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During construction it should be remembered that the full mains voltage may appear across any point in the circuit. As- R2 suming, for simplicity, that the mixer is dealing with AC input signals, under quiescent no sig- nal conditions the DC current through R2 is al- most entirely supplied by T1 and is almost equal to the collector current.
The output of Nl will thus go high and the output of N2 low, which will hold the inputs of Nl low even after the finger has elektro removed. When making measurements where the signal level varies, for example at different places in a circuit, it is tedious to have to make frequent adjustments to this control.
The output from the temperature sensor in the iron is con- nected to the eletkor input and compared with a reference voltage at the non-inverting input, set by PI. The circuit consists basically of a peak rectifier that provides one input of a comparator with a DC voltage equal to a fixed percentage of the peak signal level.
The voltage drop across Cl thus increases lin- early, so the output voltage of Nl falls linearly until the lower threshold voltage of the Schmitt trigger is reached, when the output of the Schmitt trigger goes low. The circuit consumes very little current 0. Once the output voltage of the supply has risen to its elekotr value D7 is reverse-biased, which prevents ripple from the unregulated supply appearing on the output. Long interval timer The drawback of most analogue timers mono- stable circuits is that, in order to obtain reason- ably long intervals, the RC time constant must be correspondingly large.
Elektor – 301 Circuits.pdf
This is done by decreasing the value of R7. If one of the lamps fails, then the current through the operating coil falls to about half, causing the relay ele,tor drop out and the LED on the dashboard to be extinguished. When current is drawn from the dlektor, the right-hand end of the shunt will be at a lower potential than the left-hand end, so the output of Al will rise, and the discharge indicating LEDs D5 to D8 will light successively as the current increases.
The supply basically consists of an amplifier with a gain of 2, comprising a op-amp and an emitter follower, T2, to boost the output current capability. PI adjusts the trigger point of the Schmitt trigger, which varies the duty-cycle of the squarewave and elektog the sinewave purity.
Although it is in fact available, the crystal 2.
Construction No trouble is to be anticipated if the circuit is built up using the PC board layout given in eleotor ure 2. Two points must be noted when using this eelktor cuit.
As a glance at the circuit diagram makes clear, the circuit is ideally suited for miniaturisation; as e,ektor mentioned, the current consumption is so small as to be negligible. In view of the dramatic drop in the price of crys- 2 tals used in colour TV sets, they now represent an economical way of building an SSB-filter. This invariably means resistor values in excess of I MO, which can give timing errors due to stray leakage resistance in the circuit, or large electrolytic capacitors, which again can introduce timing errors due to their leakage resistance.
Figure la shows the basic circuit, which uses three of the gates in a quad two-input NAND buffer IC, N1 and N2 are connected as a 20 kHz astable multivibrator, and the output of N2 drives N3, which acts as a buffer between the astable and the doubler circuit. When the voltage on C2 equals that at the non- inverting input the output of IC1 goes low. The circuit of the logic tester is shown in figure 1Three voltage comparators are used to detect the four possible input conditions.
P2 is then ad- justed until clock noise is at a minimum.
A suggested printed circuit board design and component elsktor for the cir- cuit of figure 2. An additional bonus is that the alarm will also sound in the event of a lamp filament failure. The circuit consists simply of a timer con- nected as a 1 kHz astable multivibrator. The switching circuit is shown in figure 1. Depending upon the logic level of the input signal, one of the above frequencies is fed to the output. The output waveform of IC1 thus consists of a series of positive pulses whose duration T2 is a constant and whose spacing Tl depends on the output elektkr of IC2.
The solid-state voltmeter described in this article allows continuous monitoring of the battery voltage so that incipient failure can be spotted at an early stage.
Improved supply Square wave-staircase converter When the voltage across Cl reaches the thres- hold value of NlT3 is turned on via NJ and N2 S and Cl is discharged, after which the whole cycle repeats itself.
The reverse characteristic of a zener diode is il- lustrated in figure 1.
Should the output voltage of the regulator tend to fall then the lower end of D 5 will fall below 0 V and transistor T3 will draw more current. The theoretical currents for the various combinations of SI, S2 and S3.
Elektor – 301 Circuits
The miniature ultrasonic transmitter which is concealed on the person of the user consists rlektor a handful of components, and the current con- sumption is negligible approx. The exact formula is given in the diagram. A constant current of – thus flows through R2. The result is a piercing 3 kHz signal which is made audible via an 8 ohm miniature loudspeaker or earpiece insert.
An initial bias of about 10 V from the unregulated supply is provided by these components. If the output is not elektir 0.
Full text of “Elektor – Circuits”
However, with supply voltages greater than 10 V this should not be a problem. Cl now charges from the output of ICl via R4 until the voltage across it exceeds the voltage at the non-inverting input, when the output of ICl,t. At each zero-crossing of the sinewave the Schmitt trigger changes state, thus producing the original squarewave that is fed to the input of IC2. When the output of N3 goes high the voltage on the positive end of O is about 9 V, so Cl discharges through D2 into C2.
With the component values given in the diagram the circuit consumes mA with a 5 V stabil- ised supply. The average voltage fed to the series transistor will thus be less than 8.