2025-11-08 ChLCD e-paper like displays in cheap drawing/writing boards
From Wikistix
Advertised as LCD drawing boards or LCD writing boards, writing tablets, etc. They don't use typical LCD screens, they don't have pixels, and they don't need a computer to drive the screen. They use pressure from a stylus to make persistent marks on the screen, and a button to erase. Most seem to be powered by a 3V coin cell battery, which is only used to erase when the button is pressed.
The name of the technology appears to be "cholesteric liquid crystal display" (ChLCD). Wikipedia has a deep technical page on cholesteric liquid crystals.
The erase operation delivers a surprising voltage (~65V here, for ~200ms) across conductive layers in the display, which I captured on my oscilloscope:
ChLCD erase operation oscilloscope trace
