Table of Contents Table of Contents 3 1 Introduction 1.1 Plug-in field 1.2 Battery 1.3 Light-emitting diodes 1.4 Resistors 1.5 Capacitors 1.6 Scanning switch 1.7 Fourfold NAND-Gate 4011 1.
11 Variable Frequency 44 12 Frequency Divider 46 13 Divider by Four 49 14 Stop and Go 52 15 Set and Reset 55 16 JK-Flipflop 58 17 Slide Register 61 18 Phase Offset 90 Degrees 64 19 Bit Decoder 67 20 One of Four 69 21 Synchronous Counter 71 4
1 Introduction Digital electronics is the basis of state-of-the-art computer technology. "Digital" means that there are only clear on and off conditions in the circuit, but no interim conditions like half on or three quarters on, as known from analogue electronics. Therefore, there are fewer options on first glance. If you use many digital lines at once, there is a great many different conditions. Every single condition is referred to as a bit.
overview in the photographs. However, use the connection wires unshortened so that they can still be used for further experiments. 1.1 Plug-in field All experiments are set up on a lab experimenting board. The plug-in field with a total of 270 contacts in a 2.54 mm grid ensures safe connections of the components. Fig. 1: The experimenting field The pinboard field has 230 contacts in the centre area, each of which are connected conductively to five contacts with vertical strips each.
connections. You can see the short contact series in the centre field and the long supply rails at the edge. Fig. 2: The internal contact rows Insertion of components requires relatively high power. The connection wires therefore bend easily.
precisely from the top. Tweezers or small pliers will help with this. A wire is held as close to the pinboard as possible and pushed vertically down. This permits insertion of even sensitive connection wires like the tin-plated ends of the battery clip. For the test, you need short and longer wire pieces that you need to cut to match the included circuit wire. To strip the wire ends, the insulation can be cut with a sharp knife all around. 1.
Fig. 3: The battery, real and as circuit symbol Do not use any alkaline batteries or rechargeable batteries, but only simple zinc carbon batteries. The alkaline battery may have a longer service life, but it has a big disadvantage: Like a rechargeable battery, it delivery very high currents of up to more than 5 A in case of error, which will strongly heat think wires or the battery itself.
current of a zinc carbon block battery, in contrast, is usually less than 1 A. This may already destroy sensitive components, but there is no danger of burns. The included battery clip has a connection cable with flexible strand. The cable ends are stripped and tin-plated. This makes them stiff enough to plug them into the contacts of the pinboard. However, frequent plugging may cause them to lose their shape.
Fig. 4: The light emitter diode 1.4 Resistors The resistors in the learning package are carbon-layer resistors with tolerances of ±5 %. The resistor material is applied to a ceramics rod and coated in a protective layer. It is labelled in the form of coloured rings. In addition to the impedance, the accuracy class is indicated as well.
Fig. 5: A resistor Resistors with a tolerance of ±5 % are available at the values of the E24-series, with each decade containing 24 values with about equal distance to the adjacent value.
The colour code is read from the ring closer to the edge of the resistor. The first two rings represent two digits, the third the multiplier of the impedance value in Ohm (Ω). A fourth ring indicates the tolerance. Table 2: The resistor colour code Colour Ring 1 1st number Black Ring 2 Ring 3 2nd number Multiplier 0 1 Ring 4 Tolerance Brown 1 1 10 1% Red 2 2 100 2% Orange 3 3 1.000 Yellow 4 4 10.000 Green 5 5 100.000 Blue 6 6 1.000.000 Violet 7 7 10.000.
1.5 Capacitors A capacitor comprises two metal surfaces and an insulation layer. Applying electrical voltage will lead to formation of an electrical force field between the capacitor plates, in which energy is stored. The capacity of a capacitor is measured in farad (F). The insulating material (dielectric) increases capacity as compared to air insulation. Ceramics disc capacitors use a special ceramics material with which high capacities are reached at small builds.
Fig. 6: A ceramics capacitor 1.6 Scanning switch The pushbuttons in the learning package have a normally open contact with two connections, each of which is performed double. Fig.
1.7 Fourfold NAND-Gate 4011 An integrated circuit (IC) contains many components in one casing. The 4011 is a CMOS-IC with four NAND-gates. The IC is protected well against electrostatic discharge and does not need to be treated with any special care. Make sure that the operating voltage is connected in the correct direction. If you install the IC in the wrong direction, it will heat up too much and be destroyed. When first inserting into the pinboard, the 14 connection legs must be aligned in parallel.
the operating voltage is important. The operating voltage in all ICs of the 40xx series may be between 3 V and 15 V. Fig. 9: The CMOS-IC 4027 2 Inverter The CMOS-IC 4011 contains four independent NAND-gates with two inputs each. An initial attempt shows use of the IC at a battery voltage of 9 V and connection of LEDs. When installing, always observe correct polarity. The plus connection is also called Vcc, the minus connection GND.
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Fig. 11: Pinboard setup The circuit uses only two of the four NAND gates (NAND 1 and NAND 4). Both inputs are connected. This turns the NAND gate into an inverter. An input condition zero is turned to an output condition one and vice versa. At the output, one LED each is connected with its dropping resistor. During this experiment, the left LED is lit while the right LED remains off.
Fig. 12: An NAND gate as inverter The function of the circuit can be presented by a so-called truth table. In the lower gate (NAND 1), the input is applied to GND (0), the output is switched on because of this (1). In the upper gate (NAND 4), the input is applied to Vcc (1), the output is switched off because of this (0).
Input Output 0 1 1 0 3 Contact Switch This experiment uses a gate as inverter with open input. The input receives a protective impedance of 100 kΩ and may be touched with the finger. If they are strongly charged electrically, the protective resistance limits the discharge current. The output condition of this circuit cannot be pre-determined, since the input has an extremely high impedance and may carry accidental charge. If the input voltage is clearly above half the operating voltage (4.
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Fig. 14: Setup with touch contact 4 NAND Basic Function In this experiment, the actual function of the NAND gate is examined. This is an AND function with subsequent inverter. The following applies for the AND function: Only when input 1 AND input 2 are on will the output be on as well. Accordingly, the NAND function means that: Only when input 1 AND input 2 are or will the output be off as well. This is also shown in the truth table of the NAND gate.
Input 1 Input 2 Output 0 0 1 0 1 1 1 0 1 1 1 0 Fig. 15: Connections of a NAND gate The circuit uses two resistors with 100 kΩ to achieve the quiescent state zero.
each. In this case, the orange LED is lit in the quiescent state. Oily when both buttons are pushed at once will it go off. Fig.
Fig. 17: Pushbutton setup 5 AND-Gate A subsequent inverter can turn the NAND gate into an AND circuit. This time, the rule is: Only if both switches are shut will the LED be on.
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Fig. 20: Setup of the AND circuit 6 OR-Gate Inverting the two inputs of the NAND gate first leads to an OR gate. The OR function is: When input 1 OR input 2 OR both of them are on will the output be on.
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0 1 1 1 0 1 1 1 1 Fig.
Fig. 23: Testing the OR circuit 7 NOR-Gate Another inverter behind the OR gate generates a not-or function (NOR). To generate a NOR gate, all four NAND gates in the 4011 are needed.
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Fig. 26: Testing the NOR circuit 8 RS-Flipflop A flipflop is a circuit that independently maintains one of two conditions. A digital condition can be saved. Certain input conditions switch the output. The RS flipflop has two inputs, reset (R) and set (S). In the quiescent state, both inputs are set high (R = 1, S = 1). The output is then not determined (X) and depends on the previous history. Switching R to 0 switches the output off. Switching S to zero switches it on.
Input 1 Input 2 Output 0 0 1 0 1 1 1 0 0 1 1 x The RS flipflop can be set up from two NAND gates, with the outputs each being fed back to an input of the other gate. The feedback leads to a condition once present being retained.
Fig. 27: Basic principle of the RS flipflop In the actually set up circuit, both outputs are put to LEDs. At the output of NAND 2, the inverted condition of NAND 1 appears at all times. Two resistors against Vcc ensure quiescent state 1. The pushbuttons can force a 0-condition and therefore change the output condition. When switching on the operating voltage, one of the two LEDs lights up — it is not possible to tell in advance, which one. Both buttons can be used to switch between the two conditions then.
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Fig. 29: Setup with R- and S-button 9 Flash Circuit Two NAND gates, two resistors and a capacitor can be used to build an astable flipflop that independently switches back and forth. Like am RS flipflop, a feedback is used here. A condition is, however, only stable for as long as the capacitor is being charged. Then the starting condition changes. Strictly speaking, this is not a digital circuit because the input voltage of the left gate changes slowly.
Fig. 30: Astable flipflop In the practical circuit, both NAND gates were applied with LEDs that therefore clash alternatingly. The resistors and the capacitor are selected so that a well-visible flashing at a frequency of approx.
results. The circuit presented here is also used as a cycle source for more complex digital circuits below. Fig.
Fig. 32: Setup of the alternating flash 10 Double Flash Four gates can be used to set up two independent flash circuits at once. In theory, they are supposed to work at the same frequency. In practice, however, low component tolerances cause the two circuits to not work perfectly synchronously. If you touch one of the capacitors with your finger, slight heating will cause slight reduction of capacity. The corresponding flash then speeds up a little.
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Fig. 34: Independent flash cycle 11 Variable Frequency The frequency of the two flashers can be varied within wide thresholds if an external resistor is switched in parallel to the 2.2-MΩ resistor in the circuit. The skin impedance is used here. Slight contact of the two wire ends leads to increase of frequency. The oscillators can be used to compare the skin impedances of two persons.
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Fig. 36: Setup with finger contacts 12 Frequency Divider The CMUS-IC 4027 contains two independent JK flipflops. A JK flipflop is a relatively complex and highly diverse circuit. The first test uses the IC as toggle flipflop. The inputs R and S must be applied to GND for this, the inputs J and K to Vcc. »Toggle« means switching. The output state changes at every 0-1 condition change at the cycle input (Clock, C), i..e at every positive cycle flank.
Fig. 37: The JK flipflop as toggle flipflop Circuits with flipflops are sensitive to interference signals. A capacitor between Vcc and GND prevents inferences that may spread across the supply lines. For high reliability of the circuits, an additional resistor of 10 kΩ is inserted in the cycle line.
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This experiment shows both the cycle signal and the output signal of the flipflop using LED. You can clearly see that the output state only changes at half the speed of the cycle signal. Fig. 39: Display of basic frequency and half the frequency 13 Divider by Four Two toggle flipflops can be switched in series. The Q output of the first flipflop controls the C-input of the second flipflop. All in all, the input frequency is divided by four.
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0 0 0 0 At the same time, the circuit can also be seen as a counter if the output states are considered bits of a digital figure. The state at output 1 then has to be on the right. This results in the binary figures 00, 11, 10, 01, 00. The circuit counts backwards: 0, 3, 2, 1, 0 etc. This is because the clock input reacts to the positive flank. Fig..
Fig. 42: Setup of the binary counter This circuit of toggle flipflops in sequence is also referred to as an asynchronous counter or ripple counter. The respective next stage will only switch with a delay of some nano seconds, which is not visible to the eye. 14 Stop and Go Use two open-ended wires instead of the 10 kΩ resistor. The Rx resistor is then formed, e.g., by touch. Switch the cycle signal on and off by touching with your finger. You may let the counter run and stop it by this.
output flickers well visible at 12.5 Hz. This circuit can be used as random number generator like a dice. The two LEDs show the binary number thrown.
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Fig. 44: Counter with touch contacts 15 Set and Reset The inputs R and S can be used as for a RS flipflop. They are operated with two switches here. Additionally, the inputs are applied with impedances against GND that determine the quiescent state zero. The first counter stage can be deleted (R) or set (S) as desired now. While one of the buttons is pushed, the counter remains in the corresponding condition. The condition of the second counter stage also will no longer change.
interference resistance, which is also important for some of the following experiments.
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Fig. 46: Button installation 16 JK-Flipflop The JK flipflop derives its name from the inputs J and K. They are now examined in more detail. Connect the two pushbuttons with the associated resistors to the inputs J and K of the upper flipflop. Use the applied cycle to test all conditions of J and K. One function is already known from the previous tests: With J = 1 and K = 1, the output toggles at every positive cycle flank. Now also try out the other states.
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Fig. 49: Buttons at J and K 17 Slide Register A slide register pushes input conditions one stage forward at every cycle impulse. The 4027 can be used to set up two stages. The cycle signal is now applied in parallel to both clock inputs. The input has two buttons at J and K again. The connection to the next stage is decisive. Q leads to J and /Q to K. In case of a positive cycle flank, the first flipflop assumes the unequal conditions at J and K.
Fig. 50: JK flipflop as slide register In the quiescent state, both inputs J and K are zero. Push the button J now. The 1 condition is assumed at Q1 at the next cycle impulse, and by the following one at Q2 as well. You can clearly see the delay by one cycle. Release the button. Because both inputs J and K of the first stage are now 0, the output does not change. Both outputs remain on. Now push the button K. Q1 is made 0 at the next cycle impulse, and with a one-cycle delay, so is Q2.
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Fig. 52: Experiment setup slide register 18 Phase Offset 90 Degrees Return the output signals of the two-stage slide register to the input. J and K should, however, be swapped. The result is that the first flipflop each take son the inverted condition of the second flipflop. The second one, on contrast, follows the first one as before with a delay on one cycle. All in all, both outputs switch alternatingly.
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Fig. 55: Experiment setup for phase offset Change the circuit once so that J and K are not swapped during feedback. The result is uncertain because it depends on the first condition of the flipflop after switching on. It is possible that both outputs remain permanently on or off, that they change counterphased. 19 Bit Decoder The above experiment had both LEDs lit for two cycles each. Now individual switching phases are decoded and displayed.
outputs have an unequal condition at the time. Since they are switched antiparallel, alternating light phases occur. Output Q2 Output Q1 Numeric value LED 1 LED 2 1 0 2 1 0 1 1 3 0 0 0 1 1 0 1 0 0 0 0 0 Fig.
Fig. 57: Setup with four LEDs 20 One of Four For only one of the four LEDs to be lit at a time, the two LEDs at the right of the circuit diagram must be switched between the two flipflops accordingly. For the two remaining switching phases to be decodable, the lower flipflop's inverted output /Q is used.
0 1 1 0 1 0 0 0 0 0 0 0 1 0 Fig.
Fig. 59: A four LED flash 21 Synchronous Counter A multi-stage synchronous counter generally delivery the same results as a multi-stage ripple counter. The difference is that the outputs now switch precisely at the same time. For this, all stages must work with the same cycle. The cycle signal is now applied in parallel to all Cinputs of the flipflops. A flipflop cannot wait for the result of the previous stage but must know in advance whether it is to switch at the next cycle.
Fig. 60: Synchronous counter principle In the first stage, J and K are connected to Vcc so that a toggle flipflop results. Whenever Q = 1, the following cycle impulse will switch the state. This leads to the correct counting sequence for a binary forward counter.
Fig. 61: Synchronous forward counter Again, four LEDs are to be lit individually in sequence. All in all, a light pattern forms that looks as if a dot circled counter-clockwise.
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Imprint © 2011 Franzis Verlag GmbH, 85586 Poing www.elo-web.de Author: Burkhard Kainka ISBN 978-3-645-10073-1 Produced at the order of Conrad Electronic SE, Klaus-Conrad-Str. 1, 92240 Hirschau All rights reserved, even including photomechanical reproduction and storage on electrical media. Generation and distribution of copies on paper, data carriers or online, in particular as PDF, are only permissible with the express consent of the publisher and will be prosecuted under criminal law.
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