3x3 capacitive touchpad

Introduction

I bought a Chinese 3x3 capacitive sensor touch-shield for on the Arduino (Uno, Mega, Due), but could not find any library that worked with it. Investigating the main chip it shows not the standard chip supported by the Arduino libraries, but an unbranded chip.

The text found on different sides is:

"IC is a way to establish a simple capacitive touch interfaces. Now, by touching the shield, to establish a connection with your Arduin project is even more simple. The shield has nine capacitive touch touch pad. These touch pads are left with three electrode connection point of the joint. With this board, you can get a total of 12 touch-sensitive buttons. An on-board logic level to work with 5V or 3.3V allows the Ardu ino board. Some simple solder pin connector. Stack your Ardui no to get a better input devices. Provides sample code."

So that description is not helping.

Overview

Button-side:

Component side:

And a closer look to the main-IC:

It is asif the identification is burned off.

Circuit

The main component on the board is a TQFP-32 IC, which has no identification (and the supplier from AliExpress also does not want to tell me).

So following the connections on the board I retrieve the following circuit (components placed according the component-side-view).

Based on the above circuit I checked possible TQFP32 chips but none of the pinning matched the circuit above.

Compared the following datasheets: QT60168-ASG, AT42QT2100, AT42QT1110, QT60248C-ASG, AT42QT1244, AT42QT1245, QT60160, QT60240, (TSM12), (TS20), (TTP229).

 Arduino code

As is clear from the above circuit, without knowning what the IC is, it will be hard to write code based on the above circuit.

What is clear from the circuit is:

• It uses I2C communication (SDA and SCL are connected on the Arduino pins)
• It is missing the I2C pull up resistors. So before trying the code add to both SDA and SCL a 4.7kOhm connection to +5V.
• It is connected to the digital pins 8,9,10,11,12 and analog A0.

Tests applied:

• Via a I2C sniffer the address of the device is determined
• Followed by a scan through all possible registers
• Followed by changing pins D8, D9, D10, D11, D12, A0 as output (and with values 0, 1) => but there was no different read-out found
• Followed by changing pins D8, D9, D10, D11, D12, A0 as inputs => but there was no read-out found on these pins when buttons were pressed

Conclusions:

• I2C device with address 0x28
• Registers can be readout which change value when key is touched
• Extra Arduino connections
  • I was expecting that the D8, D9, D10, D11, D12, A0 were used either as:
    • Address setting
    • Connection to the other 3 keypads (the description mentions 12 capacitive buttons)
      • but in that case a R, C network should be added (untested)
    • Trigger when any key is touched
  • None of the inputs were responsive

Arduino code

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