An ESP32-based e-paper display that shows today's Octopus Energy Agile electricity prices as a bar chart. The device wakes from deep sleep every 15 minutes to update the display, fetching fresh price data from the Octopus Energy API every 6 hours.

![Display showing a day of Agile electricity prices as a bar chart with cheap slots shown as white bars and expensive slots as black bars]

• Full-day bar chart of 30-minute Agile tariff price slots
• Bars above the median price filled black (expensive), below shown as white outlines (cheap)
• Current time slot highlighted with a vertical line
• Extremely low power consumption — WiFi and display are off most of the time
• RTC drift compensation — measures and corrects ESP32 clock drift between NTP syncs

• PlatformIO (CLI or VSCode extension)
• Octopus Energy account on the Agile tariff

Copy the credentials template and fill in your details:

cp src/credentials.h.example src/credentials.h

Edit src/credentials.h:

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";

#define OCTOPUS_PRODUCT_CODE "AGILE-24-10-01"  // Check Octopus API for current product code
#define OCTOPUS_REGION_CODE "E"                 // Your region — see below

Region codes: A=Eastern, B=East Midlands, C=London, D=Merseyside & N Wales, E=West Midlands, F=North East, G=North Scotland, H=North West, J=South East, K=South Scotland, L=South Wales, M=South West, N=Southern, P=Yorkshire.

The current Agile product code can be found via the Octopus Energy API docs.

# Build and upload
pio run -t upload

# Monitor serial output (useful for debugging)
pio device monitor

# Build the debug variant (shows current time on screen)
pio run -e debug -t upload

The device spends almost all its time in deep sleep. On each wake (every 15 minutes, aligned to clock boundaries):

1. Checks if WiFi is needed — required for first boot, every 6 hours for price data, or if the clock isn't set
2. Syncs time — via NTP (pool.ntp.org), falling back to the WorldTimeAPI HTTP endpoint
3. Fetches prices — from api.octopus.energy if the 6-hour interval has elapsed
4. Updates the display — only if the current 30-minute rate slot has changed, new data arrived, or ~1 hour has passed (periodic anti-ghosting refresh)
5. Sleeps — until the next 15-minute boundary

Price data and RTC state are stored in ESP32 RTC memory, which survives deep sleep.

• GxEPD2 — e-paper display driver
• Adafruit GFX — graphics primitives
• ArduinoJson — JSON parsing

The project includes a custom e-paper driver (lib/GxEPD2_290_Custom/) that fixes a busy-wait timeout issue specific to this display hardware by changing a single update command byte (0xc7 → 0xc4).