345 results found, displaying items 41 - 60

IN APPLICATIONS REQUIRING ABSOLUTE accuracy in the speed control of dc servo motors, there’s no substitute for the traditional tachometerbased feedback loop. But for somewhat less demanding situations, adequate accuracy often can be achieved without the complication and expense of a tach. This can be done by taking advantage of the built-in electromechanical constants of the motor itself. For example,...

SOME MULTI-STRING LED MODULES come with a common-anode configuration. The commonanode connection reduces the number of wires between the LED module and its driver from 2N to N+1, where N is the number of LED strings in the module. In this idea, we’ll drive a commonanode LED module while simultaneously limiting the LED string voltage when an LED string becomes open. Figure 1 shows the LT3496...

I WAS REMINDED RECENTLY of a tester I designed years ago. At the time, I wanted to build “The Ultimate Continuity Tester,” and I established a wish list of all the features I required: • A “real continuity” tester. Too many multimeters and sounders react at resistances as high as hundreds or even thousands of ohms, which makes them practically useless in many cases. Within a board or a system, there are always medium-conductivity...

IN CONSUMER ELECTRONICS APPLICATIONS, which tend to be lower in frequency and less demanding than typical clock-buffering applications, inexpensive high-speed op amps (~100-MHz bandwidth) can offer an attractive option in place of traditional clock buffers. High-speed amplifiers can be less expensive than traditional clock buffers, yet they’re able to accommodate a wide range of design configurations. For instance, one good alternative for...

THE SOARING COSTS OF fossil fuels, combined with environmental concerns like climate change, are driving the increased interest in renewable (“green”) energy. No energy source is “greener” than hydroelectric power, particularly small (“microhydro”) installations that involve minimal artificial water impoundment and associated environmental impact. Even with an adequate water source, however, efficient and cost-effective implementation of appropriate...

It’s fair to say there are really two kinds of reference designs. One is developed by chip companies that want a permanent foothold in an original device manufacturer’s high-volume platform in a consumer market. The other is produced by a chip company’s Web-based or downloadable PC tool that lets ordinary bench engineers mix and match ICs, simulate circuits, and obtain bills-of-materials (BOMs) and sometimes actual circuit board reference designs. ...

The filter described below is useful for detecting a signal that’s closely surrounded by spurs, even when the task is complicated by the frequency of the signal of interest wandering by a few percent. For example, in telecom, a pilot signal can originate from sources scattered around the world. Assume a 10.0-kHz signal of choice. Due to variations in oscillators, temperature conditions, and aging, a frequency deviation of ±200 Hz can be...

Galvanically (that is, optically or electromagnetically) isolated 4- to 20-mA current loops offer robust noise immunity and tolerate long cable runs. These advantages, combined with simple unshielded two-wire cabling, make this mature signaling standard popular for transmitting analog data in noisy industrial and process control environments. Unfortunately, the conversion of an analog voltage output to an isolated current-loop signal is relatively complicated. In...

This idea describes a white- LED (WLED) driver circuit controlled by a simple ambient light sensor (ALS). A typical application would be a brightness control for cell-phone backlighting. On a very sunny day, the brightness will increase to improve the visibility. The circuit uses the IA2505 four-channel WLED (Fig. 1). Each LED can be driven up to 20 mA, with the drive current...

A few simple components are all it takes to create an over-temperature alarm. The circuit in Figure 1 requires only an ordinary negative-temperature-coefficient (NTC) thermistor, two common ICs, and a handful of discrete components. The circuit uses a unipolar 12-V supply and consumes only a few milliamps in the idle state. This circuit is particularly suitable for monitoring the temperature of heatsink plates. ...

Privacy has become a major issue with the near ubiquitous availability of cell-phone cameras. Some people have called for a preliminary “privacy flash” that goes off just before the full flash in order to warn people that their picture is being taken. In fact, such a flash is required in Italy. You can implement a combination privacy- and full-flash light using simple logic gates along with an LED driver (see the...

New operational amplifiers optimized for high-performance audio and ultrasound applications combine extremely low total harmonic distortion plus noise (THD+N), -130 dB, with large output voltages on heavy, 600-? loads. One would think this might be the universal building block. In real life, it’s a bit more complex. For instance, op-amp input capacitance has a nonlinear behavior that’s a function of the input voltage. The associated input current will...

The proportional-control solenoids used in some industrial hydraulic systems are usually driven by microcontrollers or programmable logic controllers (PLCs). Such complex drivers typically require several different supply voltages for logic and control. (The purpose of proportional control is to move the solenoid plunger to an arbitrary position and leave it there.) A set-and-leave solenoid driver, however, should not require a costly PLC or the...

A circuit used to control the level of a video signal should have a 3-dB cutoff frequency of greater than 5 MHz for a television application or 100 MHz for a monitor application. CMOS-based digital potentiometers typically cannot be used as video devices because their frequency responses barely exceed 1 MHz. For such applications, a good choice would be a variable-gain amplifier (VGA) with analog or digital gain control. VGAs are offered...

In designing a simple spectroscopy setup, we needed to synchronize the speed of a small, inexpensive dc motor precisely to 6000 rpm (100 Hz). Our first idea was to take a phase-frequency detector type of phase-locked loop (PLL), the CMOS 4046, to maintain not only the speed, but also the phase to the reference signal. 1 In the classical approach, the motor’s speed is modeled as a firstorder time delay over time. Some math is done to obtain a good ...

The circuit shown in the figure can monitor resistance in a noisy or otherwise hostile environment. A 1:1 transformer provides isolation and a good common-mode rejection ratio (CMRR). The resistance across the secondary winding is reflected to the primary, where it forms a voltage divider with resistor R1 (see the figure). This divider produces a reducedamplitude clock signal that's coupled through C2, rectified by ...

The most common method for interfacing multiple switches—multiplexing— allows for the connection of (N/2)2 switches with N microcontroller IO lines. The method described below, which has its roots in an LED interface technique commonly known as “Charlieplexing,” makes it possible to interface N*(N – 1) switches with N IO lines. In conventional multiplexing of an N-by- N matrix with 2N IO lines, half of the lines are configured for input and...

This circuit creates a set of LED-based electronic birthday candles that are just as much fun as blowing out wax candles, but are also reusable, scalable, and even eco-friendly. It uses a thermal sensor that’s maintained at a temperature above the ambient temperature. When you blow air over the sensor, the resistance changes. The circuit detects this change and turns off the eight LEDs. When you stop blowing, all but one of the LEDs turn on. This cycle...

Adding “intelligence” to measurement systems has become commonplace because 8-bit microcontrollers are inexpensive and widely available, and they can be programmed in many of today’s popular higher-level languages (e.g., C and Basic). Often, the main challenge is signal- conditioning the sensor’s output into a signal-ended voltage that can fully exploit the input span of the microcontroller’s analog-to-digital converter (ADC). By using basic math and a...

• Whatever Happened To Heathkit?
• Precision DC motor speed controller
• Hot Hands For Some Cool Rock: Motion Sensing Meets Audio Engineering
• Voltage-To-Current Converter Works From A Single-Supply Rail
• Control circuit keeps dc motor running at constant speed