# Arcarix Studio — Room climate monitor

> UNVERIFIED EXAMPLE / Output of a rule-based demo. Not a quotation, fabrication package or test result.

## Idea
> "We’re developing an indoor temperature and humidity sensor for businesses with multiple locations. Staff need to check each site from a phone."

## Requirements
- Power: USB 5 V (default · to confirm)
- Link: Wi-Fi (from the sentence)
- Interval: 30s (default · to confirm)
- Environment: indoor (from the sentence)
- Target quantity: 100 (default · to confirm)
- Note (does not alter the design): —

## Chip
- ESP32-C3-MINI-1 (recommended)

## Checks
- [PASS] The chip supports the Wi-Fi requirement.
- [PASS] All parts share 3.3 V logic.
- [PASS] No I²C address conflict (SHT31 at 0x44).
- [PASS] Needs 6 GPIO · about 15 available.
- [PASS] USB 5 V → 3.3 V 600 mA LDO leaves headroom for radio peaks.
- [WARN] Radio products need certification (e.g. KC, FCC) before sale; priced separately.

## PCB
- 50 × 34 mm · 2-layer · SMT 18 placements (concept layout)

## Enclosure
- 3D printing · FDM (PETG) · 57 × 41 × 14.8 mm · wall 2 mm

## BOM
- U1 ESP32-C3-MINI-1 × 1 — USD 2.40 (RISC-V · 160 MHz · radio module)
- U2 SHT31-DIS × 1 — USD 2.90 (I²C temperature/RH sensor · address 0x44)
- R1–R2 10 kΩ 0402 × 2 — USD 0.01 (I²C pull-ups)
- J1 USB-C 16P × 1 — USD 0.35 (5 V input receptacle)
- U3 LDO 3.3 V 600 mA × 1 — USD 0.18 (SOT-23-5 regulator)
- D1 USB ESD array × 1 — USD 0.12 (ESD protection)
- R3–R4 5.1 kΩ 0402 × 2 — USD 0.01 (USB-C CC resistors)
- D2 LED 0603 × 1 — USD 0.03 (Status indicator)
- SW1–SW2 Tact switch 3×4 × 2 — USD 0.10 (Reset · boot)
- C1–C6 100 nF / 10 µF × 6 — USD 0.01 (Decoupling and bulk capacitors)
- H1–H4 M2 × 6 screw × 4 — USD 0.04 (PCB and lid fastening)

## Illustrative estimate (assumptions, quantity 100)
- Components (BOM): $5.05
- PCB fabrication: $0.60
- PCB assembly: $0.92
- Enclosure: $6.32
- Assembly labour: $1.80
- Flashing & functional test: $0.48
- Packaging: $1.20
- Contingency 8%: $1.31
- One-time costs: $470.00 (PCB fabrication setup, SMT stencil and programming, Test jig)
- **Unit cost: $22.37** · Price at target margin (margin 40%): $37.29
- Excludes electronics, firmware and mechanical engineering fees, certification, shipping, duties, app/cloud development and marketing

## Production
- Pilot run · 7.7 min/unit · about 52 units per operator per day

## Firmware skeleton
```c
// Arcarix Studio — FIRMWARE SKELETON (not compiled, not tested)
// Target  : ESP32-C3-MINI-1
// Sensor  : SHT31 (I2C 0x44)
// Link    : Wi-Fi · Power: USB 5 V · Interval: 30 s
// Pin map : example assignment — confirm strapping pins in the datasheet

#define PIN_SDA       /* GPIO4 */
#define PIN_SCL       /* GPIO5 */
#define PIN_LED       /* GPIO3 */
#define INTERVAL_S 30
#define MAX_RETRIES 3

void setup() {
  status_led_begin(PIN_LED);
  sht31_begin(PIN_SDA, PIN_SCL, 0x44);
  wifi_connect(WIFI_SSID, WIFI_PASS);   // from provisioning, never hard-coded
}

void loop() {
  Reading r = sht31_read();
  for (int i = 0; i < MAX_RETRIES && !r.ok; i++) {
    delay_ms(200 << i);                   // bounded back-off
    r = sht31_read();
  }
  if (!r.ok) { record_fault(SENSOR_TIMEOUT); }
  else {
    publish_https("/v1/readings", r);
  }
  wait_seconds(INTERVAL_S);
}
```

## Next steps
Circuit review, bench testing and real component and manufacturing quotes are required. No external submission or order has occurred.

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