CYD_Doodler

A multi-unit social toy for the Cheap Yellow Display (CYD). Flash the same sketch to two or more units and they discover each other over ESP-NOW — no router, no WiFi join, no pairing — and form a connectionless mesh.

What the units share with each other:

• Shared whiteboard. Draw on the black canvas and your strokes stream live to every peer as vector segments, replaying on their screens. A spectrum + greyscale color picker runs along the bottom; "clear" (top-right) wipes the canvas on every unit.
• Emoji reactions. Tap an emoji in the bottom toolbar to broadcast it. Every unit shows it big and centered for a couple of seconds and plays a little per-emoji jingle through the speaker.
• Proximity. Each unit estimates how close its peers are from the radio signal strength (RSSI) of their packets, smoothed over time, and shows near/far on the tools screen.
• Editable 3-character id per unit, saved to flash so it survives reboots.

The top-left corner toggles between the home (doodle) view and the tools view.

Hardware

You need two or more CYD units to see anything interesting — a single unit just talks to nobody.

• Board: Cheap Yellow Display, ESP32-2432S028 (ESP32S, no PSRAM). These are sold under many names; look for the 2.8" 320×240 SPI TFT with a resistive touch panel and an ESP32 on the back.
• Speaker (optional): the on-board amplifier on GPIO 26 plays the emoji jingles. Everything else works without it.

⚠️ Display-driver variant trap. CYD boards ship with one of two TFT panels — ILI9341 or ST7789 — and which one you have does not reliably track the USB-connector count or the box label. This project's reference unit is ILI9341. If your screen is blank, garbled, mirrored, or badly mis-colored, you have the other panel — set the driver to ST7789 in your TFT_eSPI setup (see below).

Pinout (fixed on the CYD board)

Function	Pins
Display (SPI)	MISO 12 · MOSI 13 · SCLK 14 · CS 15 · DC 2 · RST −1 · BL 21
Touch (XPT2046)	CLK 25 · MISO 39 · MOSI 32 · CS 33 · IRQ 36 (own SPI bus)
Speaker amp	GPIO 26

Software setup

1. Arduino IDE + ESP32 core

Install the Arduino IDE and add the ESP32 board package (3.x) via Boards Manager.

2. Libraries (Library Manager)

• TFT_eSPI (display)
• XPT2046_Touchscreen (touch)

WiFi, esp_now, esp_wifi, and Preferences are part of the ESP32 core — no separate install.

3. Configure TFT_eSPI for the CYD

TFT_eSPI is configured by editing a setup header inside the library itself, not from this sketch — so if you already have a working CYD setup, it'll just work. If you're starting fresh, the community reference ESP32-Cheap-Yellow-Display has step-by-step display-config instructions (and ready-made setup files) for this exact board.

The only project-specific things to get right:

• Driver: select ILI9341 (this project's reference unit) or ST7789 for your panel — see the variant note above. If the screen is blank, garbled, mirrored, or mis-colored, switch to the other one.
• Pins: use the display pins from the Pinout table above.
• Touch: leave touch unconfigured in TFT_eSPI — this sketch drives the XPT2046 panel separately via the XPT2046_Touchscreen library.

4. Build & flash

1. Open CYD_Doodler.ino in the Arduino IDE. (The .ino filename must match its folder name — keep the folder called CYD_Doodler.)
2. Select board ESP32 Dev Module and the right serial port.
3. The default partition scheme is fine (this sketch has no BLE; the binary is small).
4. Upload. Serial monitor runs at 115200.

Flash the same sketch to every unit.

Using it

• All units must agree on WIFI_CHANNEL (top of the sketch, default 1). If your units can't see each other, check they're on the same channel.
• ESP-NOW is single-hop: units have to be within direct radio range.
• On first boot each unit picks a random-ish 3-char id from its MAC. Tap the top-left corner to open the tools screen and edit it with the up/down arrows; it's saved to flash.

Project layout

File	What it is
CYD_Doodler.ino	The whole sketch.
doodler_types.h	Shared structs/enums (kept in a header on purpose — see the note at its top).

How it works

A few project-specific notes if you want to hack on it:

• Transport. Pure ESP-NOW broadcast — WiFi.mode(WIFI_STA) + WiFi.disconnect() + a fixed channel; it never joins an access point. Each unit beacons a few times a second to the broadcast peer FF:FF:FF:FF:FF:FF. There's no SSID or password anywhere.
• Receive path. The recv callback (core-3.x signature, onRecv(const esp_now_recv_info_t*, const uint8_t*, int)) runs in the WiFi task, not the main loop. Per-packet RSSI comes from info->rx_ctrl->rssi and the sender MAC from info->src_addr. The callback only touches shared state (the peer table and stroke buffer) inside a portMUX critical section; all TFT drawing happens in loop() to keep it off the WiFi task.
• Rendering. No PSRAM, so a full 320×240 16-bit sprite won't allocate. The framebuffer is an 8-bit TFT_eSprite (~75 KB); each frame composites into it and pushSprite()s once to avoid flicker. Canvas/pen color is therefore 8-bit (3-3-2, ≈256 colors), and a pen color travels over the air as a single packed byte.
• Types live in doodler_types.h on purpose. Once the .ino contains template functions, the Arduino IDE injects auto-generated prototypes at the very top of the file — above any type defined in the .ino — so any struct/enum used in a function signature must live in the header, or you get "not declared in this scope" errors.
• Persistence. The 3-char id is saved with Preferences (NVS), namespace "doodler", key "name".
• Sound. tone(26, …) / noTone(26); jingles are short blocking note sequences, which is fine for occasional events.

License

MIT — free to use, modify, and redistribute; please keep the copyright and license notice. Copyright © 2026 Gabriel M Schuyler.