# Hardware

## Parts

- An ESP32-C6 dev board (e.g. ESP32-C6-DevKitC-1). Needs 8MB flash --
  see [`firmware/sdkconfig.defaults`](../firmware/sdkconfig.defaults) and
  [`firmware/partitions.csv`](../firmware/partitions.csv) if yours differs.
- [Waveshare 7.3" E Ink Spectra 6 (E6) panel](https://www.waveshare.com/7.3inch-e-paper-hat-e.htm) --
  800x480, 6-color, SPI.
- A USB cable for flashing/power.

## Wiring

The panel connects over SPI plus three control lines (data/command, reset,
busy). Defaults below match the reference build and are set in
[`firmware/components/epd7in3e/Kconfig`](../firmware/components/epd7in3e/Kconfig) --
override via `idf.py menuconfig` under **E-Paper Display (epd7in3e)
Configuration** if your wiring differs.

| Panel pin | ESP32-C6 GPIO | Kconfig option    |
| --------- | ------------- | ----------------- |
| CLK       | 20            | `EPD_PIN_CLK`      |
| DIN       | 19            | `EPD_PIN_MOSI`     |
| CS        | 18            | `EPD_PIN_CS`       |
| DC        | 9             | `EPD_PIN_DC`       |
| RST       | 10            | `EPD_PIN_RST`      |
| BUSY      | 11            | `EPD_PIN_BUSY`     |
| VCC       | 3.3V          | --                 |
| GND       | GND           | --                 |

Optionally, two buttons, both wired the same way -- momentary push button
between the GPIO and GND, no external resistor needed (the firmware
enables each pin's internal pull-up, so it idles high and reads low when
pressed):

- **Factory-reset (GPIO3)**: held for 10 seconds, clears the stored
  WiFi/server config; see
  [`firmware/README.md`](../firmware/README.md#resetting-to-provisioning-mode).
- **Next photo (GPIO2)**: a normal press skips immediately to the next
  photo; see
  [`firmware/README.md`](../firmware/README.md#skipping-to-the-next-photo).

Both pins were picked because they're within GPIO 0-7 -- the only pins
the ESP32-C6 can wake from deep sleep on -- aren't strapping pins, and
aren't already used by the panel wiring above.

A couple of things worth knowing if you pick different pins:

- **Avoid the ESP32-C6's strapping pins** (GPIO 4, 5, 8, 9, 15) and the
  USB-JTAG pins (12, 13) where possible -- strapping pins are sampled at
  reset to select boot mode. The reference wiring above already uses
  GPIO9 for DC, which *is* a strapping pin; it's only sampled during
  power-on/reset, so it's safe once the app is running, but if
  flashing/boot ever misbehaves on your board, check whether the panel is
  pulling that line low during reset.
- The panel's SPI interface is rated well above the firmware's default
  4MHz clock (`EPD_SPI_CLOCK_HZ`), but breadboard/dupont-wire connections
  are often unreliable much past a few MHz. Raise it once your physical
  wiring is confirmed solid.

## Power

The device spends nearly all its time in deep sleep, waking briefly once
an hour (configurable, see the server's web UI) to fetch and display a
photo. A full-color refresh on this panel takes 15-30+ seconds and draws
more current than deep sleep by a wide margin -- expect battery life (if
not running from USB power) to be dominated by refresh frequency, not
sleep current.