Analog Hotspot

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, ...

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...

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...

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,...

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...

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...

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...

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...

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...

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...

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 (...

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...

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,...

When I needed to create a simple tool to generate a long, event-triggered pulse, I started with a classic one-shot and a really large capacitor. This worked "pretty good," owing to the classic nature of the problem. There seemed to be no enthusiasm for using a small controller to provide the one-shot function, though. Nonetheless, there may be several advantages to doing so. Generally, larger caps have a wide initial tolerance and variation over temperature,...

The thermocouple is a popular sensor for industrial temperature measurement because it's accurate, cost-effective, widely available, and suitable for a wide range of temperatures. It consists of two wires of different metal or metal alloys, welded together at the sensing end (usually called the hot junction). The thermocouple output is a voltage difference across the other ends of the wires (called the cold junction), which must be maintained at a known temperature. If required...

This Design Brief introduces a computationally efficient network that computes the derivative of a discrete time-domain (digital) sequence. While recursive differentiating networks exist, this article describes a simple tapped-delay line (finite impulse response or FIR) differentiator that has guaranteed linear phase. Although the idea of differentiation is well-defined in the world of continuous signals, that's not the case for discrete signals. Fortunately,...

Many communities are installing gunshot detectors on lamp poles to help triangulate the location of gunfire during holidays or to help in responding to "shots fired" 911 calls. Besides location, another piece of useful information is the caliber of the gun that was shot. Fortunately, studies have shown that each caliber has a distinct noise spectrum. Police can use this spectrum to identify the gun's caliber, rather than using loudness, which isn't reliable. The circuit...

Switch-mode power supplies (SMPSs) traditionally are implemented using a basic analog control loop. But recent advances in digital signal controllers (DSCs) enable designs that begin to make fully digital control schemes practical and economical. Still, early adoption of this technology is expected to be in high-end applications, where the benefits of full digital control are the most immediate. Yet many analog power...

For applications requiring only a few milliamps of supply current, an RS-232 transceiver IC (MAX202) and a few external components can generate bipolar supply rails up to ±30 V. Such capability is useful ±15-V op-amp circuits that supply (for example) meter drive, LCD bias, and gasdetector bias. In the application for which it was designed, the internal charge pump of this IC generates ±10 V to drive an RS-232 line. ...

Seven-segment displays are needed in many instrument designs. In conventional microcontroller-based designs, four output port lines are allocated for one seven-segment display. Figure 1 shows the conventional design for four seven-segment LED displays. In this case, two eight-bit output ports are needed for four seven-segment displays. Figure 2 shows another popular...