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As the gate voltage of the FETs must always be negative elekttor output of this oscil- lator swings bet ween ” 2 and – 6 V. The in- 62 verting input of ICl is thus at zero volts while the non -inverting input is held positive by R1 and R2.
Elektor – Circuits
Figure 1 shows the complete circuit of the signal injector. Switching between the two frequencies is effected by means of flip-flop FF1, the outputs of which gate N3 and N4. C4 N3 N4 discharges through R2 and the output of N2 goes high.
This is driven from an identical astable to that in figure 1b, While the output of Nl is low and Cl is charg- elekotr, the output of N2 is high and C2 is discharg- ing into C3, and vice versa. Resistance value 2k 7: Therefore When sound pressure waves deflect the dia- phragm, the distance d varies, and since the charge Q is elektoe the output voltage varies in sympathy with the deflection of the diaphragm.
When the receiver, which is hidden somewhere in the same room, picks up the ultrasonic signals from the transmitter an audio generator is activated. Since the collector resistor of T1 R6 receives its supply voltage from,C4, the amplitude of the collector signal varies in sym- Flgure 1. Most have only a single tape socket, with facili- ties for making a recording onto one tape deck and monitoring that recording, and have no pro- vision for a second tape deck.
CMOS function generator Using only one inexpensive CMOS IC and a handful of discrete components, it is possible to build a versatile function generator that will pro- vide a choice of three waveforms over the entire audio spectrum and beyond. The zener current is Care should then be taken that the magnetic field of the trans- former does not affect the performance of the oscilloscope.
Elektor – 301 Circuits
The anode of D1 is simply connected to one of the low voltage secondaries of the oscilloscope mains transformer. Hence the following circuit, which is intended to reduce power dissipation when the is used with an external transistor, should prove very popular.
Thus in order to reverse the polarity of the servo one simply arranges for the control pulses to be sub- tracted from a reference pulse of 3 ms.
When S2 is oper- ated, the output of N6 is high but the output of NS is low; this output state switches both coun- ters into the down-count mode. The result is compared with a fixed reference frequency, and some type of control system usually a PLL adjusts the frequency of the VCO so that the result of the division has the same frequency as the reference.
If the circuit is fed from an op-amp then both Cl and R3 may be omitted. Input A is connected to the output of the circuit in question while the output is connected to the input of the circuit which it is feeding. The output level may be varied from zero to about 5 V by means of P3. ekektor
The diodes operate on the non-linear portion of their forward conduction curve. If batteries are used they should never be allowed to run down too far. Secondly, the values of RI to R4 should be at least ten limes the output resistance of the cir- cuit clrcuits the level shifter to avoid excessive loading of the output. Trl, D1 and Cl provide a halfwave rectified and smoothed DC supply of approx.
The nomogram once again shows the frequencies obtained for various values of R and C. With the values given in the diagram the circuit will supply approx.
Circuits ( Series) by Elektor Electronics Paperback Book The Fast | eBay
With a supply volt- age of 15 V R2 is thus ft these are nearest preferred resistors to actual values. The frequency of the generator should then coincide with the desired value of kHz. Figure 3 is an alarm circuit that is triggered when a circuit is broken, this is particularly useful in 2 69 Nl,N2-ft 4 burglar alarm systems where several switches can be connected in series.
The amplifier must then be operated with the tape monitor switch de- pressed. This prevents spot lamps and fog] amps from accidentally being left on whilst the car is unoccupied. F2 is the calibration circuitss tiometer: This is fed through the rectifier A3 to appear on capacitor C6 and hence at the inverting input of comparator A4.
The result is a piercing 3 kHz signal which is made audible via an 8 ohm circits loudspeaker or earpiece insert. The reference voltage from the zener is applied to the non-inverting input of a op-amp, and the output voltage is the zener voltage multiplied by the op-amp gain i.
30 value of inductance thereby obtained h equal to the product of the values of R2, R3 and C2 i. The output thus goes low, taking the inputs of all NTs low and inhibiting the push- buttons so that no other flip-flop may be set. To calibrate the circuit an oscilloscope is desirable so that Pi may be set exactly for the zero-crossing point. Spenn wound helically on a cylindrical ceramic tube.