Capacitive Touch Sensor

Wrote by  Jiang Hao.

In electrical engineering, capacitive sensing is a technology based on capacitive coupling which takes human body capacitance as input.

Capacitive sensing is used in many different types of sensors, including those to detect and measure proximity, position or displacement, humidity, fluid level, and acceleration. Capacitive sensing as a human interface device(HID) technology,  for example to replace the computer mouse, is becoming increasingly popular.

Capacitive touch sensors are used in many devices such as laptop trackpads, digital audio players, computer displays, mobile phones, mobile devices, tablets and others. They are constructed from many different media, such as copper, Indium tin oxide (ITO) and printed ink. All the three sensors that would be introduced below  belong to the first. Copper capacitive sensors can be implemented on standard FR4 PCBs as well as on flexible material.

There are two types of capacitive sensing system and the sensors use mutual capacitance, where the object (finger, conductive stylus) alters the mutual coupling between row and column electrodes, which are scanned sequentially. In both cases, the difference of a preceding absolute position from the present absolute position yields the relative motion of the object or finger during that time.

More and more design engineers are selecting capacitive sensors for their versatility, reliability and robustness, unique human-device interface and cost reduction over mechanical switches. However we don’t have many capacitive sensors on the market for us to make what we want ourselves.

Now, we have 3 good choice!

1. Capacitive Touch Sensor 

This sensor can sense the human body and metal, when they touch the sensor. In addition to this, the detection works even when separated by plastic, glass and other materials. In combination with arduino boards, the sensors can be used to create very interesting and interactive projects.

This is a light guitar and it has some lights controlled by the touch sensor.

Sample code can be found in wiki.

2. Mini Touch kit 

It includes a metallic tape with a sticky side. This makes it possible for you to place your sensors anywhere you want. So, if you get sick of the typical push buttons, try this invisible button for your projects! This touch sensor works on a variety of surfaces; Metal, glass, plastic, rubber. It does not work on cardboard or wood.

This is a funny angry bird with a mini touch fixed on it’s tail. If you touch the tail, the eyes will be lighted.
About the connection of mini touch kit, you can check this video, and the sample code in the wiki.

3. Capacitive Touch Kit

An ipod styple wheel touch, a keypad touch which supports backlit and a grid touch pad which can recoginze something unique.This kit utilizes the not very "latest" capactive touch technology which make the sensing very sensitive.
 

The kit is designed to be compatible with Arduino.

The keypad shows numbers such as the dialer on our mobile photo. The wheelpad is the same as the wheel used on ipod, so we can use it to control something, for example, to adjust the brightness of a light.

Here is a project which uses the keypad to control the color of light. Each point on the keypad stands for a different color. Also we can use wheelpad or touchpad to realize the function.