Touch operated switches are an attractive project for DIY electronics but they are not so common in commercial products. The reason for this is that, although there are many different ways of implementing a touch switch (leakage, hum pickup, capacitance, albedo) all of them rely on body parameters which vary a lot with the person's body, age and environment so that a circuit which gives reliable operation with one development engineer may cause problems in use with, for instance, old folks living in arid areas. Nevertheless touch switches can give excellent results.
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This one is the equivalent to those banks of push buttons where you push any switch and it releases one already pushed in. I've only shown two stages but you can have 5 - or ten if you wish. Consider the state with the first stage on. Current flows from the 0v line through the 1K resistor, the LED and the bottom two transistors. The centre line will then be at about -10v.
Now touch input 2. The top transistor will pass current into the bottom transistor: the two bottom transistors will turn each other hard and suddenly on. But the 100n capacitor has no voltage across it so it takes a pulse of current as it charges up. Instantaneously he centre line drops to -12v and the LED which was on extinguishes. Since the current that was flowing through this LED also flowed through the first pair, these turn off. The first 'button' has been released. Quite a nice, simple circuit for a multi button touch switch. This is a timer or power switch. Touch the contacts and the switch turns on. After a preset delay it turns off again. Its output is from a pass transistor so you can use it to operate another circuit during its timeout period. Touching the contacts causes a current to flow through the 4M7 into Tr3's base turning it on. Its collector current turns on Tr2. The 10µ capacitor is not charged, so it charges up, holding Tr3 on. Meanwhile Tr2's emitter current turns on Tr1, applying power to the load.
While the 10µ is charging...
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....
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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....
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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.....
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