Customer:
After about 15 months, my Inkplate’s time-triggered wakeup stopped working when powered by battery, though it works fine on USB power. I’ve tried two Li-Ion batteries (3.7V 1200mAh) both individually and in parallel, fully charged each time. The batteries appear to supply sufficient current for startup. This is a basic functionality that worked for over a year and has now stopped.
Originally submitted via email support on 30 December 2021. Migrated to the forum for community visibility.
Soldered Support:
Wakeup should work on battery power. The most likely issue would be insufficient current from a discharged battery, but that doesn’t apply here since you’re using fully charged batteries. Are you using the same hardware (Inkplate and battery) as you were when it last worked, or has something changed? Can you try another example on the Inkplate and check if it refreshes or has problems when powered by battery?
Customer:
Nothing has changed. The Inkplate was running with the same software, linked to the same WiFi network, and recharged every 3 to 4 weeks. After the last recharge, both timer-based wakeup and touchpad-based wakeup suddenly stopped working on battery power alone. Everything works fine with a power supply connected, but that defeats the purpose of having a wall-mounted Inkplate. This looks like a partial hardware failure.
Soldered Support:
It’s unusual that the Inkplate only wakes up on USB power, since the ESP32 operates on 3V3 which is provided through a voltage regulator. The same voltage regulator supplies 3V3 whether the board is powered by battery or USB. Can you measure the voltage on the 3V3 pin when powered by USB and when powered by battery? Also, can you share the code you’re using so I can test it on my Inkplate?
Customer:
Even though the problems occurred without any trigger, I updated to Inkplate library version 5.5.1 and Inkplate Boards version 1.0.1. I installed the Inkplate_Wake_Up_On_Touchpad example from the library.
When connected via USB (with battery also present), everything works fine. The board starts up, sleeps for 30 seconds, reboots, and responds to touchpad presses.
After disconnecting the USB cable, the board hangs with no timer wakeups. Pressing the reset button puts the Inkplate into an endless loop, rebooting every 2-3 seconds with the output: “Boot count: 1 Wakeup was not caused by deep sleep”
After reconnecting USB, the board hangs again and only recovers after pressing reset.
This behavior matches Unexpected behavior under battery only · Issue #56 · SolderedElectronics/Inkplate-Arduino-library · GitHub
My board is an older one. I had previous trouble with the panel and the battery ADC: Determining battery voltage unreliable · Issue #36 · SolderedElectronics/Inkplate-Arduino-library · GitHub
Battery voltage during testing was 4.17V.
Attachment omitted in migration: Weitergeleitete Nachricht
Soldered Support:
Which Inkplate board do you have (Inkplate 6 or Inkplate 10)? If you have an Inkplate 6, you have the capacitor problem described at Unexpected behavior under battery only · Issue #56 · SolderedElectronics/Inkplate-Arduino-library · GitHub. If you have a soldering iron, replace this capacitor. The battery voltage causes the ESP32 to reset because the voltage on the RESET pin is too low. USB voltage is higher, which is why everything works there.
Customer:
I have an Inkplate 6 (first version). What kind of capacitor should I use for this repair? Tantalum, ceramic, or something else? Should I add a 2uF capacitor in addition to the existing one, or replace it? What is the capacitor currently on the board?
Soldered Support:
You can use a ceramic capacitor with a value around 2.2uF or higher. You can also solder an additional 2.2uF capacitor in parallel with the existing capacitor on the board, which is easier since you don’t need to remove the old one. If you have the first version of Inkplate 6, there’s a 100nF capacitor in that location. If you have problems after soldering, feel free to contact us.