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First Power-On Checklist

Before writing the full firmware, verify each component is wired correctly using simple test sketches. Work through this list in order — each step confirms one subsystem before you build on it.

Visual Inspection (Do This Before Every Power-On)​

  • No bare wire ends touching adjacent pins or exposed metal
  • VCC wires connected to the correct voltage rail (3.3 V or 5 V)
  • GND wires connected (every component needs GND)
  • No component is mounted backwards (check any IC with a direction marker)
  • LittleFS partition image has been flashed (no physical SD card needed)

Step 1: ESP32 Standalone​

Connect only the ESP32 to USB. Confirm the serial monitor outputs something and the blink example works. No other components connected.

Expected: LED blinks, serial prints Turning on LED / Turning off LED.

Step 2: DS3231 RTC​

Wire the DS3231 (VCC, GND, SDA, SCL). Run the I2C scanner.

Expected:

Found device at 0x68

If nothing appears: measure VCC with a multimeter (should read ~3.3 V). Confirm SDA → GPIO21 and SCL → GPIO18. Check that pull-up resistors are on the breakout board.

Step 3: Buttons​

Wire all 6 buttons (one pin to GPIO, other pin to GND). Run the polling test from the buttons wiring doc.

Expected: pressing each button prints its name.

If a button does not respond: check that both terminals of the button are wired (one to GPIO, one to GND). Measure GPIO voltage with a multimeter — should be ~3.3 V when not pressed and ~0 V when pressed.

Step 4: LittleFS Flash Partition​

Flash the LittleFS image with esptool.py write_flash (see the Audio Storage page). Call lfs_init() and verify alarm.wav is accessible.

Expected: I (xxx) lfs: alarm.wav found, size N bytes in serial output.

If mount fails: confirm the lfs partition label matches the driver config. Confirm the image was flashed to the correct offset from partitions.csv.

Step 5: E-ink Display​

Wire the display adapter (VCC, GND, MOSI, MISO, SCLK, CS, DC, RST, BUSY, FL_PWM). Run the RST + BUSY check from the display wiring doc.

Expected: Display ready printed to serial. Display shows a full white refresh.

If BUSY never goes LOW: check RST is connected to GPIO4. Check BUSY is connected to GPIO3. Verify VCC on the adapter board.

Step 6: MAX98357A + Speaker​

Wire the amp (VIN=5V, GND, BCLK, LRCLK, DIN). Ensure alarm.wav is in the LittleFS partition at /lfs/alarms/alarm.wav. Run the audio playback test from the audio wiring doc.

Expected: alarm audio plays from the speaker.

If silent: check DIN → GPIO17 (not DOUT). Verify VIN is 5 V, not 3.3 V.

All Systems Go​

If all six steps pass, every component is wired and communicating correctly. Proceed to the Firmware section to build the full application.

Moving to Perfboard​

Once the breadboard prototype is working:

  1. Sketch the component layout — keep the display adapter close to the display ribbon cable; keep the amp close to the speaker terminals
  2. Solder components one at a time, re-testing at each step
  3. Use stranded silicone wire for speaker connections (it handles vibration better than solid-core wire)
  4. Apply a small amount of hot glue or strain relief to the display ribbon cable where it meets the adapter — the FPC connector is fragile and can crack with repeated bending