Ghost Hand

{
 "title": "Ghost Hand calcs",
 "rev": "2",
 "date": "2026-11-08",
 "charger": {
  "rprog_ohm": 13000.0,
  "i_reg_mA": 76.9,
  "c_rate": 0.51,
  "charge_time_h": 2.44,
  "p_worst_W": 0.135,
  "rise_minimal_copper_C": 31.0,
  "note": "0.51 C: inside the pack's 1 C quick-charge limit (QA.S.0228 form 1), and 4 x less heat in U2 than rev 1"
 },
 "stat_divider": {
  "r_top": 68000.0,
  "r_bot": 100000.0,
  "v_at_4v75": 2.83,
  "v_at_5v0": 2.98,
  "v_at_5v5": 3.27,
  "vih_ok": true,
  "abs_max_ok": true
 },
 "vbus_sense_divider": {
  "r_top": 100000.0,
  "r_bot": 150000.0,
  "v_at_4v75": 2.85,
  "v_at_5v0": 3.0,
  "v_at_5v5": 3.3,
  "vih_ok": true,
  "abs_max_ok": true
 },
 "ldo": {
  "iq_nA": 25,
  "i_rail_peak_mA": 48.1,
  "dropout_at_peak_mV": 64.9,
  "min_vbat_for_3v3": 3.365,
  "note": "the firmware stops at 3.45 V, above the dropout point"
 },
 "vbat_monitor": {
  "divider": "4.7M / 4.7M to GND, always on",
  "v_adc_full": 2.1,
  "ref_V": 2.5,
  "lsb_mV_at_vbat": 4.88,
  "sleep_leak_uA": 0.45,
  "settle_ms": 235,
  "note": "VBAT/2 stays under 2.1 V, inside the 3.3 V rail; C6 (100 nF) holds it for the ADC sample"
 },
 "receiver": {
  "tia_rf_ohm": 150000.0,
  "tia_cf_F": 4.7e-12,
  "tia_bw_kHz": 225.8,
  "hp_corner_kHz": 1.59,
  "stage2_gain": 11,
  "comparator": "AC0 AINP0 (PA7) vs DACREF, threshold RX_REF + 60 mV by default, adapted to the noise floor",
  "cases": [
   {
    "distance_in": 3,
    "off_axis_deg": 0,
    "irradiance_mW_cm2": 0.8611,
    "photo_uA": 12.056,
    "tia_mV": 1808.3,
    "rx_sig_mV": 3000.0
   },
   {
    "distance_in": 3,
    "off_axis_deg": 30,
    "irradiance_mW_cm2": 0.6097,
    "photo_uA": 8.536,
    "tia_mV": 1280.4,
    "rx_sig_mV": 3000.0
   },
   {
    "distance_in": 5.5,
    "off_axis_deg": 0,
    "irradiance_mW_cm2": 0.2562,
    "photo_uA": 3.587,
    "tia_mV": 538.0,
    "rx_sig_mV": 3000.0
   },
   {
    "distance_in": 5.5,
    "off_axis_deg": 30,
    "irradiance_mW_cm2": 0.1814,
    "photo_uA": 2.54,
    "tia_mV": 381.0,
    "rx_sig_mV": 3000.0
   },
   {
    "distance_in": 12,
    "off_axis_deg": 0,
    "irradiance_mW_cm2": 0.0538,
    "photo_uA": 0.753,
    "tia_mV": 113.0,
    "rx_sig_mV": 1243.0
   },
   {
    "distance_in": 12,
    "off_axis_deg": 30,
    "irradiance_mW_cm2": 0.0381,
    "photo_uA": 0.534,
    "tia_mV": 80.0,
    "rx_sig_mV": 880.0
   }
  ],
  "assumed": "faucet emitter 50 mW/sr peak; real units vary 10 to 200 mW/sr, the firmware sets the threshold from what it sees"
 },
 "echo": {
  "emitters": {
   "VSMY2853SL_850nm": {
    "vf_at_pulse_V": 1.8,
    "r_series_ohm": 8.2,
    "i_peak_mA": [
     200,
     292
    ],
    "ie_mW_sr": [
     100,
     146
    ],
    "limit": "IFSM 1 A at tp = 100 us; pulses are 25 us at under 2 % duty"
   },
   "VSMB2948SL_940nm": {
    "vf_at_pulse_V": 1.7,
    "r_series_ohm": 4.7,
    "i_peak_mA": [
     371,
     531
    ],
    "ie_mW_sr": [
     74,
     106
    ],
    "limit": "IFSM 1 A at tp = 100 us; pulses are 25 us at under 2 % duty"
   }
  },
  "pulse_us": 25,
  "total_peak_mA_at_full": 823,
  "hand_return_W_m2": 0.1045,
  "echo_850_W_m2_at_12in": 1.0764,
  "echo_940_W_m2_at_12in": 0.7965,
  "margin_vs_hand_at_12in_850": 10.3,
  "margin_vs_hand_at_12in_940": 7.6,
  "note": "the echo arrives inside the faucet's own pulse, so a synchronous receiver reads it as a strong reflection"
 },
 "battery_life": {
  "battery": "Adafruit 1317, 150 mAh 1S LiPo",
  "usable_mAh": 128,
  "stop_V": 3.45,
  "sleep_uA": {
   "TPS7A0233 IQ": 0.025,
   "ATtiny1616 power-down, pin-change wake on PA2 and PB2": 0.1,
   "LIS2DW12 LP mode 1, 12.5 Hz, wake-up detection": 1.0,
   "MCP73831 reverse discharge (no VBUS)": 0.15,
   "VBAT monitor divider, 9.4 Mohm": 0.42,
   "WS2812B rail switched off (Q3)": 0.0,
   "TLV9062 unpowered (PA4 low)": 0.0,
   "LiPo pack protection IC S-8261AAJMD (3 uA assumed)": 3.0
  },
  "sleep_total_uA": 4.7,
  "sleep_only_years": 3.1,
  "active_mA": {
   "ATtiny1616 standby with OSC20M at 5 MHz for AC + TCB (idle 0.6 mA at 3 V) plus wake-ups": 0.8,
   "TLV9062 two channels (538 uA each typ)": 1.08,
   "receiver bias divider 3.3 V / 110 k": 0.03,
   "IR echo pulses (850 + 940 nm emitters, 25 us at 20 Hz)": 0.411,
   "status dot: breathing at 2 % average white, 20 % rail duty": 0.6,
   "LIS2DW12 LP 50 Hz (pick-up and tilt watch)": 0.004
  },
  "active_total_mA": 2.93,
  "hours_of_running": 44.0,
  "mAh_per_10min_session": 0.488,
  "sessions_per_charge": 261,
  "days_per_charge": {
   "1 session a day": 170,
   "3 sessions a day": 74,
   "6 sessions a day": 40
  },
  "self_discharge": "3.0 %/month assumed (0.15 mAh/day), larger than the sleep current",
  "charge_time_h": 2.44,
  "days_per_charge_min_capacity": {
   "6 sessions a day": 38,
   "3 sessions a day": 70
  },
  "once_a_month_bar": {
   "sessions_per_day_for_30_days": 8.2
  },
  "pulse_supply": "the 0.93 A, 25 us echo pulse comes mostly from C15 (100 uF); the pack's average load is about 3 mA, far under its 150 mA (1 C) continuous rating",
  "note": "typical datasheet currents at 25 C; the faucet's pulse rate and the light pattern are the two big unknowns"
 },
 "timing": {
  "session_cap_s": 600,
  "settle_after_set_down_s": 1.5,
  "listen_before_echo_s": 2.0,
  "default_rearm_s": 8.0,
  "blip_start_ms": 600,
  "blip_min_ms": 120,
  "blip_step": 0.85,
  "rearm_margin_s": 1.5,
  "timeout_window_s": [
   10,
   60
  ],
  "pickup_g": 0.25,
  "tilt_deg": 30,
  "low_battery_V": 3.45,
  "note": "re-arm proactively at (learned timeout - margin); shorten the blip by 15 % each time the faucet stays on, lengthen 30 % when it misses"
 },
 "hot": {
  "U2": {
   "W": 0.135,
   "why": "MCP73831 linear charger at 77 mA, VBUS 5.25 V, cell 3.5 V"
  },
  "U3": {
   "W": 0.0433,
   "why": "LDO at the peak light current"
  }
 }
}