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345 results found, displaying items 1 - 20
Garage Door Opener Parts Form IR Intrusion Detector
While creating an infrared beam intrusion detector system, the need for a beam-focusing method became evident. Parts from a modified Genie garage door Safe-T-Beam system, purchased at the local home improvement store, proved to be perfectly suited to the application. The main reason for choosing the Genie unit is that the IR transmitter and receiver housings each contain a plastic lens inside a short plastic tube molded into the housing. The tube and lens...
Simple Circuit Provides Latching Fault Protection
Most switching power-supply controllers provide non-latching fault protection. Satisfying a requirement for a latchoff response to a fault often requires the addition of excessive and redundant circuitry. For power-supply controllers with an external soft-start pin, however, a simple circuit can be added to convert its non-latching fault protection into one with latched protection. For typical controllers, the startup sequence begins by charging the VDD...
Improved Electronic Birthday Candles Provide Better "Blow Out" Simulation
An earlier Idea for Design described LED “candles” that you could blow out just like normal birthday candles (“Electronic Birthday Candles ‘Blow Out’ One At A Time”). A thermistor and heating resistor combination detected air blown over the thermistor. The control circuit incorporated an 8-bit shift register, a quad op amp, and driver transistors, allowing up to eight ...
Backstory: Full-Wave Active Rectifier Requires No Diodes
When Electronic Design asked me to write about my Idea for Design, first seen in this year’s August 13 issue, it seemed a simple enough task. We’re all familiar with design. Most of us do it in some form or another almost every day. But, ideas? We all have them, but where do they come from? And what is the essence of a good idea? Simplicity? Elegance? Performance, novelty, creativity? Thomas Edison once said that genius is 1% inspiration and 99% perspiration....
Use Hybrid PMOS-NMOS Active Loads To Cut Substrate Noise In Differential Amplifiers
BY MAKING A RELATIVELY simple change in a differential amplifier stage, designers can significantly reduce the sensitivity to digital switching noise. In mixed-signal ICs, digital switching noise couples through the common substrate into analog circuits, degrading their performance. In CMOS circuits, most substrate noise couples into NMOS transistors through backgate modulation. That is, the substrate acts as a second gate with a transconductance gain...
Interface Circuit Allows Users To Control DC Motor's Speed
THE CIRCUIT IN THE figure provides three levels of speed control for a dc motor, using a PC’s parallel port (LPT1). A C++ program performs the control functions by allowing the signals from the PC port to deliver three different voltages to the motor. The system is an interface circuit that connects the motor to the PC using a 4-bit binary counter (a 74LS193), three current- limiting...
Generate A Differential Signal Using A Transformer Plus Signal Splitter
Most function generators and network analyzers have one port to provide the output signal. If a differential signal is needed, then you may need to acquire a network analyzer with two output ports at great cost. Of course, there are alternate solutions in generating a differential signal without acquiring expensive equipment. The two most popular solutions include the use of a transformer or a power splitter. Why do we want to generate a differential ...
Create A Smart Cable To Ensure Quality Control And Authentication
A quick search of the Internet reveals that cloned or knockoff cables are a growing problem. Common complaints from cable users documenting this problem include intermittent signals, poor long-term reliability, and complete malfunctions. These complaints are the result of cheap wire, improper contact plating, incorrect wiring, and poor quality control. Electronic instruments alone provide no easy way to tell the difference between a genuine cable and an inferior...
Full-Wave Active Rectifier Requires No Diodes
A full-wave rectifier can be built without using any diodes. It exploits the fact that the output voltage of certain single- supply op amps is effectively “clamped” to ground (0 V) when the input signal goes negative. The circuit combines a unity-gain follower (IC1a) and a second stage (IC1b) that combines the follower’s output signal (VO) with an inverted version of the input signal (VIN) (Fig....
Sample 64 Temperature Points For Pennies Per Channel With Multiplexed Delta VBE Thermometry
Delta VBE ( VBE)-based thermometry is based on the “PTAT VBE effect,” which says that for an ideal transistor, the VBE corresponding to changes in collector current is exactly proportional to absolute temperature. Cheap small-signal transistors conform closely enough to the ideal model that VBE circuits can implement accurate and cost-effective thermometers needing no calibration. An earlier Idea for Design...
Simple Quadrature Decoder Suits Rotary Encoders
Rotary quadrature encoders often are used to command digital potentiometers or digital controllers, and quadrature decoding is typically performed in a programmable device (like an FPGA or microcontroller). This design performs quadrature decoding with commonly available components, and it comes in handy when you need to use a quadrature encoder in the lab or in a simple product. This design uses a manually turned contact encoder. Contact encoders are...
Programmable Window Comparator Uses A Single Reference
A voltage monitor is a common hardware need. But beyond a simple compare, many systems must provide a tolerance around a specific value. Specifications of 2%, 5%, or 10% typically require a windowed comparator, with a voltage reference and resistive divider components for setting the tolerance. All are available in many forms. The controller described here, based on the Microchip 12F675, allows the user to dynamically select the window characteristic as a ...
Triple-Current-Modulation Delta VBE Thermometry Cancels Ohmic Error Sources
Delta VBE-based ( VBE) thermometry1,2,3,4 is based on this classic bipolar junction I/V/T relationship: For an ideal transistor, the VBE corresponding to ratiometric change in collector current (I2 / I1) is exactly proportional to absolute temperature: VBE = 198.4 µV * °K * LOG10(I2 / I1). Because cheap, common, and robust small-signal transistors conform closely to the ideal model, circuits that exploit the “PTAT (Proportional...
Charge-Pump VCO Increases Parts Count But Saves On Cost
This charge-pump voltagecontrolled oscillator (VCO) has a number of neat features: single positive power-supply operation, positive VCO reference voltage, fast response, high linearity, temperature compensation, and open collector output. Seldom are all of these features present simultaneously. Though the component count is relatively high compared to commercially available devices, cost is low because all components are garden variety. Central...
Current-Mode Multiplier/Divider Design Eschews Passive Components
This circuit design for a current-mode analog multiplier/ divider is based on current-controlled conveyors (CCCII) and a second-generation current conveyor (CCII). No passive components are used. Analog multipliers and dividers are important building blocks in signal processing and are widely used in modulation systems. Also, for the same two inputs, the multiplier changes to a squaring circuit, which provides the energy content of the signal. ...
Monitor Transformer Winding's Temperature Without A Sensor
The use of a copper winding as a temperature sensor is not new. The traditional technique is to disconnect the ac power and the load and to quickly make the measurement using an ohmmeter. But the circuit presented here goes further. It can make the measurement in-circuit and in real time. The resistance value is derived by injecting a small dc current into the monitored winding and measuring the resulting dc potential. However, care must be taken to avoid...
New Math Technique Increases Temperature Accuracy Over 20,000%
Thermistors are extremely nonlinear devices. Because of the limitations of the mathematical model used, the devices’ ultimate accuracy is hardly ever fully realized due to the extra computational burden required to calculate the temperature from an accurate resistance reading. Fortunately, a minor modification to any thermistor equation will provide a worthwhile improvement in overall accuracy. This article shows how an improved mathematical model...
Sensor Signal Converter Outputs Both NPN And PNP Signals
Matching a sensor interface with a programmable logic converter or controller hardware that can accept only one type of input—npn or pnp—can be difficult. The last-stage modification circuit described here solves this problem. Designers can use it to convert an npn input to a pnp type or incorporate it in the last stage of the sensor design to generate both npn and pnp outputs. The npn and pnp transistors used in the circuit should be highcurrent- gain (hfe >...
Switching Circuit Increases Number Of USARTs Available From MCU
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...
Simple Solution Provides PWM Signal Fault Protection
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...
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