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ManualsBrandsCONRAD COMPONENTS ManualsToysDer Conrad-Adventskalender 2017

Foreword

Many are already anxiously awaiting the Advent season, since the electronics calendar starts with 24 experiments again. This year, the topic is "Operational

amplifier (op-amp) and sound converter." The focus lies on the four-fold op-amp LM324, which enables many interesting experiments, in particular, with the piezo

sound converter. Different noises can be produced and, with certain skill, even a simple musical instrument designed. The piezo converter can be used as either

microphone or vibration sensor, if weak signals are amplified by the op-amp.

All experiments can be successfully performed and tested without any prior knowledge. The assembly drawings will facilitate your task. However, someone who

takes a closer look at the circuits will be able to find other variants and possibly even use fewer wires than initially planned. As always, merely the structure and

expected function are presented in the description first. In addition, in most cases, there is a short explanation. Surely, all the basics of the electronics cannot be

given here, but if someone is curious they can make further own research.

Points are awarded for solving some additional tasks included in some experiments. You can decide for yourself whether a task is fully solved, otherwise you can

look for an arbitrator, maybe a family member or a friend. All the points are summed up in the end, and you will find out, whether you are an adept in electronics.

We wish you a lot of fun and a great Christmas time!

1 Electric noise

Behind the first door, you will find a central component of this electronics calendar: a piezo sound converter with connecting wires. The first box also contains

some wires. In addition, a 9V battery must be available. If no battery is available, for the first experiment, even a heavily used battery will suffice, which has

already become too weak for other devices. Hold both cables of the piezo sound converter connected to the battery. You will hear a crackle on the first touch. On

the second contact it remains quiet, because the sound converter is already charged. To discharge it, you can connect the two wires of the piezo panel directly or

with a piece of wire. You will hear a crackle again, and a repeated crackle when recharging. One precondition is, however, to avoid touching the bare ends of the

cables directly, because discharge is possible even in spite of the skin resistance.

Info: The ceramic piezo panel is at the same time a small capacitor with two metal plates and an insulator

between them. Electrical forces between the charges cause deformation of the insulator and thus the sound is

created. After the capacitor is already charged to 9V (Volt), the repeated connection to the battery does not matter

anymore and no sound is heard.

Mission: Crackling noises at even a higher volume can be produced by repeated reversing of the battery's polarity.

If you can demonstrate that, you get: 2 points.

2 Finding contact

Behind the second door, you will find a plug-in board and a battery clip for the 9V battery. The flexible wires of the battery clip are insulated and tin-plated at the

ends so that you can plug them into the contact holes of the plug-in board. However, they must be plugged in only once and then remain in the same position. If

you want to de-energize the circuit, just remove the battery from the clip, but leave the connecting wires connected. The board has a small wire built-in as a strain

relief cleat to restrict movement of the battery cable.

The connecting cable of the piezo sound converter must also, if possible, be plugged in only once and remain in the same position. An approach without any holes

thrust through the foil of the reverse side to introduce the cable proved its worth. Thus, the connectors of the piezo panel can stay in the same positions, even if this

component is not used in some experiments. It does not matter, by the way, which wire of the sound converter is used as the upper or lower contact, while it is

decisive for the battery that the positive (red) pole is always connected on the top.

Build a model using the blank wire as a switch. The upper connector of the sound converter must be alternately connected with the positive and negative pole of

the battery. Pull off the insulation of the wire and, using a wire cutter, cut to size the remaining wire, from which the switch contacts will be made. All other

connecting wires and the wire piece intended for strain relief of the battery cable must retain their insulation in the central part and be only stripped at the ends

over a length of about 5 mm. The plastic insulation is sufficiently soft to be stripped by fingernails. Alternatively, you can cut it round with a sharp knife without

scratching the wire, which otherwise would be easily breakable. Once everything is properly connected, the experiment can start. Using the self-made switch, you

can charge and discharge the piezo sound converter as often as you like thus generating noise each time.

But it can be done without a battery! Short-circuit the sound converter with the switch and press delicately the membrane with a pointed object. Open the contact

and only then remove the mechanical pressure from the panel, which is electrically charged thereby. When the contact is closed again, a clear crackle is heard. But

Summary of content (12 pages)

PAGE 1
Foreword Many are already anxiously awaiting the Advent season, since the electronics calendar starts with 24 experiments again. This year, the topic is "Operational amplifier (op-amp) and sound converter." The focus lies on the four-fold op-amp LM324, which enables many interesting experiments, in particular, with the piezo sound converter. Different noises can be produced and, with certain skill, even a simple musical instrument designed.
PAGE 2
not only mechanical pressure can charge the piezo panel, but a temperature change as well. Warm up the panel by touch with open contact. As a result, it will charge and generate noise when discharging. After a while, cooling can produce a crackle again. Mission: Put the entire model for some time into the cold outdoors. Take it back into the warm indoors and obtain at least five clearly audible crackles in a row: 3 points. 3 Charging and discharging Behind the third door, there is a 2.2 kΩ (2.
PAGE 3
Mission: Press the switching contact so that both wires are only lightly touching or stroking each other. This generates a scratchy sound in the loudspeaker of the kind often heard in the old telephones. The contact is neither reliably closed, nor fully opened. The LED is flickering. However, much skill is required to achieve this effect: 4 points. 5 Has the integrated circuit landed well? Open the fifth door.
PAGE 4
Mission: Touch only lightly the LED anode and the input. It will weaken the LED's light, but it won't fully go off: 4 points. 7 Afterglow after a touch Behind the seventh door, you will find a brand new component, namely a 100 nF (nanofarad) capacitor. It is a ceramic disk capacitor with the 104 (100,000 pF, picofarad) label. Integrate it into your circuit. The LED this time is connected to plus and thus the idle mode is reversed. In normal state, the LED is off.
PAGE 5
9 From red to green Behind the door number 9, there is a 4.7 kΩ resistor (yellow, violet, red). It is intended as a series resistor for the green LED. As both LEDs are now at the input, the output voltage defines the brightness ratio between the two colours. If the wire switch is closed, the red LED is on. Once the switch is opened, the red LED slowly gets weaker and the green - brighter, until, finally, only the green LED is on.
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any desired colour mix can be set. Info: the basic circuit is an integrator again so this time the input current depending on the switch setting can be positive, zero or negative. In the neutral middle position of the switch, the output voltage should not change. As a matter of fact, the unavoidable insulation error of the electrolytic capacitor and the output current of the op-amp leads to slow change. Mission: modify the switch into a double motion detector using four bare wires.
PAGE 7
Info: the functionality of this circuit cannot be easily understood. Behaviour of an ideal operational amplifier would be quite different. However, specific features of the bipolar op-amp with PNP input stages are used in this case. The input current is about 30 nA, so there is a voltage drop of 10 mV at the inverting input and only 3 mV at the non-inverting input. The difference is sufficient to achieve a steady idle state. The sensor must add at least 7 mV to change the state.
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Mission: Put the circuit for several minutes in the cold outdoors and examine the influence of lower temperatures. Put the circuit directly onto the heater and look for the warmest place in the room: 4 points. 16 As a Geiger counter… Behind the 16th door, you will find a next disk capacitor of only 10 nF (label 103) this time. Integrate it into the tone generator. Modified resistors are also used to adjust the tone.
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18 Light organ Open the door number 18, and take out a 330 kΩ resistor (orange, orange, yellow). Besides, integrate the LED as a light sensor again. Now you can change the tone by a torch or any other light source. The closer the lamp the higher the frequency. The expression "light organ" mostly stands for a device, where the sound is controlled by the light. Here, it is vice versa: Light defines the tone pitch. Info: The circuit uses again a buffer amplifier for an uninterrupted tone generation.
PAGE 10
output frequency drops both at higher and at a lower input voltage. Since the bi-polar op-amp does not operate across the entire voltage range, deep and less deep phases can be found. Mission: in addition, integrate an LED with a suitable series resistor so that the signal sequence of the slower oscillator can be seen: 3 points. 21 Light alarm You will find a 3.3 MΩ resistor (orange, orange, green) behind the door number 21. It will be used in a slow oscillator.
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purpose there are two buffer amplifiers and the electrolytic capacitor energised by operating voltage. Mission: Warm up two capacitors simultaneously, so that the oscillators always have the same rising frequency. This requires a little practice and much skill, as you must detect by sound, when one of the oscillators tends to escape the coupling: 3 points. 23 Organ for two hands The second 10 nF (103) capacitor is behind the door number 23. It is meant to be used to make a two-tune organ.
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transitions. Mission: 24 experiments have been successfully completed, but we are still far from exhausting all possibilities. A vast variety of circuits can be built using available components. Invent a circuit of your own, which differs from all presented models as far as possible, and get: 10 points.