Creative Inspiration Center Micro:Bit Basic Programming Guide Input Function Group (Special Analysis)2
IICapacitive touch button principle
Capacitive touch keys, also known as touchless touch key switches. We.
An independent capacitive touch button switch module is taken as an example to illustrate the working principle of capacitive touch buttons.
Touch sensors have been widely used for many years. The development of mixed-signal programmable devices has made capacitive touch sensors a practical, value-added alternative to mechanical switches in a variety of consumer electronics.
For typical capacitive sensors, a thickness of 3 mm or less is specified. As the thickness of the overlay increases, it will become more and more difficult to touch with your fingers. In other words, as the thickness of the overburden increases, the system adjustment process will have to leapfrog from "science" to "excellence".
Finger capacitance. At the heart of any capacitive touch sensing system is a set of conductors that interact with an electric field. Underneath, human tissue is filled with conductive electrolytes (a lossy dielectric). It is this conductive property of the finger that makes capacitive touch sensing possible.
A simple parallel plate capacitor has two conductors separated by a layer of dielectric. Most of the energy in this system stays directly between the capacitor plates. A small amount of energy leaks into the space outside the capacitor plates, and the electric field formed by this leaked energy is called the "edge field". Part of the challenge in making a practical capacitive sensor is that it is necessary to design a set of printed wires that direct the aforementioned edge field into an effective sensing area that is easily accessible to the user. Obviously, mezzanine plate capacitors are not the best choice for this sensor mode.
Placing your finger near the edge of the electric field will increase the conductive surface area of the capacitive sensing system. The additional charge storage capacity generated by the finger is known as the finger capacitance cf. The capacitance of the sensor when touched without fingers is expressed in cp. In this article, it stands for parasitic capacitance.
A common misconception about capacitive sensors is that in order for the system to work properly, the finger must be grounded. In fact, the reason the finger is sensed is that it has an electric charge, which has nothing to do with whether it is suspended or grounded.
Introduction to capacitive touch modules
1. Working voltage: DC 3-5V
2. Main components: op amp, transistor.
3. Size: length 45mm x width 18mm x height 5mm
Under normal conditions, the output of the module is low, and the mode is low-power modeWhen touching the corresponding position with your finger, the module will output a high level and the mode will be switched to fast modeWhen there is no touch for 12 seconds, the mode switches to low-power mode again. The module can be installed on the surface of non-metallic materials such as plastic and glass, and a thin piece of paper (non-metal) can be covered on the surface of the module, and as long as the position is correct, it can be made into a button hidden on the wall, desktop, etc. This module allows you to eliminate the hassle of regular push-type keys.
Module Features::
1. Jogging type: the initial state is low, the touch is high, and the non-touch is low-level (similar to the function of touching the button).
2. Low power consumption.
3. The power supply can be 2 55v dc
4. The front and back sides can be used as touch surfaces, which can replace the traditional light touch buttons.
M2 screw positioning holes for easy installation.
Working Mode Description:
By touching the touch-type touch sensor and then holding the touch-sensor for a long time, the normal high-level output at the SIG signal end or the high-level and low-level switching output of the intermittent signal in the pulse state can be realized.
Control Interface:
There are 3 pins (GND, VCC, SIG), GND is ground, VCC is the power supply, and SIG is the digital signal output pin
Power Indicator:
Green LED, glows when powered on correctly;
Touch area:
The fingerprint-like inner area of the icon can be triggered by a light touch of the finger.
Locating holes:
4 m2 screw positioning holes with a hole diameter of 22mm, so that the module is easy to install and position, and realize the combination between modules.