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294 results found, displaying items 1 - 20
Driver Offers Proportional Solenoid Control Without PLC, Microcontroller
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...
Create A 250-MHz Bandwidth Digital Potentiometer For Video Level Control
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...
Use PWM To Maintain Motor Speed And Phase While Eliminating Loop Filter
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 ...
Circuit Transfers Resistance Value Through Isolation Barrier
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 ...
Novel Switch Interface Scheme Reduces Microprocessor Pin Count
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...
Electronic Birthday Candles “Blow Out” One At A Time
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...
Interfacing Linear Sensors To An ADC Requires Only Basic Math
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...
Analog Switch Connects One I2C Bus Master To Multiple SFP Modules
Telecom and data-communications equipment commonly use small-formfactor pluggable (SFP) modules for the physical-layer interface. Also common in these systems is an I2C bus for the management data input/output (MDIO) interface. But when several SFP modules are used, they all have the same I2C address. As a result, they can't all connect to the same I2C bus. To avoid the need for multiple I2C bus masters in that situation, ...
Create RS-485 Adapter To Convert Data Lines From Full- To Half-Duplex
Multiprotocol interface ICs can be used to connect a UART to an RS-485 bus architecture called point-to-point full-duplex (PTP-FD). The PTP connection usually requires drivers and receivers to be constantly enabled, and therefore "present" on the line. So when such a circuit board must fit into a point-to-multipoint, half-duplex system (PTM-HD), the entire board (usually) must be redesigned. A simple trick, though, can adapt an existing PTP-FD board, which provides a single...
High-Speed Full-Wave Rectifier Requires No Diodes, Few Parts
Systems requiring power conversion and level detection employ full-wave rectification, traditionally provided by a diode bridge. But diode bridges consume a significant amount of board space and reduce signal amplitude. An alternative solution involves using separate amplification for the positive and negative half-cycles and a comparator to switch between them. This solution typically requires numerous ICs and can suffer from delay mismatch between the two...
Use Current-Mirror Biasing To Avoid Squegging In RF Oscillators
If you've ever designed an RF oscillator, you've probably encountered squegging. Sometimes called "motor boating," squegging causes oscillators to start and stop at frequencies much lower than the frequency of interest. Viewed on an oscilloscope, squegging looks like bursts of oscillations. On a spectrum analyzer, it looks like a Christmas tree. In some designs, such as super-regenerative receivers or wildlife radio tags, this might be a desirable side effect. In most cases,...
Simple Circuit Indicates Whether A Signal Is Logic High Or Low
The circuit presented here (see figure) provides users with an indication of a high or low logic state. When the input is a logic 1 (high), the common-cathode display indicates "H." When the input is a logic 0 (low), the display indicates "L." The circuit uses one gate out of four...
Add Position Detection Capability To Light-Curtain Circuitry
Light curtains use a linear array of LEDs and optical detectors to sense when an object breaks a light beam. Then they trigger an alarm output. However, light curtains typically don't provide spatial data to indicate where along the light curtain the light beam was broken. The design shown here adds that feature. It describes a circuit that senses where along the light curtain the beam was broken and transmits the location to a PC via RS-232. The length and resolution of...
Anti-Theft Alarm Lookalike Protects Parked Motorcycles
Sometimes, a simulated anti-theft device can deter a would-be thief just as well as an actual alarm system. To that end, the circuit in the figure automatically flashes two super-bright LEDs, mounted in the rear-light cluster of a motorcycle, to simulate the warning commonly used to...
Create A PWM Signal Simply, Inexpensively
Sometimes you need to generate a pulse-width-modulation (PWM) signal for your circuit to simulate a certain behavior. The technique described here generates a simple programmable PWM signal for less than a dollar. The technique uses an MSP430F20xx 14-pin microcontroller (MCU). The devices in this series incorporate Timer_A2, which allows you to generate one PWM signal without CPU intervention. The timer houses two capture-compare registers, called CCR0 and CCR1, which...
Adding Feedback Boosts Peak Detector's Precision
The standard way to measure the peak of a signal involves the use of a diode. But if the diode is used alone, the input voltage must be significantly larger than the diode's turn-on voltage to obtain acceptable accuracy. Because turn-on voltages range from 200 mV in germanium diodes to 700 mV in silicon diodes, a simple diode peak detector requires an input voltage of 2 to 7 V, respectively, to achieve a 10% error. You can significantly improve resolution and accuracy in...
Create A High Input Impedance, Rail-To-Rail Measurement System
Two very desirable features for a precision measurement system based on an analog-to-digital converter (ADC) are high input impedance and a wide input range, ideally including or extending slightly beyond the power-supply rails. The circuit described here does just that. Its very high input impedance is complemented by an input range that extends 300 mV beyond the supply rails. The example circuit uses a thermocouple and a resistance temperature detector (RTD) connected to...
Simplified AC Line Sensor Uses Few Parts, Little Real Estate
Typically, ac line sensors use comparators. But I had to design a power supply to be as low in cost as possible, be self-powered, use through-hole components, and take up as little space as possible on a small two-sided pc board. So I developed the simplest ac sensor possible. The resulting circuit senses the high-voltage dc bus (...
Key Design Aspects Of CMOS Image Sensors Revealed
What’s going on inside the latest cameras has a lot to say about the state of the art in digital imagers. This report offers tear-down analyses of CMOS image sensors (CISs) in mobile phones and professional digital single lens reflex cameras manufactured by Canon, Micron, Omnivision, Sony, and Toshiba. It’s particularly interesting to examine the cell-phone end of the spectrum. CMOS image sensors have become the image capture technology of choice for the...
Drive Large 7-Segment LED Displays Using Only 1 Or 2 MCU Pins
Many options exist to drive seven-segment LED displays, but most are limited to low output currents. The approach described here uses one 74ALS374 or 74AS374 octal latch, wired as a shift register, per digit. The 74ALS374/74LS374 can handle an output sink current of 24 mA per bit, and the 74AS374 can handle 48 mA per bit, suiting it for large bright displays. Using this approach, you can not only generate the numbers 0 through 9, but also leading zero suppression,...
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