espresso_frame/docs/hardware.md

Hardware

Parts

• An ESP32-C6 dev board (e.g. ESP32-C6-DevKitC-1). Needs 8MB flash -- see firmware/sdkconfig.defaults and firmware/partitions.csv if yours differs.
• Waveshare 7.3" E Ink Spectra 6 (E6) panel -- 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 -- 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, three buttons, all 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):

• Next photo (GPIO2): a normal press skips immediately to the next photo; see firmware/README.md.
• Back photo (GPIO0): a normal press returns to the previously-shown photo; see firmware/README.md.
• Menu / reset (GPIO1): one button, three actions by hold duration -- a quick press soft-resets the device (config kept); holding ~3s then releasing overlays a "scan to manage" QR code on the current photo for 30 seconds; holding ~15s factory-resets it (clears WiFi/server config, reprovisions); see firmware/README.md.

All three 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. Also, not incidentally, GPIO 0-7 is all the deep-sleep-wakeup-capable pins this chip has (SOC_RTCIO_PIN_COUNT is 8) -- worth knowing if you're targeting a compact board like the Seeed XIAO ESP32-C6, which only breaks out 3 of them (GPIO0/1/2). These three buttons were deliberately designed to fit exactly that budget: two dedicated pins for the actions where instant, unambiguous response matters most (next, back), and everything else folded onto the third pin via hold duration instead of needing its own pin.

Wiring on the Seeed XIAO ESP32-C6

The XIAO only breaks out 11 GPIOs (0, 1, 2, 16, 17, 18, 19, 20, 21, 22, 23), so the dev-board defaults above don't fit -- DC/RST/BUSY (GPIO 9, 10, 11) aren't exposed on this board at all. Built with build_for_board.sh xiao, which layers firmware/sdkconfig.xiao on top of the dev-board defaults, remapping DC/RST/BUSY onto three of the remaining free pins:

Panel pin	XIAO GPIO	XIAO silkscreen label	Kconfig option
CLK	20	D9	EPD_PIN_CLK (unchanged)
DIN	19	D8	EPD_PIN_MOSI (unchanged)
CS	18	D10	EPD_PIN_CS (unchanged)
DC	16	D6	EPD_PIN_DC
RST	17	D7	EPD_PIN_RST
BUSY	21	D3	EPD_PIN_BUSY
VCC	3.3V	3V3	--
GND	GND	GND	--

The XIAO's silkscreen labels its pins D0-D10, not raw GPIO numbers -- the table above gives both.

Buttons (unchanged from the table above -- the XIAO's only three ADC/deep-sleep-capable pins, GPIO 0/1/2, are exactly the ones already used): next=GPIO2/D2, back=GPIO0/D0, menu/reset=GPIO1/D1. That leaves GPIO22/D4 and GPIO23/D5 free, e.g. for the optional VBUS mains-sense divider described under Battery below.

sdkconfig.xiao also sets FRAME_XIAO_ANTENNA_INIT=y, which powers the XIAO's onboard RF switch and selects its ceramic antenna at boot (GPIO3/14, internal to the board -- not part of the wiring above). Without it, WiFi doesn't reliably work on this board at all: the radio comes up and logs look normal (e.g. the softAP starts and prints its SSID/password) but the switch's control pins are left floating, so nothing actually reaches the antenna -- the AP never becomes visible to a scan, and a station connection would fail to associate the same way. Seeed's own Arduino board package does this automatically; plain ESP-IDF (what this firmware uses) doesn't, hence the explicit init.

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.

Battery (optional, XIAO ESP32-C6)

For a battery-powered build on the Seeed XIAO ESP32-C6 (which has BAT+/BAT- charge pads on its underside and charges over USB-C):

• A 1S 3.7V LiPo with an integrated protection circuit (the board does no low-voltage cutoff of its own), soldered or JST-PH-pigtailed to the BAT pads. JST-PH polarity is not standardized -- verify with a multimeter before connecting.
• Battery level sense: two equal-value resistors in series from BAT+ to GND (200k is the reference value, but any matched pair works -- it's a ratio divider, so what matters is the two resistors matching each other, not the absolute value; higher values just draw less constant current from the battery, e.g. ~10uA for 200k+200k vs ~2uA for 1M+1M, at the cost of a slightly noisier ADC reading from the higher source impedance -- not noticeable in practice up to around 1M given how coarse the percent curve already is). Midpoint to GPIO0/A0 (shared with the back button -- deliberate, see firmware/README.md).
• Optional mains detection: 2x100k divider from the 5V pin to GND, midpoint to a spare GPIO (e.g. 22).

Both features are off by default in firmware (FRAME_BATTERY_ADC_GPIO/FRAME_VBUS_SENSE_GPIO = -1) -- except FRAME_BATTERY_ADC_GPIO, which firmware/sdkconfig.xiao turns on (GPIO0) by default for XIAO builds, since that's the one board this feature was designed for. Mains detection stays off by default even there; set FRAME_VBUS_SENSE_GPIO yourself if you wire that divider too.

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.