Content 1 Preparations ................................................................................. 3 2 Simple LED lamp .........................................................................4 3 More colors: red and green ......................................................... 7 4 Standby light for the night............................................................8 5 Adjustable brightness ................................................................ 10 6 Amplify current.......................
23 Intermittent flasher ..................................................................44 24 Flickering fire............................................................................45 25 The special LED light................................................................
1 Preparations At the heart of this study package are light-emitting diodes and transistors, which make even complex applications possible. We have also included the necessary information on how all of this works, for the curious among you. The study package contains the following components for assembling and connecting the components: a breadboard to set up all the experiments; a 9V battery clip to connect the battery; a dual four-port switch; a two-wire fuse; and five cables for the breadboard.
the breadboard. Use a needle to first pierce small holes into the protective film on the back of the board and then insert the wires from below. That way they are adequate secured. Switch and fuse should be positioned exactly as shown. We will use this set up in all of the coming experiments. We also have six light emitting diodes (LEDs). Five LEDs come in the colors red, yellow, green, blue and pink, and there is a red flashing LED with a more transparent housing and inside you can see a tiny chip.
The direction the LED is installed is very important. An LED has a shorter leg (cathode = negative pole) and a longer leg (anode = positive pole). Inside the LED you can make out a slightly larger holder at the minus side, which carries the actual LED crystal. After everything is set up and double-checked, we need to connect the battery - and now you have got a red LED light with a switch. If you push the left switch to ON, the red LED goes on. If this doesn’t work, check the setup again.
Circuit diagrams You don’t necessarily need the diagrams in this manual in order to successfully set up the experiments. But they help you to better understand everything. A circuit diagram shows the wiring of components in a simplified way using switching icons for each component. Once you get familiar with the diagram, you will easily understand how everything works together. The battery has six 1.5V battery cells. The longer dash indicates the positive pole. The fuse is drawn as a box with a wire.
3 More colors: red and green Here we are going to install a green LED in series with the red LED. Both LEDs will turn on together. You can turn both on and off together using the switch. Series circuit Two or more components connected in series carry the same current. This is a “branchless circuit” because the components are connected along one path. This means that the current is the same anywhere. You can easily test this by swapping both LEDs. The brightness remains exactly the same.
Simplified circuit diagram of a series connection 4 Standby light for the night Here we will install another resistor with 330 kΩ (330 kilo ohms). The resistor has the color rings orange, orange, yellow and an extra golden ring. The greater the resistance the less current flows. Our first resistor had only 4.7 kΩ (yellow, purple, red) and the light was relatively bright. By using the larger resistor, the LEDs will only glow dimly.
Resistors and their color rings The color rings on the resistors stand for numbers. They are read by starting with the ring that sits closer to the resistor edge. The first two rings stand for two numbers, the third for zeros. Together they represent the resistance in ohms. A fourth ring indicates the accuracy. All resistors have a golden ring.
This means that the value indicated by the color rings could be 5% greater or smaller. Your first resistor is read as follows: yellow = 4, purple = 7, red = 00, together 4.700 ohms, or 4.7 kΩ. The resistor color code Color Black Brown Red Orange Yellow Green Blue Purple Grey White Ring 1 Ring 2 1st number 2nd number 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 Gold Silver Ring 3 Multiplicator 1 10 100 1000 10000 100000 1000000 10000000 0.1 0.01 Ring 4 Tolerance 1% 2% 0.
resistors when both switches are on. But the difference to the third level is so small you wouldn’t even notice.
Voltage, resistance and current We already know that electrical voltage is measured in volts (V). The battery has 9 V. Resistance is measured in ohms (Ω) or kilo ohms (1 kΩ = 1,000 Ω). But there is another very important measurement: electrical current is measured in amperes (A) or in milliamps (1 mA = 1/1000 A) in the case of low currents.
The larger 330 kΩ resistor delivers a current of approximately 0.015 mA and will thus run four years on just one battery. Saving power pays! 6 Amplify current The most important component of this study package is the transistor. You should not mix up the three terminals. They are called emitter (E), base (B) and collector (C). The emitter connects to the negative terminal of the battery. Therefore, the transistor’s flat side with the label should point to the left.
build machines, calculators or entire computers with such basic circuits. Transistors A transistor contains a silicon crystal. Silicon (Si) is found in normal quartz sand in large quantities (quartz = silicon oxide). It belongs to the group of semiconductors; these substances neither conduct electric current as well as metals nor do they have the properties of insulating materials such as glass or rubber.
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7 An alarm system For this little alarm system, we will need a second cable. This is used as the connection between the base, which shuts off the collector current, and the emitter of the transistor. If you pull out the cable, an alarm is triggered, and the red LED goes on. You could build an alarm system using a thin wire that breaks, if someone opens a window or door. If formed as an alarm loop, the wire could also secure several windows and doors.
Attention: fuse and switch are not shown in the circuit diagram, they are however always part of it.
8 Off at the push of a button We will use a push-button switch instead of the alarm loop of the last experiment. In the normal state, the switch is open. But when you press the button, the contact will close, and this will turn off the red LED. The NOT circuit Isn’t it strange, we are closing a contact and switch on current, but by that another current is switched off. Switching on causes switching off, that is the exact opposite.
9 Keep on the glow The capacitor in this study package acts as a small energy storage. It is an electrolytic capacitor (short, e-cap). The important thing about this e-cap, you need to pay attention to polarity, just like with an LED. The negative pole is indicated by a thick white line and connects to minus. Attention! Do not install an electrolytic capacitor the wrong way round. If an e-cap’s plus and minus are reversed, its insulation won’t work.
perfect night lamp, because you can gradually adjust to the dark. Capacitor A capacitor has two metal plates or metal films that are isolated from each other and do not come in contact with each other. If connected to a battery, they become electrically charged and will store electrical energy. The capacitance of a capacitor, that is the amount of electrical charge a capacitor can store at a given voltage, is measured in farad. The unit is named after the well-known researcher Michael Faraday.
10 Red and green in sync Besides the LED crystal, the red flashing LED has a circuit which switches the LED current on and off again and again.
If you install the LED as laid out in the set-up plan, the green LED will also turn on and off. The result is a red and green flashing light that starts when you push the button switch and which then gradually fades away. If the LEDs don’t flash, you have probably installed the normal red LED, which you can recognize by its somewhat matt colored housing. The flashing LED The flashing LED has an electronic switch that consists of a transistor. Nevertheless, other transistors and components are still needed.
11 Three LEDs with turn-off delay Now we are going to install a third LED together with another 4.7 kΩ resistor (yellow, purple, red).
not flash because it is not in series with the flashing LED. It will slowly die away like the other LEDs. At the very end of the cycle, only the red LED continues to glow. The green LED and the flashing LED go fully dark, because together they have a greater voltage demand.
12 Flashlight trio in sync We will arrange the circuit now in a way that all three LEDs will go fully dark in between the flashing cycles. We are going to use a 1 kΩ resistance (brown, black, red). The red flashing LED utilizes the transistor to turn the red and green LEDs on and off. As a result, all three LEDs are flashing. Remove the 1 kΩ resistor out of the circuit and you will see that only the flashing LED will flash, the other two LEDs are steady lit.
13 Touch switch We add another transistor to the first to increase amplification even more. Both collector terminals are interconnected; the emitter of the first transistor goes to the base of the second. This circuit is called Darlington circuit. We will use this to build a touch switch.
The Darlington circuit Connecting two transistors the way we see in the diagram is called Darlington circuit. The amplification of two transistors is greater than using just one. This holds especially true for this circuit, where the already amplified current is amplified even more by a second transistor. The inventor Sidney Darlington, who came up with this idea in 1952 gave the circuit its name. Both collectors are interconnected, and the emitter of the first transistor flows to the base of the second.
14 LED light sensor In this experiment, we are going to use a yellow LED as a light sensor. It is installed the other way round unlike we usual do and in consequence, it actually does not conduct electricity. But a small current flows as soon as light falls on the LED, very similar to a photodiode. This is then amplified by the two transistors and will cause the other two LEDs to light up. Try this with a flashlight. The more you illuminate the yellow LED, the brighter the two other LEDs will glow.
Besides light-emitting diodes, there are rectifier diodes and photodiodes made from silicon, the very same material that is used in the transistors. A photodiode has a particularly large surface to have as much light as possible enter into the boundary from the outside. There, the light ensures that the isolating effect of the boundary layer is lifted in part and current flows. An LED is similar in structure, but its surface is very small. Thus, the light-dependent current is also very small.
15 Extra switch for dark nights We expand the light sensor by an additional switch. The second switch makes it possible to turn on the LEDs at night. We will install it parallel to the light sensor, where it will be able to deliver enough base current to turn the LED on when it is dark. Instead of the switch, you could also install two contacts for a touch sensor or simply touch the wires of the LED sensor.
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The PTC fuse We are using fuses in all our experiments. Because if a short circuit happen, it could cause a wire to become burning hot. Or the battery could heat up and discharge quickly, or in the worst case, the battery could also explode. This is why we use a fuse to prevent such worst-case scenarios. Most fuses simply blow in response to a short circuit. But this here is a special self-resetting fuse also known as PTC fuse.
however, will be dimly lit due to the small base current still flowing though that other transistor. It is impossible to predict the LED that will turn on. You can however switch the state by bringing a wire in contact with one of the base terminals, which will generate a short electrical pulse due to charges present at random. More often than not, it doesn’t always work the first time. But you can do it safely by connecting the base to the emitter at the currently conducting transistor.
17 Reaction games You can use two buttons to bring some system into the last flipflop experiment and have it adopt the state you choose.
not disturb! And green means: Communication allowed. At the same time, this experiment is also an electronic game. Every switch can turn off the base current of its associated transistor, whereby also the connected LED goes off. Normally you would press only one button or one after the other. However, if you press both buttons at the same time, both LEDs will go dark. But when you release the buttons, only one LED will go on, and no one can foretell which is the one that turns on.
18 Four-color switch Today we are using the purple glowing LED for the first time. The housing is whitish, but in reality, the LED has a purple glow. We use the RS flip-flop of the last experiment and expand it by four LEDs. Just like before, each transistor has one LED in the collector line, but the other LED is installed into the emitter line. That way red and yellow will always glow in sync while at the other side we have purple and green.
Structure of the purple LED Actually, the LED crystal of the purple LED emits blue light. But the crystal is covered with a fluorescent material that captures part of the blue light and emits it as red light. So in reality the purple LED emits two colors: red and blue and thereby creates the composite color purple.
19 Simple RS flip-flop A very basic flip-flop can be built with just one LED and three resistors. The two buttons are used to switch the LED on and off. Such a circuit is also called RS flip-flop. The abbreviation stands for Reset (reset = switch off) and Set (set = switch on). The RS flip-flop is an important element in digital electronics and computer technology. The two-transistor circuit is again based on the fact that each transistor can turn off the base current to the other transistor.
LED on. You may also want to find out what happens when you install the flashing LED.
20 Temperature sensor We will modify our last circuit just a little bit, but it will behave totally different and will respond to different temperatures. The 1 kΩ resistor (brown, black, red) delivers base current to the left transistor. The LED is neither fully on nor fully off, but glows steadily and very dimly. Now, if you touch the right transistor with two fingers, it warms up a bit. The LED will glow a bit brighter.
21 Slow flasher Rather than using the red flashing LED with its built-in flasher we will build our own flasher. The circuit is a bit like the flipflops of our previous experiments. The main difference is that this time we are going to install a capacitor. The base current flows through the capacitor for as long as the capacitor is charged or discharged. After that, the flip-flop automatically changes state. Flashing speed and the time the LED is lit or dark depends on the dimensioning of the components.
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22 Transistor flasher in three colors We will install an additional 10 kΩ resistor (brown, black, orange) in series with the capacitor into the flashing circuit of our last experiment. This will make the on-off ratio more balanced. Another change involves the LEDs. The right transistor can control more than just one LED. Here we have three of them flashing in sync. The oscillator A circuit that automatically generates vibrations is called an oscillator.
23 Intermittent flasher The flasher gets a fourth LED. This time we are also using the flashing LED, which we install parallel to the green LED. Thus, the red flashing LED and the green LED are always flashing alternately. Flashing is now faster compared to our self-made flashing circuit. You can see a series of flashing pulses, where the flashing LED is flashing about six times together with the green LED and then stops. The flashing pulses of the other LEDs are slower.
24 Flickering fire In this experiment we intend to create a soft flickering that simulates a campfire. We will add a third brightness level between on and off to our circuit.
installed parallel to the flashing LED and will go on whenever the flashing LED is off. This creates a complex flashing pattern reminiscent of the flickering of a fire.
25 The special LED light One color was missing up to now. So here, we are now installing the blue LED. The intermittent red and blue alternating flasher is particularly beautiful and attracts everyone’s attention. And so many extensions with very different colors are possible.
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Impressum Dear Customer! This product has been manufactured in accordance with the applicable European directives and therefore bears the CE marking. The intended use is described in the instructions enclosed. You alone are responsible for compliance with applicable rules if you use the product for other purposes or in the case of modifications to the product. Please build the circuits exactly as described in the instructions. The product may only be passed on together with the instructions.
