Temperature, brew timer and recovery-shaded charts for the Lelit Mara X espresso machine, running on an ESP32-S3 with a 3.5" QSPI touchscreen and built on ESPHome + LVGL.
Not affiliated with or endorsed by Lelit. Hobby project, MIT-licensed, use at your own risk — especially when wiring into the machine's UART.
Firmware works end-to-end on the jc3248w535 board. Still looking for:
- a nicer enclosure / mount for the display
- a clean PCB harness for the UART + power wiring into the Mara X
If you've designed something for this combo, open an issue or PR.
- Live steam / HX / target temperature readout with brew status
- Dual-resolution chart: 1 s sampling / 50 s window when brewing, 15 s / 15 min otherwise
- Auto-switch to high-res on brew start, back to low-res after adaptive recovery
- Shaded context bands on the chart: brew window (blue), recovery (green, 90 s)
- Shot timer at 100 ms precision (MM:SS.D), value persists after the pump stops
- Demo mode with simulated machine cycles when no UART is connected
- Touch controls to toggle resolution and demo mode
| Display Model | Status | Configuration File |
|---|---|---|
| jc3248w535 | ✅ Tested | jc3248w535-marax.yaml |
The board is an all-in-one ESP32-S3 module with a 3.5″ 480×320 QSPI
touchscreen — typically listed under search terms like "ESP32 S3 3.5
inch LCD Development Board 480x320 Display". Internally the panel is
driven by the qspi_dbi platform with the JC4832W535 model, which is
the closest panel ID in ESPHome's driver that drives this controller
correctly.
- The all-in-one board above (or an ESP32-S3-DevKitC-1 wired to a compatible 480×320 QSPI display)
- Touch controller: AXS15231
- UART connection to a Lelit Mara X
| Function | ESP32-S3 Pin |
|---|---|
| Display CLK | GPIO47 |
| Display Data | GPIO21, 48, 40, 39 |
| Display CS | GPIO45 |
| Display Backlight | GPIO1 |
| Touch SDA | GPIO4 |
| Touch SCL | GPIO8 |
| UART TX | GPIO43 |
| UART RX | GPIO44 |
Open https://elsbrock.github.io/esphome-marax/ in Chrome or Edge on desktop, plug your ESP32-S3 board in over USB and hit Install firmware. After flashing, the page walks you through WiFi setup via Improv-Serial. The firmware also exposes Improv over BLE as a fallback if the serial handshake misses the boot window — pair from a phone app or Chrome's Web Bluetooth.
WebSerial only works in Chromium-based browsers (Chrome, Edge, Opera) on desktop; Safari and Firefox can't flash this way.
-
Clone:
git clone https://github.com/elsbrock/esphome-marax.git cd esphome-marax -
Configure secrets:
cp secrets.yaml.example secrets.yaml # Fill in wifi_ssid, wifi_password, api_encryption_key, # ota_password and ap_password.
-
Flash:
esphome run jc3248w535-marax.yaml
If the device can't join your WiFi after flashing, it falls back to a
captive portal on the Marax-Display Fallback Hotspot SSID using
ap_password from your secrets.yaml. Subsequent updates can be sent
over the air via the ESPHome dashboard or Home Assistant.
jc3248w535-marax.yaml # Main hardware config + UART debug parser
config/
├── display_ui.yaml # LVGL pages and widgets
├── fonts.yaml # Fonts and Material Design icon glyphs
├── sensors.yaml # Templates, globals, time, wifi info
└── uart_parser.yaml # UART timeout + "NO DATA" blink (housekeeping)
includes/
├── chart_helpers.h # Chart data buffers, averaging, render path
├── chart_draw.h # Tick-label and shading event callbacks
└── timer_helpers.h # Shot timer formatting and flashing
The display reads UART at 9600 baud using inverted serial logic (this matters — the Mara X's serial line is inverted relative to standard TTL). Frames look like:
C1.06,116,124,093,0840,1,0\n
| Field | Meaning |
|---|---|
C1.06 |
Firmware version |
116 |
Steam temperature (°C) |
124 |
Target temperature (°C) |
093 |
HX temperature (°C) |
0840 |
Timer/timestamp (unused here) |
1 |
Heating element on/off |
0 |
Pump on/off |
The device is built on ESPHome's API, so once it shows up under the ESPHome integration in Home Assistant you get the following entities out of the box:
| Entity | Unit | What it is |
|---|---|---|
sensor.steam_temperature |
°C | Steam boiler actual temperature |
sensor.service_temperature |
°C | Steam boiler setpoint (firmware-configured target) |
sensor.hx_temperature |
°C | Brew group (heat exchanger) temperature |
text_sensor.mara_x_version |
— | Firmware version reported by the machine |
text_sensor.mara_x_raw_data |
— | Last raw UART frame, useful for debugging |
Enough to drive simple automations — e.g. a phone notification when the brew group reaches operating temperature:
automation:
- alias: "Mara X ready"
trigger:
platform: numeric_state
entity_id: sensor.hx_temperature
above: 88
for: "00:00:30" # avoid bouncing if HX dips below briefly
action:
service: notify.mobile_app_your_phone
data:
title: "☕ Mara X"
message: "Brew group is up to temperature."The UART link is read-only — the firmware does not (and cannot) send commands back to the machine.
- Top bar: title, machine status, time, UART signal, WiFi status
- Left panel: shot timer, temperature readings (Steam / Target / HX), version, heat + pump indicators
- Right area: live temperature chart with shaded brew/recovery bands
- Red line: steam temperature
- Blue line: HX/brew temperature
- Green line: target temperature
- Dotted grid; tick labels formatted by a chart draw-event callback
- Time scale: 50 s window in high-res, 15 min window in low-res
- Shaded brew window (blue) and recovery (green, 90 s) bands behind the series
- Auto-switches to high-res on pump start; reverts to low-res once recovery is detected
- Resolution change backfills high-res buffer from the raw data ring, so there's no left-edge gap
- Right edge, mid-screen (~y = 100–180): toggle demo mode (a hidden hit-strip; the UART icon up top is not the target)
- Chart area: switch between 1 s and 15 s resolution
- Demo mode auto-disables as soon as a real UART frame arrives
- A recent ESPHome (built and tested on 2026.2.x; needs
uart.debug.sequencewhich has been available for years) - ESP-IDF framework (selected via the YAML)
Demo mode — synthetic data with a small state machine:
- ~60 s cold start-up
- ~5 min ramp to operating temperature
- READY at operating temperature, then a brew cycle every ~30 s after recovery
- Auto-disables when real UART data arrives
No-data mode — when the UART has gone quiet for 5 s:
- Blinking "NO DATA" status
- Temperature readouts show
--°C - Resumes automatically when the Mara X reconnects
- UART parsing is event-driven via
uart.debug.sequencewith a\ndelimiter — no 10 Hz polling loop update_temperature_displayscaches the last rendered integer value and color band per widget, so labels and styles only get re-applied when something actually changed (otherwise every LVGL setter would invalidate the widget on every 400 ms frame)- Chart shading and tick labels are drawn from
LV_EVENT_DRAW_PART_END/LV_EVENT_DRAW_PART_BEGINcallbacks; each is scoped to just the part it cares about - LVGL draw buffer is sized to fit in internal SRAM rather than PSRAM (faster pixel pushes)
- Verify TX/RX wiring
- Confirm
inverted: trueis set on the UART pins — the Mara X's line is not standard TTL polarity - Watch
maraxlog lines; the parser logs each parsed frame at debug level
- PSRAM must be enabled and configured for octal mode (see
psram:block in main YAML) - Check QSPI pin wiring against the table above
- Touch I²C: SDA on GPIO4, SCL on GPIO8
The render path is gated in several places — if you're modifying it, watch for:
- The Y-axis range applies 2 °C hysteresis before rescaling, so small jitter is absorbed
get_averaged_temp_at_timewalks the raw buffer backward and stops at the first out-of-window sample (O(k), not O(n))- Label setters in
update_temperature_displaysare no-ops when the integer reading and color band haven't changed - The chart is not torn down on brew start / resolution toggle; just the point buffer is resized and the data is refilled
PRs welcome. Keep changes minimal and conventional-commit-style; a short description of the why (especially for perf-sensitive code) is more valuable than a wall of restated diff.
MIT — see LICENSE.