Due to the low duty cycle of flashing LED, the average current drain is 1 mA or less. The NE555 will trigger the LED on when the monitored voltage falls to 12 volts..
This field strength meter consists of a tuned crystal detector producing a dc output voltage from a transmitted signal. The dc voltage is used to shift the frequency of a transmitter of 100-mW power operating at 1650 kHz. The frequency shift is proportional to the received field strength...
This circuit has a flat response from 8Hz to 50 kHz at -3 db on tbe 10-mV range. ..
A high-gain amplifier using a UA741 is used to sense relative voltage drop in a conductor, and therefore current i..
These two comparators are over- and under-voltage comparators. In Fig. 104-5(a), if Vm exceeds the reference voltage, t..
The circuit consists of two basic circuits, the oscillator and the detector. The oscillator uses an FET in a Colpitts configuration. The energy circulating in the oscillator tank is coupled through C4 to the detector circuit, where a small diode (D2) rectifies it, feeding a dc voltage to the Darlington pair (Q2, A3) controlled by the sensitivity control (R3). Any small variations in the bias of the amplifier will cause large variations of current through the LED indicator.....
This circuit, instead of dividing by an integer, divides the input signal by +1/2. With the feedback connections ..
The circuit is built around a 741 general-purpose op amp that is configured as a voltage follower; with the components shown, the op amp has a voltage gain of one. The output of the 741 is used to drive a 50- meter movement. Potentiometer R7 is used to zero the meter and R6 sets the meter`s full-scale reading, Calibrating the meter is a snap. With no input applied to the circuit, set R6 to mid-position and adjust R7 to zero the meter. Once that is done, apply a positive.....
The first amplifier circuit is a bird phone. In this circuit, the electret mike (MIC1) is mounted in the neck of a large plastic funnel. The amplifier, built around an MC34119 (which is available from D.C. Electronics, P.O. Box 3203, Scottsdale, AZ 85271-3203; Tel. 800-467-7736, and elsewhere), is then placed outside of the funnel with the pickup facing a nearby bird feeder. The output of the amplifier is then connected to a 16- speaker. The amplifier`s voltage gain is.....
A low-cost filament transformer provides a linear indication of the load current in an ac line. ..
The circuit is built around a single 4093 quad 2-input NAND Schmitt trigger...
The telephone-line tester consists of nothing more than a meter (that`s used to measure line voltage in the on- and off-hook state), three resistors (one of which is variable), a pushbutton switch, and a modular telephone connector...
Sounds are picked up by MIC1 and fed to the input of the first op amp. The signal is then fed to the input of second op amp Ulb, where it is boosted again by a factor of between 1 and 33, depending upon the setting of range switch Sl. With the range switch set in the A position, R6 is 1 K!:J and R7 is 33 K!:J, so that stage has a gain of 33. ..
Driving a D/A converter with an A/D converter provides an overall analog-hold function, which though limited in output resolution, offers zero voltage droop and infinite hold time. The A/D converter shown (IC1) includes a 12-bit compatible track/hold at its input. The track/hold specifies a 6-MHz full-power bandwidth, a 30-ns aperture delay, and a 50-ps aperture jitter. ..
The shift pulse turns off the conducting scs by reverse biasing the cathode gate. The charge stored on the coupling capacitor then triggers the next stage. An excessively long shift pulse charges up all the capacitors, turning off all stages. ..
One section of the precision audio frequency generator uses an electret microphone element to pick up audio from the piano. That signal is then processed and sent to one channel of a dual-trace oscilloscope. The other section of the circuit is used to produce a variable-frequency signal that is fed to a digital frequency counter...
If the tube is level with respect to gravity, the bubble resides in the tube"s center and the electrode resistances to common are identical. As the tube shifts away from level, the resistances increase and decrease proportionally. Transducers of this type must be excited with an ac waveform to avoid damage to the partially conductive liquid inside the tube. The level transducer is configured with a pair of 2-KO resistors to form a bridge. The required ac bridge.....
When SI is pressed, counter U2 is driven by oscillator U1A/U1B and the count (0 through 6) is read on DISP1. Rl and CI dete..
One lamp at a time is lit in the string to give the appearance of a moving point of light. ..
This FETVM replaces the function of the VTVM while at the same time ridding the instrument of the usual line cord. In addition, drift rates are far superior to vacuum tube circuits allowing a 0 volt full scale range which is impractical with most vacuum tubes...
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