CodeCell - Going to Sleep

CodeCell supports low-power sleep using either a periodic RTC timer or sensor-driven interrupts. Each method has different power characteristics, so choosing the right wake strategy is essential for low-power applications.

Sleep Current by Board & Wake Source

All official sleep examples are in the repo: examples/Sleep

RTC Timer vs Interrupt Wakeup - What’s the Difference?

CodeCell offers two different wakeup strategies, each for different power-use applications.

🔹 RTC Timer Wakeup (Lowest Power)

The device sleeps in deep-sleep mode and wakes periodically based on an RTC timer. While asleep, current is constant (≈ 40 µA on C6 / C6 Drive).

On each wake cycle, the firmware must:

• Re-initialize the sensors
• Check if the sensor condition was triggered
• Return to sleep if nothing happened

Because the ESP32 is in deep-sleep and the sensors are fully off between timer events, this mode saves the most energy.

The longer the timer interval → the more time spent in deep sleep → the lower the average current.

But, long intervals increase response delay (e.g., motion change might only be detected instantly). The graph below shows how RTC sleep behaves: the device spends around 1 second in deep sleep and only wakes periodically to check the sensor readings.

On this graph:

• The long flat sections show deep sleep (~40 µA).
• The tall spikes represent wake cycles where the device re-initializes sensors.
• Increasing the timer interval makes the sleep sections longer → reducing average energy use.

🔹 Sensor Interrupt Wakeup (More Reactive, Higher Current)

Sensors can stay partially powered to wake the ESP32 instantly on events like tap, proximity, or light changes. But part of their circuitry needs to remain active, so sleep current is higher.

• Tap interrupt (BNO085): ≈ 860 µA (C6) · ≈ 1730 µA (C6 Drive)
• Brightness interrupt (VCNL4040): ≈ 280 µA (C6 / C6 Drive)
• Proximity interrupt (VCNL4040): ≈ 425 µA (C6 / C6 Drive)

This mode provides instantaneous wakeups, ideal for user interactions or immediate alarms at the cost of constant current draw.

Sleep Examples (Quick Navigator)

• 1) Tap Interrupt Wakeup — C6 / C6 Drive
  Sleep on command; wake instantly on tap.
  tap_interrupt_wakeup.ino
  Est. sleep ≈ 860 µA (C6) · 1730 µA (C6 Drive)
• 2) Brightness Interrupt Wakeup — C6 / C6 Drive
  Wake when light rises above a threshold.
  brightness_interrupt_wakeup.ino
  Est. sleep ≈ 280 µA (C6 / C6 Drive)
• 3) Proximity + Timer + EEPROM Wakeup — C3 / C3 Light / C6 / C6 Drive
  Timed sleep with proximity re-check on wake.
  proximity_timer_eep_wakeup.ino
  Est. sleep ≈ 40 µA (C6) · 476 µA (C3 Light) · 861 µA (C3)
• 4) Darkness Interrupt Wakeup — C6 / C6 Drive
  Wake when light falls below a threshold.
  darkness_interrupt_wakeup.ino
  Est. sleep ≈ 280 µA
• 5) Motion (RTC Timer Poll) Wakeup — C3 / C3 Light / C6 / C6 Drive
  Lowest-power motion detection using periodic RTC wake.
  motion_timer_wakeup (folder)
  Est. sleep ≈ 40 µA (C6) · 861 µA (C3)
• 6) Proximity Interrupt Wakeup — C6 / C6 Drive
  Instant wake when proximity crosses a threshold.
  proximity_interrupt_wakeup.ino
  Est. sleep ≈ 425 µA

Choosing a Strategy

• Best battery life: Use RTC timer sleep (~40 µA on C6 / C6 Drive).
• Instant reaction: Use interrupt-based wake (tap / proximity / brightness).