+---------------------------------------------------------------------------------------+
|  ESP32-DevKitC-V4  ---  flow-meter                                                    |
+---------------------------------------------------------------------------------------+
|  Rails: 5V, 3V3, GND                                                                  |
|                                                                                       |
|  flow  [Pulse counter / tachometer (RPM, flow, energy)]  -- Flow                      |
|    PULSE -> GPIO4                                                                     |
|                                                                                       |
|  strip  [APA102 / SK9822 addressable RGB LED strip (SPI / DotStar)]  -- Status strip  |
|    VCC   -> rail 5V                                                                   |
|    GND   -> rail GND                                                                  |
|    DI    -> GPIO23                                                                    |
|    CI    -> GPIO18                                                                    |
|                                                                                       |
|  buzzer  [Piezo buzzer + RTTTL melody player]  -- Buzzer                              |
|    OUT   -> GPIO19                                                                    |
|    GND   -> rail GND                                                                  |
|                                                                                       |
|  BOM:                                                                                 |
|    - ESP32-DevKitC-V4                                                                 |
|    - Pulse counter / tachometer (RPM, flow, energy)  (flow)                           |
|    - APA102 / SK9822 addressable RGB LED strip (SPI / DotStar)  (strip)               |
|    - Piezo buzzer + RTTTL melody player  (buzzer)                                     |
|                                                                                       |
|  Power: ~38mA typical, ~90mA peak (budget 500mA)  OK                                  |
|                                                                                       |
|  Warnings: none                                                                       |
+---------------------------------------------------------------------------------------+
