V+A's Coffee Probe

An ESP32-C6 temperature monitor for coffee roasting / brewing. It reads a DS18B20 probe once per second, keeps up to an hour of history, shows live statistics on a 20x4 I2C LCD, and serves an interactive web chart over its own Wi-Fi access point.

Features

• DS18B20 1-Wire probe, 12-bit (0.0625 °C) resolution, read non-blocking.
• Rolling history of up to 3600 samples (1 hour at 1 Hz).
• Selectable averaging windows: 10, 60, 300, 600, 1800 and 3600 seconds.
• 20x4 I2C LCD showing current, average, delta, min and max for the window.
• SoftAP with a web dashboard: interactive Chart.js line chart plus a now/avg/min/max readout.
• Auto-recovers if the probe is missing or unplugged (re-scans every 5 s).
• Optional timestamped serial debug logging.

Hardware

Part	Connection
ESP32-C6-DevKitC-1	—
20x4 I2C LCD (PCF8574 backpack, addr 0x27)	SDA → GPIO6, SCL → GPIO7, VCC → 3V3, GND → GND
Push button	GPIO10 → GND (uses internal pull-up)
DS18B20	DQ → GPIO11, VDD → 3V3, GND → GND, 4.7 kΩ pull-up from DQ to 3V3

Notes for the ESP32-C6-DevKitC-1:

• GPIO6/GPIO7 are the default LP_I2C pins and are broken out on J1 (pins 5/6).
• Avoid GPIO12/13 (native USB D-/D+) and the strapping pins GPIO4/5/8/9/15.
• GPIO14 and GPIO27 are not exposed on this board.

The DS18B20 is used in normal 3-wire mode (not parasitic power).

Building and flashing

Requires PlatformIO. The ESP32-C6 needs the pioarduino espressif32 platform (v7.x or newer).

pio run              # build
pio run -t upload    # flash
pio device monitor   # serial monitor (115200 baud)

This project uses a custom partitions.csv (3 MB per OTA app slot) because the Wi-Fi stack plus the embedded Chart.js page exceed the default 1.25 MB app partition. Because the partition layout differs from the stock one, erase the flash once before the first upload:

pio run -t erase && pio run -t upload

Configuration

Build switches at the top of src/main.cpp:

Switch	Default	Effect
USE_DISPLAY	1	Set to 0 to run headless (skips I2C/LCD entirely)
USE_WIFI	1	Set to 0 to disable the SoftAP and web dashboard
DEBUG_SERIAL	0	Set to 1 for timestamped DBG(...) logging

USE_DISPLAY and USE_WIFI can also be overridden at build time, e.g. pio run -e esp32-c6-devkitc-1 with PLATFORMIO_BUILD_FLAGS=-DUSE_DISPLAY=0.

Other tunables in src/main.cpp:

• TIMES[] — averaging windows in seconds.
• MAX_TEMPERATURES — history depth (default 3600).
• SAMPLE_INTERVAL_MS — sampling period (default 1000 ms).
• CONVERSION_MS — DS18B20 conversion time; tied to the 12-bit resolution (750 ms). Adjust if you change setResolution().
• LONG_PRESS_MS — hold time to clear the stats (default 1000 ms).
• AP_SSID / AP_PASSWORD — SoftAP credentials.
• PIN_SDA, PIN_SCL, PIN_BUTTON, PIN_ONEWIRE.

Temperatures are stored internally in tenths of a degree Celsius (int16_t).

Usage

Button

• Short press — cycle the averaging window through 10 / 60 / 300 / 600 / 1800 / 3600 s.
• Long press (≥ 1 s) — clear the recorded history; all statistics restart.

LCD (20x4)

+--------------------+
| V+A's Coffee Probe |   row 0: static, centred title
| Cur  21.4°  n 3600 |   row 1: current temperature, window size (s)
| Avg  21.2° Δ  0.3° |   row 2: window average, delta since window start
| Max  22.0° Min 20.8°|  row 3: window max / min
+--------------------+

Status messages (Stats cleared, DS18B20 missing) are shown on the 3rd line.

Web dashboard

Join the Wi-Fi network V-A Coffee Probe (password coffeeprobe by default) and open http://192.168.4.1/. The page refreshes every 5 seconds.

Route	Description
/	Dashboard (chart + stats)
/chart.js	Embedded Chart.js 4.4.4 (205 KB, served from flash)
/data	{"interval":1,"temps":[tenths-of-°C,...]}

Chart rendering happens in the browser, so it costs the device no memory. The access point has no internet connection, which is why Chart.js is embedded rather than loaded from a CDN.

Memory

Measured on the ESP32-C6-DevKitC-1 with USE_WIFI=1, USE_DISPLAY=1:

RAM:   13.7% (44924 / 327680 bytes)   static, before runtime Wi-Fi heap
Flash: 40.8% (1282808 / 3145728 bytes) in a 3 MB app slot

• History: up to 3600 × int16_t ≈ 8 KB heap.
• /data response: ~20 KB JSON for a full hour, built in a reserve()d String (~22 KB peak heap).
• Wi-Fi SoftAP stack: roughly 50–80 KB heap.

Project layout

platformio.ini        PlatformIO environment and library dependencies
partitions.csv        Custom 8 MB flash partition table (3 MB OTA slots)
src/main.cpp          Firmware
include/chart_js.h    Chart.js 4.4.4 UMD minified, embedded as PROGMEM
include/index_html.h  Web dashboard HTML/JS, embedded as PROGMEM
nonet.py              Original MicroPython prototype (reference)

Dependencies

• LiquidCrystal_I2C 1.1.4
• OneWire — pinned to a commit with ESP32-C6 GPIO support (release 2.3.8 does not build for the C6)
• DallasTemperature 3.11.0
• Chart.js 4.4.4 (embedded)