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ManualsBrandsCONRAD COMPONENTS ManualsScience KitsCourse material Basic Elektronik 14 years and over

Understanding and using electronics

Burkhard Kainka

1. Step: Introduction.......................................................................................................................................1

Patch panel.....................................................................................................................................................1

Battery............................................................................................................................................................2

Light-emitting diodes.....................................................................................................................................3

Resistors.........................................................................................................................................................3

NPN transistors..............................................................................................................................................4

PNP transistors...............................................................................................................................................4

MOSFET........................................................................................................................................................4

Capacitors ......................................................................................................................................................4

Electrolytic capacitors....................................................................................................................................5

2. Step: Current gain ......................................................................................................................................5

3. Step: Positive and negative reversed..........................................................................................................6

4. Step: Follow-up control .............................................................................................................................6

5. Step: Contact sensor...................................................................................................................................7

6. Step: Motion detector.................................................................................................................................8

7. Step: LED as light sensor...........................................................................................................................9

8. Step: Constant brightness...........................................................................................................................9

9. Step: Temperature sensor.........................................................................................................................10

10. Step: On and off...................................................................................................................................11

11. Step: Firing and erasing .......................................................................................................................11

12. Step: Push-pull flasher.........................................................................................................................12

13. Step: Simple LED flasher ....................................................................................................................13

14. Step: LED flashing light ......................................................................................................................13

15. Step: MOSFET touch sensor ...............................................................................................................14

16. Step: Sensor-dimmer............................................................................................................................15

17. Step: Electrometer................................................................................................................................15

18. Step: LEDs as photovoltaic cells .........................................................................................................16

19. Step: Capacitor temperature sensor .....................................................................................................17

20. Step: Minute light ................................................................................................................................17

21. Step: Smooth flasher............................................................................................................................18

1. Step: Introduction

Since the transistor was invented, things have only gotten better with electronics. Today we are surrounded by

devices whose integrated circuits contain many millions of transistors. But at the same time fewer and fewer know

exactly how a (single!) transistor actually works. The gap between using and understanding electronics is constantly

increasing. It is very simple: take a few transistors and do a few simple experiments – and an infinite number of

possibilities open up. Many problems can be solved with simple transistor circuits. So get creative!

A transistor is a component with three connections and is for controlling the electric current. The amount of current

that flows is influenced via a control connection (gate). There are essentially only two types of transistor. The bipolar

transistors are made of layers with N and P semiconductor material. Depending on the sequence of layers, there are

NPN transistors (e.g., BC547) and PNP transistors (e.g., BC557). By contrast, unipolar transistors consist of only one

semiconductor channel whose conductivity is changed by an electric field. For this reason they are called field effect

transistors (FET). A typical representative is N-channel MOSFET BS170.

This educational kit will make your start into electronics easier. First of all, the components are presented. The

individual experiments are done on a breadboard. For each experiment there is a circuit diagram and a set-up photo.

The photo is only meant as a suggestion. You can also arrange the components differently. The connection wires of

the individual components were in some cases shortened for the photos to give a clearer view. But you should use the

connection wires unshortened so that they can also be used for other experiments.

Patch panel

All experiments are set up on a laboratory experimental board. The patch panel with altogether 270 contacts in a

2.54 mm grid provides for secure connections of the components.

Summary of content (19 pages)

PAGE 1
Understanding and using electronics Burkhard Kainka 1. Step: Introduction.......................................................................................................................................1 Patch panel .....................................................................................................................................................1 Battery..................................................................................................................................
PAGE 2
Fig. 1: The experimental board (B_Steckbrett.jpg) The patch panel has 230 contacts in the middle area which are each electrically connected by vertical strips with five contacts. In addition, there are 40 contacts at the edge for the power supply, consisting of two horizontal contact spring strips with 20 contacts. The patch panel thus has two independent supply bars. Fig. 2 shows all internal connections. You can see the short contact rows in the middle area and the long supply bars at the edge. Fig.
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1.5 V 4.5 V 6V 9... 12 V Fig. 4: Schematic symbols for various batteries (Bat.gif) Light-emitting diodes The educational kit contains two red LEDs and a green and a yellow LED. With all LEDs, the polarity must always be attended to. The negative terminal is called the cathode and is on the shorter connection wire. The positive terminal is the anode. Inside the LED, you can see a cup-like holder for the LED crystal which is at the cathode.
PAGE 4
A resistor with the yellow, violet, brown and gold coloured rings has the value 470 Ω with a tolerance of 5%. In the educational kit there are two resistors with the following values: 470 Ω 1 kΩ 22 kΩ 470 kΩ yellow, violet, brown brown, black, red red, red, orange yellow, violet, yellow NPN transistors Transistors are components for amplifying small currents. The educational kit contains two silicon NPN transistors BC547B. The terminals of the transistor are called emitter (E), base (B) and collector (C).
PAGE 5
Fig. 10: A ceramic capacitor (B_Kondensator.gif) Electrolytic capacitors You get large capacitances with electrolytic capacitors. The insulation consists of a very thin layer of aluminium oxide. The electrolytic capacitor contains a liquid electrolyte and wrapped aluminium foil with a large surface. The voltage may only be applied in one direction. A leakage current flows in the wrong direction and gradually degrades the insulation layer, which leads to destruction of the component.
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Fig. 13: Current gain (F_NPN1.jpg) The LEDs are for indicating the currents. The red LED shines brightly, the green one barely. Only in a completely darkened room can the base current be seen as the weak shining of the green LED. The difference is an indication of the large current gain. 3. Step: Positive and negative reversed A PNP transistor has exactly the same function as an NPN transistor, but with reversed polarity. The emitter is thus now at the positive pole of the battery. green red Fig.
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green red Fig. 16: Delayed switching-off (Schaltung3.jpg) The discharging time is considerably extended by the large base resistor. After about two seconds the electrolytic capacitor is already mostly discharged. But after this time, the base current still suffices for a slight modulation of the transistor. The collector current decreases only gradually. Fig. 17: The afterglow electric torch (F_NPN3.jpg) The LED shines with full brightness as long as you keep the key switch pressed.
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Fig. 19: The contact sensor (F_ Darlington1.jpg) 6. Step: Motion detector This circuit has a sensor wire at the input of the first transistor. If someone moves in the vicinity of the wire, the LED lights up. Through motion on an insulating background, every person charges him-/herself electrically without noticing it. If you then move in the vicinity of conductive objects, the electrostatic forces lead to a shifting of electric charges, i.e., to a small current, which is highly amplified here.
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7. Step: LED as light sensor This light sensor controls the brightness of an LED. When light strikes the sensor, the LED goes on; in darkness it stays off. Actually, practically no current flows through a diode if it is put to a voltage in reverse direction. However, there is actually a very small reverse current, e.g., in the range of a few nanoamperes which normally can be disregarded. The high gain of the Darlington circuit, however, allows experiments with extremely small currents. Thus, e.g.
PAGE 10
Fig. 25: Stabilisation of LED brightness (Aufbau7.jpg) Check the results with a new battery and a heavily used one. As long as a certain residual voltage is present, the LED stays almost as bright. With only one LED, the battery voltage may be lower than with two LEDs, in which latter case at least about 6 V still have to be present. 9. Step: Temperature sensor This circuit shows temperature differences via the LED brightness. It is enough to touch the temperature sensor with your finger.
PAGE 11
10. Step: On and off Now it goes digital: while more or less current flows in an analogue circuit, a digital circuit is either completely on or completely off. The states On and Off are also designated as One and Zero. The circuit depicted here can be seen as a basic module of computer technology. A circuit with two stable states is called a trigger circuit or also a flip-flop circuit. An LED is either on or off, but never “half-on.” Fig. 28 shows the typical circuit of a simple flip-flop.
PAGE 12
green Fig. 30: Conducting and blocking (Schaltung10.jpg) With a short connection S1, you fire the circuit so that the LED shines. With S2, by contrast, the conductive state can be erased. S3 switches the LED on, but at the same time erases the conductive state of the transistors. After opening S3 the LED is thus off. Fig. 31: On or off (Aufbau10.jpg) 12.
PAGE 13
Fig. 33: A slow alternating flasher (F_Blinker1.jpg) 13. Step: Simple LED flasher A flasher unit in a motor vehicle usually activates only one lamp. Another flip-flop is set up here that automatically switches back and forth. The circuit requires only one capacitor. Two transistors in an emitter circuit form an amplifier. The feedback from the output to the input passes via a capacitor that repeatedly charges and discharges itself. green Fig. 34: The multivibrator (Schaltung12.jpg) Fig.
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green Fig. 36: The flashing light circuit (Schaltung13.jpg) Remove from the circuit the 1 kΩ resistor that is parallel to the LED: the pause between flashes of light is considerably prolonged. The left transistor blocks only when the electrolytic capacitor is completely discharged. Only then does its collector voltage slowly increase so as to enable a new pulse. Fig. 37: LED flashing light (Aufbau13.jpg) 15.
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divert any charges. There is particular danger for the transistor if two persons touch the same circuit. Since the two can be differently charged, a discharge via the transistor can result which destroys it. Fig. 39: Charging and discharging the gate (Aufbau14.jpg) 16. Step: Sensor-dimmer With an additional capacitor between gate and drain, intermediate states between “completely on” and “completely off” are also preserved.
PAGE 16
The initial state after switching on is indeterminate; the transistor could thus be completely blocked or completely conductive. In both cases, small differences in the gate voltage have no effect. There is thus a start switch with which you briefly connect gate and drain. The gate voltage adapts to the middle range at around ca. 2 V. Fig. 42: The electrometer (Schaltung16.jpg) Fig. 43: Detection of electric charges (Aufbau16.jpg) 18.
PAGE 17
Fig. 45: The light sensor (Aufbau17.jpg) 19. Step: Capacitor temperature sensor A ceramic capacitor with 100 nF can be used as a temperature sensor. Such a capacitor has a large temperature coefficient. The capacity is diminished with heating. In this experiment, the switch must initially be closed and then opened again. The gate voltage automatically adapts to the threshold voltage of approximately 2 V; the LED shines. There is a voltage of about 7 V at the 100 nF capacitor.
PAGE 18
green Fig. 48: Slow capacitor discharge (Schaltung19.jpg) Fig. 49: The minute light (Aufbau19.jpg) 21. Step: Smooth flasher An LED flasher with smoothly swelling and ebbing brightness can, with a suitable frequency, help the viewer relax. The brightness follows a sinus wave. This circuit activates two LEDs precisely in phase opposition. The light thus continuously changes with smooth transitions between red and green. green red Fig. 50: A phase shifter oscillator (Schaltung20.
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Fig. 51: The soft flasher (Aufbau20.