345 results found, displaying items 21 - 40

This design builds on a previously published Idea for Design (“Talk To Multiple Devices With One UART”). Our solution allows you to increase the number of USARTs (universal synchronous, asynchronous receiver/transmitters) available on a microcontroller with minimum hardware. Typical 8- and 16-bit microcontrollers have one programmable USART for communication. But designers...

This idea was created to solve a design problem we faced a few months ago. The circuit we were working on was used to steer an H-bridge that was controlled by a TMS320F2810 digital signal processor (DSP). During the final phase of the design, we discovered by chance that everything worked fine when the circuit was initially powered. However, if it was powered off for 5 to 15 seconds and then powered on again, the circuit started draining a lot of current...

Many industrial and control applications use analog current loops as the physical link for measurements and actuator control. Although several ranges are used, the most popular is still the 4- to 20-mA standard. Loop accuracy depends on the transmitter’s ability to transform the sensor signal to a current. It also depends on the stability of the current-transfer function (measured at the receiver) with respect to temperature, physical length of...

One application I recently dealt with needed multiple phases of sine waves, all of equal amplitude. I considered 45°, 60°, and 90° differences, but decided 60° was the best solution. I scoured the Internet for a circuit. Unfortunately, while multiple phases exist, and the topologies are legion, no topology offered sine waves of equal amplitude with a 60° phase shift. I thought the solution would look like a common three-op-amp phase-shift oscillator, so that was...

Not properly closing a refrigerator door will no doubt invite huge electricity bills. This gadget is an alert device that beeps if you leave the refrigerator door open for more than 20 seconds. When the door opens, the lamp illuminates and the IC (a 4060B counter/oscillator) starts counting down. After a preset delay of 20 seconds, the piezoelectric buzzer beeps intermittently for 20 seconds and then stops for the same amount of time. This cycle...

In an application using a pin-limited microcontroller (MCU), I needed to scan an array of 16 buttons. The technique I used involved a series string of resistors of identical value connected between two bidirectional pins of the MCU. For simplicity, the example shown uses five resistors to scan four buttons (see the figure). A metal pad is created at each juncture between the resistors. When a person...

The accurate transmission of analog signals over long distances in noisy industrial environments is a difficult design problem. One of the oldest solutionsisolated current loopsis still one of the best. This Idea For Design presents a simple optically isolated linear current loop receiver that uses generic parts. The receiver operates from a single non-isolated power rail (12 V) to generate a convenient analog 5-V voltage-mode output that’s ready for further...

Bias circuits for class AB buffers (Fig. 1a) can take several forms. One alternative (not necessarily the best) is usually called the “old VBE doubler” (Fig. 1b). The main purpose of these circuits is to provide VCC-independent (and very often thermally compensated) bias for output transistors, so every effort is made in this direction. But...

Even robotic systems occasionally need a cooling fan. When they do, the cooling circuit must be an intelligent one that makes minimal demands on power consumption and space. The circuit described here is such a cooling fan driver for an active heatsink assembly. The driver uses readily available and inexpensive components, and it runs on a 12-V dc supply (see the figure). The circuit uses an LM35...

Noise measurements can be problematic. They often yield a different result with every measurement, even when nothing in the circuit is changing. The test circuit in the figure minimizes this uncertainty in equipment performance (but not, of course, in the device under test). The circuit does this by providing reference points in the noise-versus-frequency output generated by the network analyzer. The usual setup for noise testing consists of the...

Designers can use specialized ICs as a simple way to add touch-sensing capabilities to a circuit. For instance, the Cypress CapSense devices can handle several touch buttons and a touch slider. In some designs, however, one button might suffice. One example is a “touch-to-talk” intercom application. In this case, a mixed-signal programmable system-on-a-chip (PSoC) will do. The PSoC has digital blocks that can be configured as a sensitive proximity detector and...

Today’s micro- and nano-structured sensors boast excellent linearity, resolution, and wide measurement ranges. As a result, microelectromechanical systems (MEMS) are playing an increasing role in many more applications. This design describes a novel use of such a sensor—a non-contact differential variable-reluctance transducer (NCDVRT)—in the pressure port of a system. The application involves the selection of a stainless-steel membrane and...

The data sheet for the LT3080 linear voltage regulator suggests using printed-circuit-board (PCB) traces for ballast resistors. Although the LT3080’s low offset voltage suits it well for this technique, it can be used for other ballast applications— for instance, for a set of bipolar transistors. For example, in the figure, ballast resistors R1 and R2 can be short lengths of copper trace. In a practical case,...

The prescaler described here connects to the front end of a 100-MHz frequency counter to extend its coverage range to 10 GHz. The circuit is a far less expensive way to measure frequencies above 100 MHz than buying a 1- or 10-GHz frequency counter. The divider was built inexpensively. Creating this low-cost prescaler required some tradeoffs, and some rules were not followed (discussed later in the article). When you use this or any similar ...

I needed a simple LED indicator showing that a particular voltage level had been reached—specifically, that a capacitor had charged to a particular potential. I was convinced that there must be a way that a programmable zener diode, such as the TL431, could be used but I found no simple circuits. My first thought was just to connect a series current limiting resistor and LED to the cathode so that the LED would light when the reference potential was reached...

After Electronic Design asked me to contribute something to this special issue, all kinds of possibilities ran through my mind. After all, it had been 40 years since my first ED article, which was itself an Idea for Design (IFD), “Gated Amplifier Uses FET in Feedback Loop,” in the Jan. 4, 1968 issue. So, what’s an IFD? The snappy answer is that it’s one of Electronic Design’s most popular editorial features. But more germane...

Linear Technology’s Chief Technology Officer Robert Dobkin has been contributing Ideas for Design (IFDs) since his youth. He’s still enthusiastic about them. “I remember one I wrote when I was a kid. It was a current source that you could pulse on or off. I don’t know how many letters I got from that,” he said. “It had just two or three transistors in it, but it was really effective in terms of people coming back to me after reading it, which...

Electronic Design published my first Idea for Design, “AC-DC Converter Runs Off One Power Supply” (April 16, 1992, p. 93), more than 16 years ago (Fig. 1). It set a theme that I have continued to employ ever since—using the nifty venue of IFDs to present and develop new circuit design ideas and themes to the engineering community. Over the years, examples of some of those basic concepts and ...

After Electronic Design asked me to contribute something to this special issue, all kinds of possibilities ran through my mind. After all, it had been 40 years since my first ED article, which was itself an Idea for Design (IFD), “Gated Amplifier Uses FET in Feedback Loop,” in the Jan. 4, 1968 issue. So, what’s an IFD? The snappy answer is that it’s one of Electronic Design’s most popular editorial features. But more germane is...

FIGURE 1 DEMONSTRATES A one-way switchedcapacitor gain stage circuit, performing a voltage gain of AO = C1/C2 only during the decreasing trail of the input signal VI (with VJ = 0). During the positive signal variations, the output doesn’t change, thereby implementing an incremental peak-detector and accumulator circuit. This device can be used to measure the...

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• Control circuit keeps dc motor running at constant speed