# RoastIQ Temp Sensor — Circuit Reference

Wiring guide for soldering the ESP32 dual-thermocouple temperature sensor board.

---

## Bill of Materials

| Qty | Component              | Notes                              |
|-----|------------------------|------------------------------------|
| 1   | ESP32 DoIt DevKit v1   | 38-pin, USB powered                |
| 2   | MAX6675 module         | With screw terminals or pin header |
| 2   | K-Type thermocouple    | One for BT (bean), one for ET (exhaust) |
| —   | 22 AWG hookup wire     | 6 colours recommended for clarity  |
| —   | Breadboard or perfboard| Breadboard for prototyping, perfboard for permanent build |

---

## Wiring Diagram

```
  ┌──────────────────────────────────────────────────────────────────┐
  │              RoastIQ Ventures Temp Sensor — Wiring                │
  │                                                                  │
  │                      SPI Bus 1 — BT (Bean Temperature)          │
  │   ┌────────────┐  GPIO 5  ─────────────────── SCLK              │
  │   │            │  GPIO 23 ─────────────────── CS    ┌─────────┐ │
  │   │   ESP32    │  GPIO 19 ◄────────────────── SO    │MAX6675  │ │
  │   │  DevKit v1 │  3V3     ─────────────────── VCC   │  #1     │ │
  │   │            │  GND     ─────────────────── GND   │  (BT)   │ │
  │   │            │                                    │         │ │
  │   │            │                                    │  T+  T- │ │
  │   │            │                                    └───┬──┬──┘ │
  │   │            │                                        │  │    │
  │   │            │                                  ┌─────┴──┴──┐ │
  │   │            │                                  │  K-Type   │ │
  │   │            │                                  │  Probe    │ │
  │   │            │                                  │   (BT)    │ │
  │   │            │                                  └───────────┘ │
  │   │            │                                                 │
  │   │            │      SPI Bus 2 — ET (Exhaust Temperature)      │
  │   │            │  GPIO 26 ─────────────────── SCLK              │
  │   │            │  GPIO 25 ─────────────────── CS    ┌─────────┐ │
  │   │            │  GPIO 33 ◄────────────────── SO    │MAX6675  │ │
  │   │            │  3V3     ─────────────────── VCC   │  #2     │ │
  │   │            │  GND     ─────────────────── GND   │  (ET)   │ │
  │   └────────────┘                                    │         │ │
  │                                                     │  T+  T- │ │
  │                                                     └───┬──┬──┘ │
  │                                                         │  │    │
  │                                                   ┌─────┴──┴──┐ │
  │                                                   │  K-Type   │ │
  │                                                   │  Probe    │ │
  │                                                   │   (ET)    │ │
  │                                                   └───────────┘ │
  └──────────────────────────────────────────────────────────────────┘
```

---

## Pin Reference — Soldering Cheatsheet

### MAX6675 #1 — BT (Bean Temperature)

| ESP32 Label | GPIO | → | MAX6675 Pin |
|-------------|------|---|-------------|
| 3V3         | —    | → | VCC         |
| GND         | —    | → | GND         |
| D5          | 5    | → | SCLK        |
| D23         | 23   | → | CS          |
| D19         | 19   | ← | SO          |

### MAX6675 #2 — ET (Exhaust Temperature)

| ESP32 Label | GPIO | → | MAX6675 Pin |
|-------------|------|---|-------------|
| 3V3         | —    | → | VCC         |
| GND         | —    | → | GND         |
| D26         | 26   | → | SCLK        |
| D25         | 25   | → | CS          |
| D33         | 33   | ← | SO          |

> `→` = ESP32 drives the signal  `←` = ESP32 reads the signal

---

## Power

- MAX6675 runs on **3.3 V** — use the ESP32's **3V3** pin, **not VIN or 5V**
- Both modules share the same 3V3 and GND rails
- The ESP32 is USB-powered; no external supply is needed for bench testing
- Total current draw of both MAX6675 modules is under 10 mA — well within the 3V3 regulator limit

---

## Thermocouple Wiring (K-Type)

K-Type thermocouples have two conductors. Connect them to the screw terminals on the MAX6675 module:

| Thermocouple wire | MAX6675 terminal |
|-------------------|------------------|
| **Yellow / (+)**  | T+               |
| **Red / (−)**     | T−               |

> Colour codes vary by manufacturer. When in doubt, check the label on the probe or its datasheet.
> Reversing polarity gives inverted readings, not damage.

- Route thermocouple leads away from mains wiring to reduce noise
- If the MAX6675 detects an open (disconnected) thermocouple it reports **1023.75 °C** — the firmware checks this bit

---

## Soldering Tips

1. **Tin all wire ends** before soldering to module headers
2. **Use flux** — MAX6675 module pads are small and flux prevents cold joints
3. After soldering, **verify continuity** with a multimeter before powering up:
   - Each signal wire point-to-point (e.g. D5 → SCLK of #1)
   - No shorts between adjacent pins
4. **Common fault — 1023.75 °C reading**: SO or CS wire is loose or swapped
5. **Common fault — 0 °C reading**: VCC or GND missing; probe not connected
6. **Common fault — both channels identical**: CLK or CS wires crossed between modules

---

## Firmware Reference

Pin definitions are in [`src/main.cpp`](src/main.cpp):

```cpp
// MAX6675 #1 — BT
int thermoDO  = 19;   // SO
int thermoCS  = 23;   // CS
int thermoCLK = 5;    // SCLK

// MAX6675 #2 — ET
int thermoDO2  = 33;  // SO
int thermoCS2  = 25;  // CS
int thermoCLK2 = 26;  // SCLK
```

Data is read every 3 seconds and broadcast over WebSocket at `ws://<ESP32_IP>:80/ws`
in the format `{"data": {"BT": 185.5, "ET": 210.25}}`.