RITHESH LED Display

@@ -0,0 +1,84 @@+# Requirements++This file lists what the board needs to do. Items marked **TBD** (to be decided)+still need an answer before the PCB design starts.++## Must have++1. Display the word "RITHESH" (7 letters) using WS2812B RGB LEDs.+2. Control the LEDs over Wi-Fi.+3. Be powered from a USB-C phone charger (5 V).++## Decisions made++| Decision | Choice | Notes |+|----------|--------|-------|+| Board size | About 300 x 70 mm | "Large" option. |+| Letter pattern | 5 x 7 grid per letter (5 columns wide, 7 rows tall) | Only the grid spots that form the letter get an LED. Patterns below. |+| LED spacing | 7 mm, center to center | Same spacing across and down. |+| LED type | WS2812B (5 x 5 mm package) | Big enough to hand-solder. |+| Total LEDs | **107** | Counted from the letter patterns below (earlier estimate was 110). |+| Power input | USB-C, 5 V, up to 3 A | Simplest option for a first board. |+| LED power limit | **2,000 mA** (2 A) for all LEDs together | Set in the firmware. See "Power budget" below. |++### Letter patterns (● = LED, · = empty)++```+  R        I        T        H        E        S        H+●●●●·    ·●●●·    ●●●●●    ●···●    ●●●●●    ·●●●●    ●···●+●···●    ··●··    ··●··    ●···●    ●····    ●····    ●···●+●···●    ··●··    ··●··    ●···●    ●····    ●····    ●···●+●●●●·    ··●··    ··●··    ●●●●●    ●●●●·    ·●●●·    ●●●●●+●·●··    ··●··    ··●··    ●···●    ●····    ····●    ●···●+●··●·    ··●··    ··●··    ●···●    ●····    ····●    ●···●+●···●    ·●●●·    ··●··    ●···●    ●●●●●    ●●●●·    ●···●+ 18       11       11       17       18       15       17     = 107+```++### Quick size check++- One letter: 5 columns -> 4 gaps x 7 mm = 28 mm, plus 5 mm for the LED = about 33 mm wide.+  7 rows -> 6 gaps x 7 mm = 42 mm, plus 5 mm = about 47 mm tall.+- Whole word: if we leave one empty column between letters, that is+  7 x 5 + 6 = 41 columns -> 40 gaps x 7 mm + 5 mm = about **285 mm wide**.+  This fits in 300 mm with about 7 mm of margin on each side.+- Height: letters take about 47 mm of the 70 mm, which leaves about 23 mm for+  the Wi-Fi chip, power parts, and connectors. It will be a tight fit, so some+  parts may go on the back of the board.++## Power budget++The charger gives at most 3 A. We split it like this:++| Where the power goes | Current |+|----------------------|---------|+| Safety margin (so the charger never runs at its limit) | 0.5 A |+| ESP32 chip and its voltage regulator (Wi-Fi bursts up to about 0.35 A) | 0.5 A |+| All LEDs together, including the ~1 mA each LED uses even when off | **2.0 A** |+| **Total** | **3.0 A** |++What 2.0 A means in practice:++- Every LED at full white would need about 107 x 60 mA = 6.4 A.+  2.0 A is about **30%** of that, so all-white is limited to about 30% brightness.+- One color at a time uses much less (about 20 mA per LED at full brightness),+  so pure red, green, or blue can run at about 90% brightness.+- The firmware applies the limit automatically: it dims everything just enough+  to stay under 2.0 A, and leaves dimmer patterns alone.++## Charger and USB-C rules++- Use a USB-C charger labeled **"5V ⎓ 3A"**, or a USB-C Power Delivery (PD)+  charger rated **15 W or more**, with a **USB-C to USB-C** cable.+- Not every charger qualifies. Older or small chargers, laptop USB ports, and+  USB-A to USB-C cables may give only 0.5 to 1.5 A.+- The board must have two **5.1 kΩ resistors** on the USB-C "CC" pins.+  Without them, a USB-C charger will not turn on its 5 V output at all.++## Open questions (TBD)++| Question | Why it matters | Answer |+|----------|----------------|--------|+| Which Wi-Fi chip? (e.g. ESP32-C3 module) | Affects cost, size, and how easy it is to program. | TBD |+| Hand-soldered or factory-assembled? | Changes which part sizes are practical. | TBD |+| Detect weaker chargers automatically? | The ESP32 can read the CC pins to see whether a charger offers 3 A, 1.5 A, or less, and lower the LED limit to match. Optional, but safer. | TBD |