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..
A flashing light of high brightness and short duty cycle is often desired to provide maximum visibility and battery life. This necessitates using an output transistor, which can supply the cold filament surge current of the lamp while maintaining a low saturation voltage. ..
Precise, adjustable control of beats per minute from a largo of 18 to a frenzied, high presto of 500, These beats are produced acoustically through a speaker. A light flashes at the same rate. When SW1 is closed, CI begins to charge through Rl and R2. Cl will eventually reach a voltage at which the emitter of unijunction transistor is switched on, "dumping" the energy stored in Cl into an 8 ohm speaker. To produce a distinct "plop", brief pulses across T2 secondary drive.....
This converter uses a low-pass filter instead of the usual tuned circuit so the only tuning required is with the receiver. The dual-gate MOSFET and FET used in the mixer and oscillator aren"t critical. Any crystal having a frequency compatible with the receiver tuning range may be used. For example, with a 3500 kHz crystal, 3500 kHz on the receiver dial corresponds to zero kHz; 3600 to 100 kHz; 3700 to 200 kHz, etc..
This low-power video transmitter is useful for R/C applications, surveillance, or amateur radio applications. Seven transistors are used in a crystal oscillator-multiplier RF power amplifier chain, and a high-level video modulator. A 9- to 14-Vdc supply is required. ..
The step size of the converter is variable by selection of the high order data bits. The first DAC, A, has a stable reference current supplied via the 10.24 V reference IC and Rl. R2 provides bias cancellation. As shown, only the first 4 MSB inputs are used, giving a step size of 225/256 2.048/16 = 0.127 mA. This current supplies the reference for DAC whose step size is then 0.1275/256 = 0.498 µ. Complementary voltage outputs are available for unipolar output and.....
This circuit has a 100-m V hysteresis which can be used in applications where very fast transition times are required at the output, even though the signal input is very slow. ..
The input signal is amplified by the transistors. The distorted output is then clipped by the two diodes and the high frequency noise is filtered from the circuit via the 500 pF capacitor..
Ql and Q2 constitute a simple, high-speed FET input buffer. Ql functions as a source follower, with the Q2 current source load setting the drain-source channel current. The LT1010 buffer provides output drive capability for cables or whatever load is required. Normally, this open-loop configuration would be quite drifty because there is no de feedback. The LTC1052 contributes this function to stabilize the circuit. It does this by comparing the filtered circuit output.....
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.....
An LM317 voltage regulator is configured as a constant-current source. It is used to supply the 50 mA charging current to S01-S06, an array of AA-cell battery holders. Each of the battery holders is wired in series with an LED and its associated shunt resistor. When the battery holder contains a battery, the LED glows during charging. Each battery holder/LED combination is paralleled by a 5.1-volt Zener diode. If the battery holder is empty, the Zener conducts the current.....
Oscillators that generate a predetermined number of pulses are often required in applications such as video wo..
Integrated circuit Ul (a 555 oscillator/timer) is wired as a conventional pulse generator. The frequency of the pulse generator is controlled by potentiometer Rll. Resistor R2 puts areasonable limit on the highest speed attainable. The output of the pulse generator is fed to the common clock input of U2, a 74C175 quad D-type flip-flop. Each flip-flop is configured so that its Q output is coupled to the D input of the subsequent flip-flop. Information on the D input of.....
This circuit uses a protective resistor R2 in conjunction with feedback resistor Rl. Together, they form a voltage divider to reduce the input voltage amplitude for ICl-a so that the protective diodes never conduct. ..
The incoming RGB inputs are terminated with resistors Rl, R2, and R3 and potentiometers RVl, RV2, and RV3. These provide input impedances of approximately 75 0. The presets should be adjusted to provide a maximum input of 1 V pk-pk into the MC1377. The inputs are ac-coupled into the encoder; the large value capacitor is required for the 60 Hz field component. The Colpitts oscillator for the color burst is formed around pins 17 and 18. About 0.5 V pk-pk should appear.....
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. ..
The circuit uses a dual LED. When power is applied to the probe throughthe power leads, and the input is touched to a low level or ground, Ql is cut off. This will cause Q2 to conduct since the base is positive with respect to the emitter. With Ql cut off and Q2 conducting, the green diode of the dual LED will be forward biased, yielding a green output. Touching the probe tip to a high level will cause Ql and Q2 to complement, and the red diode will be forward biased,.....
Although theIR region is free from radio interference, it is subject to interference from incandescent lamps, fluorescent lamps, stray reflections, and other sources. A simple way to overcome that problem is to create a carrier by chopping the IR radiation at a rate of 100 kHz. The audio then modulates the carrier by modulating the chopping rate. A receiver then detects the IR beam as a 100-kHz FM signal. ..
Have you ever wondered how many different colors can illuminate a LED? One, two or maybe three? Constructing this simple circuit, you will find it much more. The key component in this design is a dual LED. One such accessory includes two inside the 'slices' of different diode LED, that each of them produces a different color (usually green and red). For the drive requires three pins, a common cathode and two separate roots. In this way each of the two integrated diodes can.....
The unit consists of rlamplifier Q1, local oscillatorQ2, and mixer Q3. The two bands are covered without a bandswitch by using an i-f or 3.5 MHz. The oscillator range is 7.5 to 14.5 MHz. Incoming signals from 4 to 11 MHz are mixed with the oscillator to produce the 3.5-MHz i-f. Signals from 11 to 18 MHz are mixed with the oscillator to also produce an i-f of 3.5 MHz. At any one oscillator frequency, the two incoming signals are 7 MHz apart. ..
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