Touch Switch Using Transistor

About: I just love to do electronics and robotics...

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to actually construct a working device at that time. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley. The transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.

Most transistors are made from very pure silicon or germanium, but certain other semiconductor materials can also be used. A transistor may have only one kind of charge carrier, in a field effect transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Compared with the vacuum tube, transistors are generally smaller, and require less power to operate. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages. Many types of transistors are made to standardized specifications by multiple manufacturers.

Step 1: The Components

The components can be bought from Banggood. They are listed below with links of Banggood:


1. 2N2222A NPN Transistor (1pc) - https://m.banggood.com/50Pcs-TO-92-30V-0_6A-2N2222A-Triode-Transistor-NPN-2N2222-Switch-Transistors-p-1069780.html?rmmds=search

2. LED (1pc) - https://m.banggood.com/375pcs-3MM-5MM-LED-Light-emitting-Diode-Beads-Resistance-Lights-Kits-Bulb-Lamp-p-1027601.html?rmmds=search

3. 1K OHM/1000 OHM Resistor (1pc) - https://m.banggood.com/Wholesale-400pcs-Metal-Film-Resistor-Assortment-Kit-Set-20-Kinds-Value-Total-p-53233.html?rmmds=search (Banggood doesn't sell 1K OHM Resistors only, there are 20 kinds of them in this pack. But you are gonna use only 1000 OHM ones, with colour codes of Brown, Black, Red, Gold for each 1K OHM ones)

4. Breadboard (1pc) - https://m.banggood.com/Mini-Solderless-Prototype-Breadboard-170-Points-For-Arduino-Shield-p-74814.html?rmmds=search
You can also use this kit (I suggest this one) - https://m.banggood.com/MB-102-MB102-Solderless-Breadboard-Power-Supply-Jumper-Cable-Kits-Dupont-Wire-For-Arduino-p-933600.html?rmmds=search

5. 9V Battery (1pc) - Non-rechargeable - https://m.banggood.com/9v-Universal-Eastpower-Battery-for-Multimeter-Thermometer,etc-p-78472.html?rmmds=search
Rechargeable (directly rechargeable with phone charger) - https://m.banggood.com/ZNTER-S19-9V-400mAh-USB-Rechargeable-9V-Lipo-Battery-p-1070703.html?rmmds=search

6. 9V Battery Clip/Connector (1pc) - https://m.banggood.com/5pcs-Hard-Plastic-9V-Battery-T-type-Snap-On-Connector-150mm-Wire-Cable-Lead-p-945189.html?rmmds=search

7. 5V Buzzer (If you want to connect it to the circuit) (1pc) - https://m.banggood.com/5-PCS-Super-Loud-5V-Active-Alarm-Buzzer-Beeper-Tracker-95_5mm-for-Racing-Drone-p-1117207.html?rmmds=search


You may need 1pc of each item only, but you should buy multiple, so that you don't have to buy them again in the future. The number of components written in brackets says 1 for all of them, which means you need 1 in the circuit. It is not that you will find 1pc in Banggood.

Step 2: The Connections

The first thing you should do is learn how to use a breadboard properly. You will find it on YouTube.At first, insert the transistor to the breadboard. It has 3-pins, Emitter, Base, and Collector. When the flat side of the 2N2222A NPN Transistor is facing you, the leftmost pin will be Emitter, middle one the Base, and the rightmost will be the Collector. Remember it. Then connect the LED Cathode (the short legged pin; negative pin) to the Collector of the Transistor and put it's Anode (longer pin; positive pin) to a disconnected space of the breadboard. Then connect one end of the resistor to the LED Anode and the other end to a disconnected space of the breadboard. Then take a touch wire and join it to the Collector and to a disconnected space of the breadboard. Then take another touch wire and connect it to the Base and to a disconnected space of the breadboard. Now join the battery clip/connector to the 9V battery. Connect it's VCC (positive wire; probably the Red one) to the Resistor's disconnected side and connect Ground (negative wire; probably the Black one) to the Emitter of the Transistor. You're done.

Remember, the resistor colour codes for 1K OHM / 1000 OHM are Brown, Black, Red, Gold. Use 220 or 330 OHM resistors when connecting Buzzers. See resistor colour code diagram/table for more information. And do remember, colour codes for 1K, 220, and 330 Ohm resistors are different. Check them in the resistor colour code image.

Step 3: Finished - Let's Test It

Touch the two touch wires together, and you'll see the LED will stay on when touched, and off as you release your finger. Bring your friends or any family member. Touch one wire and tell your candidate to touch the other wire and them touch the candidate, and you'll see the magic.

This circuit is completed with an LED, but you can use a buzzer if you want, or you can connect both of them together. Good luck for your experiment.

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