arduino-knobs-brightness-contrast

ADC knobs → brightness / contrast (ESP32 / ESP8266)

monitor_knobs_http.ino reads two analog inputs on ESP32 (pots or dividers), maps them to integers, and sends STATset BRIGHTNESS / STATset CONTRAST by calling MonitorControl.Web over WiFi (POST /api/vmc/set). On ESP8266, only A0 is a true ADC — the sketch still compiles and posts both tokens, but both values come from the same pin unless you add an external ADC (for example ADS1115) and change readMapped for the contrast channel.

Why HTTP instead of raw SDCP on the MCU?

SDCP uses a binary V3 header + item 0xB000 payload layout (framing doc). Implementing that correctly on Arduino is possible but error-prone. A small LAN PC, NUC, or Raspberry Pi running dotnet run --project src/MonitorControl.Web is the simplest bridge: the MCU only needs WiFi + JSON.

Wiring

• 3.3 V MCUs: connect pot ends to 3V3 and GND, wiper to ADC_BRIGHT_PIN / ADC_CONTRAST_PIN (defaults in sketch).
• Add a 100 nF–1 µF cap from each wiper to GND to quiet ADC noise if cables are long.
• ESP8266 has a 0–1 V ADC range on the TOUT pin on some modules; many dev boards use a voltage divider — check your board and adjust ADC_MAX.

Calibration (NVS / EEPROM)

After flashing, open the serial monitor at 115200 baud:

• Put the brightness pot at its physical minimum, then send cap bmin. Repeat at maximum with cap bmax.
• Same for contrast: cap cmin, cap cmax.
• cal show prints stored ADC endpoints; cal reset restores full-scale mapping.

ESP32 uses Preferences (kbcal namespace). ESP8266 uses a small EEPROM blob.

Configure the sketch

Edit the /* ---- User configuration ---- */ block:

Define	Meaning
WIFI_SSID / WIFI_PASSWORD	LAN credentials
GATEWAY_HOST	IP of the machine running MonitorControl.Web (not necessarily the monitor)
GATEWAY_PORT	Usually 5080
MONITOR_HOST	Monitor’s SDCP IP (same value you use in the web UI “host”)
ADC_* pins and VMC_*_MIN / MAX	Range your chassis accepts (try get BRIGHTNESS from CLI/UI first)

Run the gateway

dotnet run --project src/MonitorControl.Web --urls http://0.0.0.0:5080

Bind to 0.0.0.0 so devices on the LAN can reach the API (firewall permitting).

Flow diagrams

See docs/diagrams/monitor-control-flows.md — Physical UI section compares this HTTP path to the ESP32 native TCP path.

ESP32: native SDCP alternative

On ESP32 only, you can skip HTTP entirely and speak SDCP v3 on TCP 53484 from the firmware (examples/esp32-sdcp-vmc/, monitor_knobs_sdcp.ino). That trades gateway simplicity for wire-format maintenance in C++. Use HTTP (this sketch) when you want ESP8266, centralized auth, or minimal on-device protocol code.

Live push (SSE / WebSocket)

This sketch only uses POST /api/vmc/set. For SSE or WebSocket live snapshots, use the bundled web UI on MonitorControl.Web or call those endpoints yourself. If you run the Python gateway on :8000, SSE for /api/events/... is proxied; WebSocket must still target the .NET port (see examples/python-service/README.md).