Conrad 4019631150066 Operation Manual
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
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 k (2.2 kohms) resistor. It is labelled by three colour rings (red, red, red). The fourth, golden ring indicates the 5% accuracy
class. Connect this resistor in parallel to the sound converter. It will ensure quick discharge. Therefore, a simple contact is enough this time. The noise is generated
each time when the contact is closed or opened. The resistor consumes energy so do not leave the switch closed for a long time. However, if possible, the battery
should last until the end of the experiment.
Info: You can easily estimate the moment of the battery discharge. The amperage is 9V divided by 2.2 k i.e.
around 4 mA. For the alkaline battery with the capacity of 500 mAh it makes 125 hours or about five days until the
battery goes flat.
Mission: Make two touch-contacts and connect your skin resistance in a row to the available 2.2 k resistor. The
skin resistance is some 100 k, so that with small current the discharge is much slower and quieter. The resistor
only plays a protective role and restricts the current in case of an inadvertent direct contact of the sensor contacts.
Resistance can be changed by touch of different strength. The purpose is that the crackle is only generated with
every closing, but not opening the switch: 4 points.
4 Light and sound
Behind the door number 4 you will find a red light diode (LED). Integrate the LED into the positive lead of your model so that you know, when the switch is closed
and the current flows. When installing an LED, you need to observe correct polarity.
The LED has two different connectors. The short wire is the negative (cathode), and the long wire is the positive (anode) pole. Once the LED is integrated, it is
difficult to see which wire is the short one. There is, however, an additional marking. The broader lower edge is flattened on the cathode side. Besides, the bigger
bracket in all LED across this calendar is connected with the cathode inside the LED.
Info: In a series connection, the battery voltage of 9V is divided to a single load. Now, a voltage of about 2V is
applied to the LED, and 7V to the resistor. Since the voltage at the piezo sound converter is only at 7V, the crackles
caused by switch touching are now a bit quieter. Since our ears are accustomed to a much broader range of sound
levels, the difference is practicable unnoticeable.
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. Behind it, you will find the most important component of this calendar, the fourfold op-amp LM324. This IC (integrated circuit) with 14
connecting pins contains four separate amplifier units each with two inputs and one output. The amplifiers themselves are interchangeable, but both operating
voltage connectors may never be confused, otherwise the IC can be damaged. The plus connector is on pin 4, while the minus connector is on pin 11. However,
normally, the plus pole is on the top, and the minus pole - on the bottom of the experimental board. Therefore, the IC must be used in such a way that the label is
upside down.
Imagine that the fourfold op-amp is a spacecraft, which is going to land on Mars. Everyone is anxiously awaiting the first signs of activities proving that the
spacecraft has landed properly. In this case, light of the red LED shows that everything has worked out well. And the resistor prevents damage if an error occurs.
Unlike on Mars, anything can now be easily rectified and the entire circuit retested.
Info: An op-amp amplifies the voltage difference between its two inputs. If the difference is
significant, the output is either fully on or fully off. In this case, the voltage at the (+) input is
higher than it is at the (–) input, therefore the LED is on. Normally the IC is powered by the
full operating voltage, but this time there is also a protective resistor connected to the plus
lead.
Mission: Modify the circuit so that another of the four potentially used amplifiers will be used
(1 point). Or test the same with each of the other three amplifiers (3 points).
6 Contact sensor
Behind the door number 6, there is a 330 k resistor (orange, orange, yellow). Make a circuit with an open op-amp input. Two wires with bare ends lead outward.
In normal state, the LED is on. It goes off if the two input wires are connected. It is enough to touch both wires by the finger, as the conductivity of the skin is
sufficient to change the state. If only one wire is touched at the (+) input, the LED can be on or off and sometimes it may flicker. If electric cables are in close
proximity, humming or buzzing may come out of the loudspeaker.
Info: The voltage between the two inputs is amplified about 100,000-fold. However,
in this case the inverting input (–) is directly connected with the output. The negative
feedback thus created reduces the voltage amplification to one (1). At the output is
thus almost always exactly the same voltage as at the non-inverting input (+).
Although the voltage amplification is only 1-fold, the op-amp provides very strong
current amplification. Therefore, the amplifier is sensitive to weak interference
signals.
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. However, if
the wires are short-circuited or touched by the finger, the LED switches on. It glows for a long time after that and only slowly goes off. Thus, a nightlight can be
made, which is switched on by simple touch and goes off again by itself.
Info: This circuit does not function with just any op-amp, but is dependent on a
specific feature of this op-amp type. The LM324 contains a bipolar operational
amplifier with PNP input stages with operational voltages down to negative ones
and even lower. The basic current of the input transistors is about 30 nA, i.e. 0.03
A. Current this weak only slowly charges the capacitor at the input. The input
µ
voltage increase rate is about 0.3 V/s. Therefore, it takes a bit longer than 20 s until
the voltage exceeds 7V and the LED goes off.
Mission: touch the inputs so delicately that the LED does not go off yet, but gleams
evenly weakly. You must find yourself how you create the proper resistance by
your fingers and get: 3 points.
8 Light control
Behind the eighth door, there is another LED. It is green and should be placed at the output of the op-amp instead of the red LED, while the red LED receives a new
task: it will be a photodiode and thus an effective light sensor. Please note the installation direction with the cathode at the input of the op-imp. If you expose the
red LED to a bright light of a torch, the green LED lights up.
Info: A photodiode has the same structure as any other diode or light diode. An
insulating barrier layer is formed in the locking direction, which prevents current
flow. However, if light penetrates the barrier layer, some single electrons are
released from their ties and can move freely. The current flows. Since an LED
crystal only has small surface, only little light gets into creating weak photocurrent. In this case, only 30 nA of it suffices to switch on the LED.
Mission: Integrate an additional capacitor as on day 7. Thereby, switching on is
decelerated, and afterglow of the green LED can be observed: 2 points.
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