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Foreword
As in recent years, Conrad Electronics again has a new calendar in 2016, also, with 24 experiments for
December 1 through 24. The topic is digital electronics. The experiments deal with digital counters with
the CMOS chip 4060. This IC contains 14 digital divider flip-flops as well as a clock oscillator with
multifaceted uses. It enables very different and very versatile applications that are not only educational
but also fun. At the end there is a circuit that can be hung on the Christmas tree to represent a wood
fire and falling stars.
There are various ways to use the electronics calendar. One person might simply wish to build
everything exactly according to plan and enjoy the success; another wants to understand it exactly. The
experiment descriptions should satisfy both. For this reason, the construction and the function are
always described only as briefly as necessary for the successful construction. Afterwards, the technical
background is explained in brief. Thus one finds the key ways with which one can also go on to look
for more information. In any case, the experiments provide the greatest pleasure when one works on
them with others. Parents and grandparents can perhaps pass on valuable experience and pique the
interest of children and youths.
Using the available parts, one can also build significantly more circuits than can be shown here.
Someone who works through the presented experiments with interest will quickly find further circuit
variants and similar applications. And completely new circuits can also be developed. No limits are
placed on your ingenuity!
We wish you great fun and a happy Christmastide!
1 The LED test
The first test in Advent should cause an LED to light up. An LED must never be connected directly to a
power source; one always needs a series resistor as well. Without this resistance, the LED would be
destroyed by too much current! The LED must be installed in the correct direction. It has two different
connections. The short wire is the negative terminal (cathode C); the longer wire is the positive terminal
(anode A). The wider lower edge is flattened on the cathode side. Also, on all LEDs in this calendar, the
larger bracket inside the LED is connected to the cathode.
Behind the first door, you will find a red LED and a resistor that matches it. You will also need a 9-V
block battery. The first test must be carried out especially carefully. Attention: avoid looking directly
into a lighted LED from short distances of less than one meter. Bright LEDs can cause retinal damage.
Avoid having both LED contacts ever touch the battery terminals at the same time! The resistor must
always be connected in series; otherwise, the LED burns through. Hold both components to the battery
as shown in the diagram. The LED lights up brightly.
One presents electronic circuits clearly in circuit diagrams. There is a symbol for each component. The
LED consists of a triangle for the anode and a straight line for the cathode. That signifies the current
direction. Two short arrows pointing outward stand for the light that is emitted. The resistor is shown
as a rectangular box. Every resistor has a specific resistance value. In this case, it is 10,000ohms = 10
kilo-ohms (10 kΩ, in the circuit diagram 10k for short). The actual component is marked with coloured
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bands (brown, black, orange for 10,000 and gold for potential deviations up to +/-5%).
The circuit diagram shows a series circuit. The current runs through the battery, resistor and LED. In this
case, the resistor has the task of limiting the amperage to a useful value. The higher the resistance, the
smaller the amperage. At 10 kΩ, the LED is in fact operated far below its maximum permitted current,
but it already lights up sufficiently brightly.
2 Battery connection
The second door hides a battery clip for the 9-V battery. Rebuild the test from the first day, but
somewhat differently. Use the battery clip and make sure that the black connection wire is the negative
terminal and the red the positive terminal. It is imperative that you avoid short-circuiting the battery,
that is, creating a direct connection between the two terminals. In the case of a short, the battery could
become very hot, and if the short lasts for a longer time, in extreme cases the battery could even
explode. Plus, short circuits reduce the lifespan of the battery.
The resistance 10 kΩ determines the current through the LED. In this case, one can assume that about
2V are applied to the LED, thus another 7V at the resistor. The result is a current of only 0.7mA. For
comparison: LEDs are mostly designed for currents of 20mA. This red LED, however, begins to generate
significantly visible light even with less than 1 mA.
3 Plug design
Open the third door and take a breadboard out of the compartment. This device makes it easier to
design complicated circuits. The breadboard, with a total of 270 contacts in the 2.54-mm grid (0.1 in),
provides a secure connection of the components.
The plug field has 230 contacts in the middle area, each of which is connected conductively through
vertical strips with five contacts. In addition, there are 40 at the edge for the power supply; these
consist of two horizontal contact spring strips with 20 contacts each. The plug field thus has two
independent supply rails, which are used here for the positive and negative terminals of the battery.
Inserting components requires a relatively large amount of strength. The connection wires thus bend
over easily. It is important that the wires be inserted exactly from above. A pair of tweezers or a small
pair of pliers helps in this process. A wire is grasped as short a distance above the breadboard as
possible and pushed downward vertically. In this way, even sensitive connection wires like the tinplated ends of the battery clip can be inserted without bending.
Construct the circuit from the first test yet again on the breadboard. Again, you are building a series
circuit with resistance and LED. The circuit diagram shows the precise circuitry, but with a slightly
different arrangement of the components, which is as similar as possible to the actual test.
4 Lamp switch
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Behind the fourth door, you will find the wire necessary for all following tests. Build an LED lamp with
switch contact. Cut a suitable piece of wire, 4cm in length, and strip the insulation from the ends to a
length of about 5mm. This wire should be installed as connection to the LED. A shorter wire, 2cm
long, is installed as strain relief to protect the weak connection wires. The battery clip should always
remain connected so that the connections do not wear down too much.
The simple switch consists of two bare pieces of wire that touch together only when pushed together
with the finger. For this purpose, cut two pieces of wire, 2 cm long, and remove the insulation
completely.
5 A protective diode
You will find another red LED behind Door Number 5. Install this second LED in the circuit. The
direction must be correct for this; otherwise, no current will flow. If everything has been put together
correctly, both LEDs light up. And although two LEDs are now in series, the brightness of the first LED
remains practically the same.
The new LED has an important function for the following tests. It serves as a protective diode and
should prevent an incorrect polarity of the battery. The component to be installed tomorrow, in
particular, reacts very sensitively to an incorrect polarity and should be protected against potential
faults. At the same time, the LED is a simple current indicator, with which one can recognize the correct
function of a circuit.
6 Digital circuit
Open Door Number 6. Behind it you will find the most important part of this calendar, the CMOS-IC
4060. This IC with 16 pins contains a total of 14 divider flip-flops and a multifaceted oscillator circuit.
The connections 1 and 16 are on the left side and are marked with a groove. An additional note is
offered by the label, which one can read on the lower row (Pin 1 to Pin 8). Before the first use of the IC,
the connections must be aligned to be parallel because they still stand a bit too far to the outside after
the production. Push all pins on one side at the same time on a hard table surface to align them
sufficiently. Then place the IC correctly on the breadboard. Attention: if it is inserted the wrong way
round, the connections 8 (GND, negative) and 16 (VCC, positive) are switched, so that the operating
voltage is connected with the wrong polarity and the IC is destroyed. In this case, even the protective
diode at the positive terminal does not help, since it protects only against a battery that is connected
the wrong way round.
The first test uses a portion of the oscillator circuit at the connections 10 and 11. The input OSC1 is placed at
GND (negative terminal, logical zero). At the output OSC2 is the LED with its series resistor. If everything has
been assembled correctly, the LED lights up. The IC thus has the voltage switched on at the output (logical
one) and thereby inverts the input status. For most of the tests with the 4060, the reset input (RES) must
also be attached at GND. The red LED at the VCC connection indicates the operating current and protects
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the IC. If everything is correct, both LEDs light up with the same brightness.
7 An open input
Open the seventh door and take out a resistor. It has 22 MΩ (22 mega-ohms, red, red, blue) and is
repeatedly used in the following tests in the oscillator circuit. The resistor is connected at the input OSC1
only on one side. One thus has an "open input". It is undefined whether one or zero is present; the LED is
either on or off. The result is random and can be affected by bringing your finger close to it. Even at a
distance of a few centimetres, the status of the gate can change. Static charges and the electrical fields
connected with them are responsible for this change.
You can turn the output on or off by tapping briefly on the input with your finger. If it is switched on, both
LEDs light up; if it is switched off, both LEDs can be off. The IC then consumes virtually no power.
However, there can be circumstances in which the output is indeed still switched off, but the IC
nevertheless consumes a certain amount of power. That is the case when the input voltage is neither
exactly zero nor exactly at the operating voltage but is somehow between these voltages. As long as the
input is touched, a half brightness can also be adjusted, whereby the LEDs actually flash very rapidly.
This lies in the 50-Hz AC fields of the electrical grid, which have the effect that your own body conducts a
small alternating current.
8 Feedback
Behind Door Number 8 you will find a 10 kΩ resistor (brown, black, orange). This time, it is used as
protective resistance at the input of the IC. The 22-MΩ resistor connects the second output to the input of
the oscillator circuit. The LED is either on or off; the result is unpredictable. An existing status lasts for a
random length of time. You can change the status, however, if you hold the free connection at the input
once at the positive and once at the negative. Beyond that, you can with some luck switch the LED on or
off if you simply tap the resistor with your finger or touch it with a piece of wire that you hold in your
hand.
In this circuit, two inverters are placed in series. An input zero state becomes a one state after the first
inverter and goes back to zero after the second inverter. Through the feedback, therefore, the zero state
is maintained at the input as well. Conversely, a one status at the output appears as one again and
persists. However, if the input is brought to the other state even very briefly, the circuit turns over. A
random impulse often suffices for this purpose, which occurs when you touch it because you are
electrically charged.This kind of circuit is also called a trigger circuit or a flip-flop. At the same time,
therefore, the circuit is also a digital memory with a storage size of 1 bit. If you take the right LED at the
output OSC3 out of the circuit, the circuit is practically de-energized even in the one state. The left LED
is thus permanently off regardless. Only in the switch-over moment does current flow. If you touch the
input, the left LED can light up.
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9 An LED flasher
Behind the ninth door, you will find a ceramic disk capacitor with the capacity 100 nF. The label reads
104 and stands for 100,000 pF (picofarads), thus 100 nF (nanofarads). The capacitor allows you to build
an oscillator, that is, a circuit that automatically switches the state repeatedly. In this case, a slow
flashing light occurs. This time, the high-ohmic resistor with 22MΩ lies between OSC1 and OSC2 and
forms a negative feedback. The 10 kΩ resistor, together with the 100nF capacitor, forms the feedback.
The speed of the switch-over is determined primarily by the 100nF capacitor and the 22MΩ resistor.
Both components together have a time constant of 0.1µF*22MΩ = 2.2s. And in fact, each stable state
lasts about two seconds. In one minute, therefore, the output is on approximately 15 times and off 15
times. If you touch both connections of the 22-MΩ resistor with your finger, you connect your body's
resistance in the scale of 1MΩ in parallel and thereby reduce the time constant. The more firmly you
hold onto the wires, the faster the flashing will be.
At the protective LED, one can see that current begins to flow in each case even before the switch-over
into the on state. This is a sign that medium voltages are present at the input. Even if you remove the
right LED from the output, you can see the regular increase of the current.
10 Fast flickering
Behind Door Number 10 you will find a 100kΩ resistor (brown, black, yellow). It should now replace
the previous 22MΩ resistor in the oscillator circuit. The flashing thus becomes so fast that it appears to
be a steady light. However, if you move the entire circuit back and forth, you will see lighted stretches
with interruptions. One can achieve the same effect by observing the layout in a moving mirror.
This time, the time constant is 100kΩ*100nF = 10ms. The output is on for 10 ms and off for 10 ms.
The result is a total period of 20 ms and a frequency of 50Hz, thus in the scale of the mains
frequency.One can still recognize up to 16Hz as flickering. Above that, one mostly sees only a steady
light.
11 Divider through 16
A 10 nF capacitor (labelled 103) is hiding behind the eleventh door. It receives an auxiliary function and
lies between the positive and negative terminals of the battery. This is a standard measure in all digital
circuits and helps to avoid transient signals. The oscillator is converted back to a low frequency, and
the second LED is now connected to a series resistor at the output Q4. The LED switches between
roughly 30 s on and 30 s off.
Differently from before, the IC now connects directly to the battery. Because everything has functioned
properly so far, you can now take a chance on experimenting even without polarity protection. The
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second LED is thus free for the actual test and shows the distributed frequency. Between the oscillator
and Q4, there are four divider steps that divide the frequency of the clock signal respectively by two.
Thus, 16 clock pulses add up to one output impulse. The elementary period is four seconds at the
oscillator and about one minute at the output Q4.
12 Counter from zero to three
Behind the twelfth door is another 10kΩ resistor (brown, black, orange), which is placed in the
oscillator. The frequency is indeed increased again to around 50Hz, but this time an LED is placed at
the output Q5, which divides the clock signal by 32. At the two LEDs, one therefore sees one faster and
one slower flashing. Both signals together can be read as a 2-bit binary number.
The counter thus constantly counts from zero to three. Then it runs over and continues with zero.
Observed more closely, the LEDs display multiples of 8, that is, 0, 8, 16, and 24 input pulses of the
oscillator. The first three divider steps act as pre-scaler by 8 and deliver a clock signal of around 6 Hz,
which can still be easily followed with the eye. If you would like to see the counter more slowly, you
can insert the 22-MΩ resistor in the circuit. The counter state then switches roughly in the period of
half-minutes, so that one has built a simple digital clock.
13 Three-bit counter to seven
Behind Door Number 13 you will find a yellow LED. With this addition, the counter should be expanded
to three bits. There are now a total of eight different counter states between 000 (zero) and 111 (seven).
The two red LEDs at the outputs Q5 and Q6 share a joint series resistor. The flashing with the lowest
frequency occurs at Q6.
A resistance for two LEDs is possible but leads to a special effect. The red LED at Q6 displays two
brightness levels. As long as Q5 and Q6 are switched on, the current distributes itself through the series
resistor to two LEDs. In the first tests, relatively high LED series resistors of 10 kΩ were deliberately
used. One thereby achieves only an adequate brightness and can experiment without being blinded.
Plus, this circuitry saves energy so that the battery will last as long as possible to the end of the testing.
14 Three-four time
Behind the 14th door you will find another 10 kΩ resistor (brown, black, orange). It is now installed
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between VCC and RES. In addition, two LEDs are placed from Q5 and Q6 to the reset input. But watch
out: this time the cathodes are placed at the outputs. The result is a very special blinker that takes on
three states – flashing in three-four time!
Until now, input pulses could be divided only by two. Divisor ratios of 16, 32, 64, etc. are thus possible, up
to a maximum of 16,384 at output Q14. But when one uses the reset input and additional diodes, almost
any divisor you desire can be achieved. A resistor attempts to increase the reset input. But the connected
diodes keep the voltage low as long as at least one of the outputs used is at zero. In this case, the counter
runs until Q5 and Q6 are switched on. Then a reset occurs immediately, and the counter is reset to zero.
For the two outputs, that means that only possible states occur: 00, 01 and 10. Thus a divisor by three
arises. With this method, you can also achieve almost any divisor ratios you desire. With two diodes, for
example, you can create a divisor by 5 or by 9.
15 Stopped counter
The 15th door reveals a push-button switch. Pay attention to the installation direction. The switch
contact always lies between two adjacent pins. The button is now used to stop the oscillator. A counter
with three outputs recognizes eight different states. The task now is to stop the counter always exactly
in the moment when all three LEDs are on.
This time the smaller 10 nF capacitor is used in the oscillator. The frequency is thus ten times higher and
the task is correspondingly harder. When closed, the push-button switch applies the full operating voltage
to the oscillator input and thereby prevents further oscillations. As soon as the contact is opened, the
oscillator starts again.
16 High-speed dice
Behind Door Number 16 you will find a 4.7kΩ resistor (yellow, violet, red). The oscillator is now converted
again and should be so fast that one can no longer distinguish the individual flash pattern. The result is then
truly random chance – as with an actual die. When one presses the button, the die stops in one of eight
possible states. Differently from an actual die, the states 000 (zero) and 111 (seven) must not be counted. All
other results stand for the numbers 1 to 6. In rolling the die, therefore, one can also learn the binary counting
system at the same time:
1=001b, 2=010b, 3=011b, 4=100b, 5=101b, 6=110b
An oscillator without the capacitor, that may be puzzling at first. Actually, however, there is a very small
capacitor present. Two adjacent contact strips of the breadboard form a capacitor with about 4 pF (4
picofarads). With the 22MΩ resistor, the result is thereby a pulse frequency of about 5kHz. At Q6, the
frequency, divided by 64, appears at around 80Hz. The human eye can no longer follow this fast change.
The oscillator becomes even faster with a resistance of 100kΩ. It oscillates then at around 600kHz and
has a marked effect even on a nearby medium-wave radio. The oscillator of the CD4060 functions with
the components of the calendar in a vast range between 0.25 Hz and 600 kHz. In addition, you can
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usually generate a precise 50-Hz cycle by directly touching the input. In this test, the result is that the
blink pattern is run through significantly more slowly.
17 Light sensor
Another yellow LED is hiding behind Door Number 17. Both yellow LEDs together should now form a
light sensor. If a lot of light falls on the yellow LEDs, one receives a fast flickering of the red LEDs. In the
dark, the flashing becomes very slow.
The oscillator works again with the extremely small capacitor of two contacts of the breadboard. Thus,
even with a high resistance of 22 MΩ, a high frequency results. The two yellow LEDs form a resistor that
is much higher still, however, yet one that is dependent on the ambient brightness. Both LEDs are
connected in series such that one of the two always operates in the back direction. Thus, there should
actually not be any current flowing. However, when light falls on the LED crystal, the LED acts like a
photodiode. Now a small amount of current flows even in the back direction. The more light falls on the
LEDs, the larger this current is, and the higher the oscillator frequency becomes.
18 Button counter
Behind the 18th door you will find a 4.7kΩ resistor (yellow, violet, red). With it, another LED can now
be operated with greater brightness. In all, four LEDs create four bits of a binary number. Therefore, 16
numbers between 0 and 15 can be represented. But this time the counter does not run by itself;
instead, the pulse is generated by the push-button switch.
After every eight button presses, a level change should be observable at Q4. Actually, however, the
change is significantly more frequent. In most cases, it takes three or four button presses for a change
at the outputs. This is due to the contact bounce of the switch, where the contacts bounce back
multiple times on closing. Thus, with one push, one generates a short series of impulses, which are all
counted.
19 Debouncing the button
Door Number 19 reveals a 2.2kΩ resistor (red, red, red). With it, you have a further resistor for a
greater brightness. The significant change to the test consists in an additional capacitor parallel to the
input OSC1. It serves to debounce the button. Thus, with each button press, exactly one pulse is now
counted. After every eight pulses, the output Q4 changes. And after every 128 pulses, the counter
returns to its starting state. One thus has an reliable event counter.
The 4060 can count pulses that are shorter than one microsecond. The 100nF capacitor, together with
the 10kΩ resistor, has a time constant of one millisecond, which is a thousand times longer. That is
thus how long it takes for the capacitor to discharge after the contact opens. However, since the contact
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bounce is significantly faster, the counter always recognizes only one pulse. This reliable 4-bit counter
can also represent larger numbers if one uses the higher-valued outputs. In all, it takes 16,384 button
presses for all outputs, including Q14, to return to their starting state.
20 Multi-flash pattern
Open Door Number 20 and take out a 1kΩ resistor (brown, black, red). With it, you have the series
resistor suitable for maximum brightness. This time, very special flash patterns should result. Each of
the yellow LEDs flashes four times in a row and then pauses while the other LED flashes. The two red
LEDs each flash once and then pause longer.
The special flash pattern occurs because the LEDs conduct current in only one direction. The lower
yellow LED lights up only when Q7 is already switched off and Q4 is already on. Thus, one can create
very different patterns with LEDs at additional outputs. At any rate, it is permitted in this case to
connect LEDs even without resistors directly between two outputs. At an operating voltage of 9 V, the
output transistors of the 4060 have an on resistance of about 300Ω. Thus, both outputs together have
a resistance of 600Ω. The result is an LED current of around 10mA, which is still significantly below
the permitted 20mA.
21 Four brightness levels
You will find an especially bright green LED behind Door Number 21. In this test, it should become
brighter by stages. There are four brightness levels, 0, 1, 2 and 3, which run in sequence. The red LED
shows the pulse at the same time.
The circuit corresponds in function to a digital-analogue converter, which converts digital numbers into
analogue voltages or currents. Q7 switches a large current through the 1-kΩ resistor on and off. A large
brightness level results. In addition, Q6 switches a smaller current through the 2.2-kΩ resistor on and
off, which adds to the larger current. The result is thus a total of four brightness levels.
22 Colour flasher
Behind Door Number 22, a 100µF (microfarad) electrolytic capacitor appears. It has a thousand times
greater capacity than the 100 nF disk capacitor you have used up to now. One thus achieves large
charging currents that can be seen as LED light flashes. Here green and yellow light flashes occur in a
longer interval. Each flash gradually subsides in about half a second. So that one does not have to wait
too long for the flashes, the smaller 10 nF capacitor is installed in the oscillator. The red LED shows the
divided pulse signal.
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When using an electrolytic capacitor, the installation direction must be observed. The negative terminal
is marked with a white stripe. If one applies a current to the electrolytic capacitor the wrong way round
for a long time, it can be destroyed and in the worst case even burst. Here the positive terminal is
placed at Q12, where the voltage is alternately +9V and 0V. Two LEDs must be connected in the back
direction so that the electrolytic capacitor can alternately charge and discharge.
23 Four-way flashing light
Behind the 23rd door you will find a white LED. Four LEDs should now flash in sequence such that two
LEDs are never on at the same time. Despite that, only two counter outputs are used for this test. The
outputs Q12 and Q13 generate very slow changes. So that it does not take too long, the oscillator is
again set to a higher clock frequency with the smaller 10 nF capacitor.
The circuit forms a 1-of-4 decoder, which decodes single states from four possible binary numbers at
two outputs. Normally, one needs additional logical circuits for this purpose, but none are available
here. The circuit functions only with a trick and relies on the fact that the different LEDs operate at
different voltages. The red LEDs light up with less than 1.8 V; by contrast, the green and the white LED
require significantly more than 2V. When Q13 is switched on, the 10-kΩ series resistor supplies power
for the green LED. However, if Q12 is in the zero state at the same time, the red LED is practically
parallel to the green LED and draws current away from it because of the lower LED voltage. Q12 thus
determines whether the green or the lower red LED lights up. In the one state of Q13, by contrast, either
the white or the upper red LED lights.
24 Firelight and falling stars
Behind the last door you will find another 1kΩ resistor (brown, black, red). It is used for a festive light
that can be used to decorate the Christmas tree at the end of the experiments. Two red and two yellow
LEDs stand for a wood fire, which generates a relatively constant light and flickers only slightly.
Sometimes, however, a falling star lights up the night for a brief moment, represented by a green or a
white LED.
The base brightness of the red and yellow LEDs is predetermined by two 1kΩ resistors. Larger resistors
with 4.7kΩ and 10kΩ switch smaller currents from various counter outputs to the LEDs and provide
for a slight and seemingly irregular flickering. It has a calming effect and is also nice to look at for a
long time. The infrequently occurring light flashes are generated with output Q10 and a 100µF
electrolytic capacitor. It is easy to make changes. Experiment with other counter outputs and different
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resistors and make a Christmas light that is entirely your own.
Appendix
Components in the calendar:
1 red LED + 10 kΩ resistor
2 Battery clip
3 Breadboard
4 Wire
5 Red LED
6 CD4060
7 22 MΩ resistor
8 10 kΩ resistor
9 100 nF capacitor
10 100 kΩ resistor
11 10 nF capacitor
12 10 kΩ resistor
13 Yellow LED
14 10 kΩ resistor
15 Push-button switch
16 4.7 kΩ resistor
17 Yellow LED
18 4.7 kΩ resistor
19 2.2 kΩ resistor
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20 1 kΩ resistor
21 Green LED
22 100 µF electrolytic capacitor
23 White LED
24 1 kΩ resistor
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