AT42QT101X Capacitive Touch Breakout Hookup Guide

Contributors: Elias The Sparkiest, Shawn Hymel
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Hardware Overview

If we look at the front of the board, we see a large, circular pad (the "electrode") and several pins. The on-board electrode will detect touches when pressed with a finger as long as the board is powered.

Front of PCB

AT42QT101X Breakout front

GND should be connected to the ground of the host circuit.

GROUND PTH of Capacitive Touch

OUT is the output of the AT42QT101X. HIGH on touch, LOW otherwise.

OUT PTH of Capacitive Touch

VDD is the power supply for the AT42QT101X and needs to be connected to a voltage between 1.8V - 5V.

VDD PTH of Capacitive Touch

LED controls the operation of the on-board LED. By default, it is connected to the OUT pin. If you de-solder the "LED Enable" jumper on the back side, you can independently control the LED.

LED PTH of Capacitive Touch

PAD is located in the upper-left corner and allows you to connect to an external electrode. Note that there is a small surface mount pad on the back side by the PAD pin hole. If you want to mount the board flush, you can solder a wire directly to the surface mount pad.

PAD PTH of Capacitive Touch

How It Works

Take a look at the back side of the AT42QT101X. Both versions share the exact same PCB layout but different IC's (lower right "1011").

Backside of the 1011

AT42QT1011 Breakout Back

The AT42QT101X chip is located on the right side of the board. It uses a resistor and a capacitor network to adjust the sensitivity of the electrode. High frequency pulses are sent to the pad. When a fleshy object (such as a finger) approaches the pad, it acts like a very small capacitor and changes the shape of the pulses. When the AT42QT101X detects these slight changes, it raises the OUT line to HIGH, indicating a touch is present. The duration of the output depends on the chip that is populated. Once the pulses return to normal, the AT42QT101X drives the OUT line LOW.

AT42QT1010 vs AT42QT1011

The version of your chip is indicated by the small check boxes on the back side. We offer two versions of the same chip: the AT42QT1010 and the AT42QT1011. Both boards function the same with one small caveat: the AT42QT1010 has an internal timeout of ~60 seconds where as the AT42QT1011 does not. Meaning that if you hold your finger to the AT42QT1010's pad for more than 60 seconds than the boards' OUT pin will go low (turn itself off). The difference is small but may be a game changer depending on your project's uses.

Note: Depending on your power supply, the AT42QT-1011 IC may not stay on indefinitely when powering your microcontroller with less reliable wall warts. If your sensor is not operating as expected, try powering your microcontroller through your computer's USB ports or other more steady power supplies.

LED Enable

The output from the AT42QT101X goes directly to the OUT pin on the board as well as to the transistor (left side), which operates the LED (center of board). By default, the OUT line and LED lines are connected, which means that on a touch, the on-board LED lights up. You can disconnect the LED by de-soldering the jumper labeled "LED Enable." This will cause the LED to no longer light up on a touch, but you can still drive the LED using the LED pin on the board.


On the right side of the board, you will also notice a jumper labeled "Mode" with "1" and "2" markers. By default, the center pad and the "1" pad are connected, which puts the AT42QT101X in "Fast" mode. In Fast mode, the chip is more responsive to touch events but draws 200µA - 750µA in normal operation. If you de-solder this jumper and connect the center pad to the "2" pad, the AT42QT101X will be in "Low Power" mode. In this mode, the chip is slightly less responsive to events but only uses 15µA - 75µA. Keep in mind that the current draw of the IC itself. The LED draws another 30-40mA but can be disabled by removing solder from the "LED enable" solder jumper.