized
SC_ERR_LOW_BATTERY   = 0x230  // Voltage below threshold

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Build System

• Framework: ESP-IDF (>=4.1.0)
• Component deps (idf_component.yml): espressif/mdns, joltwallet/littlefs, esp-idf-lib/tca95x5
• IDF requires: driver, esp_http_server, esp_netif, lwip, json, esp_timer, esp_adc, app_update, esp_wifi, nvs_flash, mdns, bt, esp_hid
• Webpage: webpage.html → webpage_compile.py → webpage_gzip.h (embedded gzip binary). Must re-run webpage_compile.py after any HTML edit before building.
• Version: version.h.in filled by CMake from git tags → FIRMWARE_VERSION, BUILD_DATE
• Factory reset: Hold GPIO13 button on cold boot → full parameter + log erase