The Sleepy Pony AI08 Devboard Provides a Handy Platform for Capacitive Touch Sensor Experimentation

Programmer and electronics hobbyist Sirawit Lappisatepun has put together a development board designed to make it easier to get started with capacitive touch-sensing using the Xiamen Xinwang AI08 controller chip — called, imaginatively, the AI08 Devboard.

"Back in September 2022, I found a category on LCSC about capacitive touch controllers," Lappisatepun explains of the board's origin. "The touch controller chips come in all sizes (single input to many) and types (I2C, parallel output, etc.) and is a useful chip if you need to add touch support for your projects, so I want to try out one of them, the SAM&WING AI08."

The Xiamen Xinwang AI08 is an eight-channel capacitive touch controller, designed to work with just a handful of additional passive components. Its inputs are connected, with 1k Ohm series resistors, to buttons designed directly onto the PCB — boasting zero moving parts. As a finger touches the PCB "button," the controller senses the resulting change in resistance — and records it as a button press.

"To make things more useful, I decided to add some cheap logic chips to the board to decode the output further," Lappisatepun notes. "U5 is a 74HC138 decoder. The AI08 outputs conveniently allows us to just use this simple chip to decode the BCD [Binary Coded Decimal] output into parallel outputs for each channel. U3 is a 74HC11 triple 3-input AND gates and U4 is a 74AHC1G04 NOT gate. These two chips decode output 1011 and 1111 to create a 'no detection' and 'calibration' flags. The MSB [Most Significant Bit] of the BCD output is used to disable the 74HC138 decoder while either of the flags are active."

The development board created by Lappisatepun includes full support for the chip's automatic sleep and calibration modes, with the note that if the board is moved to a new location it should be powered on and allowed to sit "for at least a minute" before the capacitive sensors are touched. "The calibration seems to persist between power cycles," Lappisatepun adds, "so that's useful." When a sensor is touched, one of eight LEDs illuminate to indicate which channel it's on — while pin headers allow the signal to be sent to external hardware too.

More information on the board is available on Lappisatepun's website, while the design files can be found on GitHub under the permissive Solderpad Hardware License v2.1.