Capacitive touch sensors are based on the electrical capacitance of the human body. When, for example, a finger comes close to the sensor, it creates a capacitance to Earth with a value of 30 to 100 pF. This effect can be used for proximity detection and touch-controlled switching. Capacitive switches have clear advantages compared to other types
Click here to download the full size of the above Circuit.
of touch switches (for example 50 Hz or 60 Hz detection or resistance detection), but are often more complex to implement. Manufacturers such as Microchip have in the past designed specialist ICs for this purpose. However, it is still possible to design a reliable capacitive detector and/or switch using only a limited number of standard components. In this design we detect the change in the pulsewidth of the signal when the contact is touched. In Figure 1 the following stages can be recognised, from left to right:- a square-wave generator with a frequency of 300 kHz, using a Schmitt trigger IC (CD4093); - an RC network with a fly-back diode, followed by a Schmitt trigger/contact plate with an isolation capacitor of 470 pF; - an RC network that converts the change in pulsewidth into a voltage. This voltage is about 2. 9-3. 2 V when the plate is touched (and 2. 6 V when it isn`t touched); - an LM339 comparator is used to compare the voltage at point C with a reference voltage (D). The latter is set to about 2. 8 V using a potential divider. As long as the contact plate is touched the output of the circuit will be active. To make the operation of the circuit clearer we have shown the signals at various points in Figure 2. The dotted line represents the signal when the plate is touched, the solid line when it isn`t touched. The reference voltage at D has to be set up once via potential divider R4/R5 (change the value of R4)....
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: