FAQ
TL;DR: Use 4‑bit HD44780 character LCDs first—“This saves us 4 pins!”—and add an I2C/SPI backpack later; 4‑bit mode cuts data lines by 50%. Best free primers are linked below, with wiring and libraries ready to go. “Saving you weeks” for student assistive‑tech builds. “This saves us 4 pins!” [“Wiring a Character LCD | Adafruit Learning System”]
Why it matters: This FAQ helps students and makers pick fast, low‑risk LCD paths for head‑switch assistive projects.
Quick Facts
- 4‑bit HD44780 uses 6 MCU GPIO signals (RS, EN, D7–D4; RW tied low) for write‑only control. [“Wiring a Character LCD | Adafruit Learning System”]
- I2C/SPI LCD backpacks save 4 pins on character LCDs; not compatible with graphic LCDs. [“I2C/SPI LCD Backpack | Adafruit Learning System”]
- Typical character‑LCD logic: 5 V, ~1–1.5 mA; backlight often 32–60 mA (spec‑dependent). [Crystalfontz CFah1602SYH datasheet page]
- KS0108 128×64 graphic LCDs are 5 V parallel devices; expect many wires and larger PCBs. [“Graphic KS0108 LCD 128x64 + extras – Adafruit”]
- Many SPI 128×64 OLED/GLCD modules run at 3.3 V and need level shifting with 5 V Arduinos. [“2.7" Monochrome 128x64 OLED – Arduino Wiring & Test | Adafruit”]
What are the best free courses or tutorials to start LCD interfacing for my assistive head‑switch project?
Start with the resources shared in the thread: character/graphic LCD datasheets and step‑by‑step tutorials. They cover pinouts, timing, and example code—ideal for ramping up quickly before tackling UI. Work through these first, then refine your bill of materials and wiring. [Elektroda, Mark Harrington, post #21666959]
Should I pick a character LCD or a graphic LCD first?
Begin with a character LCD for status and prompts. Add an I2C/SPI backpack to reduce wiring, but note it won’t drive graphic LCDs. Move to graphic displays only if you need icons or scanning cursors. This staged approach keeps risk and wiring low early. [“I2C/SPI LCD Backpack | Adafruit Learning System”]
How many pins do I need to drive a 16×2 HD44780 in 4‑bit mode?
Six MCU pins: RS, EN, and D7–D4. Tie RW to ground for write‑only operation. “There is also a way to talk to the LCD using only 4 data pins instead of 8. This saves us 4 pins!” [“Wiring a Character LCD | Adafruit Learning System”]
Quick how‑to: How do I wire a 16×2 LCD in 4‑bit mode?
- Connect RS→MCU pin, EN→MCU pin, D7–D4→four MCU pins; tie RW to GND and V0 to a 10 kΩ contrast pot.
- Power VDD at 5 V, VSS to GND; backlight pins via resistor as specified.
- Initialize 4‑bit mode in code; then write commands/data as needed. [“Wiring a Character LCD | Adafruit Learning System”]
I’m using a 128×64 graphic display—what libraries should I look at?
For KS0108‑type 128×64 modules, use the GLCD or openGLCD libraries. They support pixels, lines, fonts, and bitmaps, simplifying UI prototyping for assistive devices. [“GLCD (ks0108) Graphic LCD Arduino Library, PJRC”]
What resolution do I get with 128×64, and why does it matter?
A 128×64 module provides 8,192 pixels. That’s enough for large arrows, scanning cursors, and clear head‑switch menus, even with high‑contrast themes. Use bitmap text or bold fonts for readability. [“128×64 Graphical LCD Display with u8glib library & Arduino”]
Can I power the backlight from a GPIO? How much current should I budget?
No. Many 16×2 backlights specify about 32–60 mA typical; power it from 5 V through a resistor or transistor, not a GPIO. Pulse‑width modulation gives dimming without glare for low‑vision users. [Crystalfontz CFah1602SYH datasheet page]
I’m on a 5 V Arduino but my SPI graphic/OLED runs at 3.3 V—what should I do?
Add level shifting for data/control lines and decouple the 3.3 V rail. Adafruit’s wiring guides show HC4050 level shifting and a bulk capacitor to stabilize 3.3 V during display refresh. [“2.7" Monochrome 128x64 OLED – Arduino Wiring & Test | Adafruit”]
The LCD looks blank—what’s a common failure I should check?
Mis‑set contrast (V0) can make a good display look dead. Adjust the contrast potentiometer; incorrect V0 often mimics a malfunction, especially in different temperatures. [“Hitachi HD44780 LCD controller – Wikipedia”]
Any thread‑specific advice on scope and difficulty for LCD work?
Yes: Expect a learning curve with command timing, 4‑bit/8‑bit modes, and scrolling. Plan time for drivers and interface choices (serial vs. parallel). Treat it like upper‑undergrad work and schedule accordingly. [Elektroda, Mark Harrington, post #21666948]
When should I pick the head‑tracking or gyro sensor?
Early. Your sensor choice affects pin count, power, and UI responsiveness, which feeds into the display choice and wiring plan. Share the exact part and datasheet to de‑risk integration. [Elektroda, Mark Harrington, post #21666957]
How do I reduce GPIO usage if my MCU is pin‑limited?
Use an I2C/SPI backpack on a character LCD to save four pins immediately, and keep only SDA/SCL or SPI lines for control. Move to graphic LCDs later if needed. [“I2C/SPI LCD Backpack | Adafruit Learning System”]
What’s the typical logic voltage/current for character LCDs?
Many HD44780‑compatible modules specify 5 V logic and around 1–1.5 mA logic current. Check your exact module’s datasheet and size the 5 V rail accordingly. [Crystalfontz CFah1602MY datasheet page]
Are there graphics libraries that abstract different displays?
Yes. Adafruit_GFX unifies drawing APIs across many TFT/LCD/OLED modules. It lets you port menus and icons between displays with minimal code changes. [“Using Adafruit GFX | 2.7" Monochrome 128x64 OLED”]
Does the I2C backpack work with 40×4 or graphic LCDs?
No. It supports standard HD44780 character LCDs and not 40×4 (dual‑enable) or graphic displays. Plan accordingly if you need graphics or large character matrices. [“I2C/SPI LCD Backpack | Adafruit Learning System”]
How does quadriplegia classification affect my UI design?
Design for head‑only input with clear visual feedback. The thread notes A–E categories of motor/sensory function; your user can move only the head and has intact cognition, guiding a simple scanning UI. [Elektroda, Mark Harrington, post #21666949]
