FAQ
TL;DR: “Send page 1 and it must work” [Elektroda, Slawek K., #17619813]. A single page command fixes 90 % of navigation issues while 77 % SRAM usage already triggers instability warnings [Elektroda, darlin, post #18453905] Why it matters: mastering one-line serial commands prevents lock-ups and slashes debug time.
Quick Facts
• Default baud-rate: 9600 bps (set with `bauds=9600`) [Nextion Instr.Set].
• EEPROM size on Basic series: 1024 bytes, 4 bytes per `wepo` number [Elektroda, ekrzychoooo, post #17535690]
• Available GPIO lines on Enhanced/Intelligent: 8 (4 PWM-capable) [Nextion Instr.Set].
• RAM warning level: > 80 % global usage; Nano crash reported at 89 % [Elektroda, darlin, post #18453905]
• `tft` upload over UART: ~25 kB min⁻¹ at 115 kbaud [ITEAD Docs].
How do I change pages from Arduino?
Send a plain text command: Serial.print("page 2\xFF\xFF\xFF");. The triple 0xFF terminators are mandatory. Users confirmed it works on Uno, Mega and ESP when nexSerial matches the connected UART [Elektroda, Slawek K., #17619813].
The command `0x66 0x02` did nothing—why?
0x66 is a response from Nextion, not a command to it. Always use human-readable instructions (page, vis, click) followed by three 0xFF bytes when sending from the MCU [Nextion Instr.Set].
Why does my Dual-State Button reset after switching pages?
Local (vscope=local) attributes clear when you leave a page. Declare the val variable as global or copy it to a global va object before navigation, then reload it in the destination page’s Preinitialize event [Elektroda, ekrzychoooo, post #19364268]
How can I read which page is currently displayed?
Issue sendme from Arduino; Nextion replies with 0x66 0xPP 0xFF 0xFF 0xFF, where PP is the page ID. Parse the second byte to know the active page [Nextion Instr.Set].
My text flashes and returns `0x1A` errors—what’s wrong?
0x1A means “Invalid variable or attribute”. Check that object names and IDs in your Arduino code exactly match the HMI file; mismatched names (e.g., page0.n1 vs n1) caused this in several projects [Elektroda, rs6000, post #17434161]
Can I store multiple integers in EEPROM?
Yes—each wepo stores a 4-byte signed long. Address them at 4-byte intervals (0,4,8…). Using 6-byte spacing just wastes space and is not required [Elektroda, ekrzychoooo, post #17535690]
What’s the safest way to update a value only when it changes?
- Read the new value into
valNew.
- If
valNew != valPrev, send it with pageX.obj.val=valNew.
- Set
valPrev = valNew.
This cuts serial traffic by ~50 % in logging tests [Elektroda, Slawek K., #18690561].
Why does my Nano freeze after adding 30 objects?
Every declared Nextion object consumes SRAM. A user hit 89 % global RAM (1 592 B) with 35 objects, causing instability [Elektroda, darlin, post #18453905] Shorten object names and send raw serial strings instead of creating Nex* instances to cut memory use by up to 40 % [Elektroda, Slawek K., #18454973].
How do I invert a Progress Bar (countdown style)?
Set the bar value to 100-(curr*100)/total. Example for a 160-second timer: j0.val=100-(100*myTimer.val)/160 in the Timer event [Elektroda, ekrzychoooo, post #18898441]
Is it possible to overwrite the bootloader or font chip via SD?
No. The SD or UART uploader only writes the external SPI flash (25Q32) that stores the HMI project. The bootloader resides inside the STM32 and is read-protected [ITEAD Docs]. A white screen after upload usually means a corrupt TFT file, faulty SD slot, or dead backlight [Elektroda, janwoj111, post #20592222]
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