Designing Ideas

You can employ a pin-limited microcontroller to develop a suitable dc/dc-boost-voltage converter with the aid of a few discrete components. Tiny microcontroller hosts dual dc/dc-boost converters details a simple circuit where a microcontroller powered by an AAA cell generates a high enough voltage to backlight an LCD.

Small capacitor supports telecom power supply during brownouts shows how to keep telecom equipment operational during a short brownout. The circuit charges a relatively small capacitor to twice the supply voltage to achieve brownout ride-through.

Overlap—the short period during which a push-pull drive's two transistors are both simultaneously on&mdas...Read More

The Design Idea in Circuit and software provide accurate recalibration for baseline PIC microcontroller's internal oscillator uses three I/O lines to recover the internal calibration value by recalibrating against a reference clock, the 4-MHz crystal.

The method in Microcontroller moving-dot display interface uses three I/O lines needs three output lines—data, clock, and latch—and requires some firmware and hardware. The moving-dot display has some benefits over the bargraph display: It better indicates a location of detected object in sonar and radar applications; it needs only one LED's current-limiting resistor instead of several; and it provides the same current ...Read More

Peltier devices, also known as solid-state refrigerators, or TECs (thermoelectric coolers), actively cool temperature-sensitive electronic components, such as optical detectors and solid-state lasers. However, one TEC data sheet proviso that designers sometimes miss is that you always measure these parameters with the TEC mounted on an effectively zero-thermal-impedance—that is, perfect—heat sink. Use thermoelectric coolers with real-world heat sinks presents derating curves for TECs.

Interface MIDI instruments to a PC through a USB port uses the FT-232BM from Future Technology Devices International, a USB-to-UART interface IC t...Read More

Chop the noise gain to measure an op amp's real-time offset voltage introduces a new type of chopping. "Chopping the noise gain" is a simple way to measure the offset voltage in real time, so that you can subtract it and enhance DC precision.

The circuit in Simple analog circuit provides voltage clipping and dc shifting for flash ADC converts a symmetrical inputvoltage range of 20.2 to 10.2V into the recommended 0.6 to 2.6V range of an ADC. The circuit also prevents the output voltage from going below –0.3V, which would probably damage the ADC.

Compact lase...Read More

To discover potential power-supply problems, you must run dynamic and static tests. The simple current sink in Precision voltage-controlled current sink tests power supplies tests low- to medium-power supplies and voltage sources. The current sink can draw current of 0 to 1.5A for an input-voltage range of 0 to 5V with a supply voltage as high as 20V.

Ordinary red LEDs normally function as light emitters, but they can also function as photosensors. In Red LEDs function as light sensors a single LED can even function as both a light emitter and a light detector in the same circuit . The basic idea is to pulse the LED, using the on-time to light it and the off-time to sense the ph...Read More

In general, audio equalizers need second-order bandpass filters. If implements using state variable techniques you would need three op amps per channel. The basis for an alternative, Audio equalizer features transimpedance Q-enhancement topology, uses SAB (single-amplifier-biquadratic) filters requiring only two op amps per channel.

AMI (alternate-mark inversion) is a three-level—positive, zero, negative—copper-cable transmission code with the useful property of having no dc component for ease of ac coupling using capacitors or line-coupling transformers and a spectral peak at one-half the symbol rate. The Design Idea, AMI-to-NRZI-direct-conversion circuit tolerate...Read More

In 1971, Signetics—later Philips—introduced the NE555 timer, and manufacturers are still producing more than 1 billion of them a year. As "NE555 timer sparks low-cost voltage-to-frequency converter" shows, by adding a few components to the NE555, you can build a simple voltage-to-frequency converter for less than 50 cents.

The circuit in "Optoisolators compute watts and volt-amperes" is an elaboration on that older circuit. It uses optoisolaters in a bridge circuit to measures not only watts, but also volt-amperes and so makes possible an estimation of power factor—watts divided by volt-amperes.

One way to obviate the nonlinear characteristic of an RTD sensor is to design analog hardware to perform the curve-fitting mathematics before any additional signal processing occurs. The approach in "Design an RTD interface with a spreadsheet" is especially attractive if you can keep both cost and component count low and if a microprocessor-driven design is not feasible.

Digital voltmeter (DVM) modules are very handy but also involve a significant number of design challenges. For example, their inputs are not isolated from the power supply, so you must add an isolated power supply. The opto-isolated flyback power supply in "Isolated supply powers DVM module"...Read More

A Hopfield network can convert analog signals into digital format and can perform associative recalling, signal estimation, and combinatorial optimization similar to the way a human retina performs first-level signal processing. "Flexible Hopfield neural-network ADCs quash noise" explores the Hopfield-neural-network paradigm for ADCs.

Listing 1, available with "8-bit microcontroller implements digital lowpass filter," shows a simple engineering method to design singlepole, lowpass-digital-filter firmware for 8-bit microcontrollers. The low-end Freescale MC69HC908QT2 is the target of the assembler program, but you can a...Read More

This Design Idea employs the Microchip PIC10F222 single-chip microcontroller. You program this microcontroller's internal memory using the MCLR pin. As the title, "Use the MCLR pin as an output with PIC microcontrollers," suggests, this Design Idea allows you to use the MCLR pin as an output pin during normal operation with the addition of a simple circuit.

You can use the circuit in "High-speed clamp functions as pulse-forming circuit"—a fast-response voltage limiter, or clamper—as a pulse-forming circuit. The input-voltage range is narrower than that of Schmitt-trigger circuits, because, at low input...Read More

Engineers have for many years used passive-CMV (common-mode voltage) inductive cancellation. Sometimes called a "humbucker transformer" because the power mains' 60-Hz "hum" is often a dominant CMV component. In the Design Idea "Actively driven ferrite core inductively cancels common-mode voltage," an active humbucker toroidal transformer is scaled up to handle any number of inputs and outputs.

The Design Idea in "Improved optocoupler circuits reduce current draw, resist LED aging" overcomes the problems of excessive power consumption, uncertain switching, and LED aging. It lends itself well to wide ac-range applications.

The CD401...Read More

In "Chopper-stabilized transimpedance amplifier nulls out background illumination," the reference signal from the light chopper as a square wave modulates the gain of an op-amp-based inverting amplifier. The modulated light beam at the same chopper frequency irradiates the photocurrent signal, which generates a voltage proportional to the amplifier's input, nulling out background illumination.

Microchip's PIC10F microcontroller family comes in a six-pin SOT-23 package that you can interface with an HD44780-compatible LCD display through a one-wire serial link using an asynchronous, simplified RS-232 protocol at 9600 baud, as detailed in "...Read More

With alternative power sources, such as wind or solar, a distorted 60-Hz sine wave is more likely to be present. To measure this distortion, you can use the THD analyzer in "Measure power-line distortion with a mixed-signal-THD analyzer" to monitor the fundamental frequency amplitude and the second-, third-, fourth-, and fifth-harmonic content of the input 60-Hz signal.

Thanks to the low-power requirements of today's electronic devices, you can power them wirelessly. "Wireless 'battery' energizes low-power devices" describes a simple approach to wirelessly transmitting energy to low-power devices at distances as great a...Read More

Some microcontrollers permit operation below a supply voltage of 3V, directly from a 3V alkaline or lithium battery. It is important to monitor the battery voltage to ensure system integrity, The monitor circuit in Battery monitor also enables constant-power-boost converter integrates an ADC within the microcontroller. The circuit in this Design Idea maintains constant power to a white-LED-display backlight by adjusting the duty cycle of a boost-power converter.

When you need to simultaneously sample a signal and amplify the signal level by a gain of two, you can cascade a common gain-of-one sample-and-hold amplifier and an amplifier with a voltage gain of two. Commonly, such an configuration has two external resistors that dissipate power even at the steady state of the sam...Read More

The circuit in Use a TL431 shunt regulator to limit high ac input voltage limits, or clamps, input-ac voltages higher than 260V rms to levels safe for the operation of the power MOSFET in an SMPS. Most isolated, offline SMPSs, including flyback, forward, and resonant, must operate at input voltages of 90 to 260V rms. Some cases even use line-to-line voltages of 400V rms, leading to increased component- voltage ratings and, thus, increased cost of the overall design.

In Autozeroed amplifier with halved noise needs few components you can exploit the fact that in an Analog Devices' AD8553 the two gain-setting resistors are separate and that the input stage is a voltage-controlled...Read More