Embedded Hotspot

From its introduction in 1995, the Universal Serial Bus (USB) quickly gained widespread acceptance for connecting peripherals to personal computers. More recently, its ease of use, expandability, high bandwidth, and low cost have suited it quite well for data transfer in embedded consumer electronic and mobile devices. Thus, product developers are increasingly being asked to design and implement a wide range of USB I/O devices. This idea describes a technique for...

I use this display circuit to expose students to the concepts and characteristics of scanning displays. Basically, a message is delivered to the CPU (a Microchip PIC16F76) over an RS-232 interface. The message is displayed on a vertical array of eight LEDs, which are spun by a dc motor. As they spin and take on new positions, the LEDs are updated with new lines of bit patterns, producing the display. In this way, the software allows the eight LEDs to emulate an 8-by-80...

At one time, reference designs were simply helpful guides to the finer details of designing a part into a board. Those days are long gone. The complexity of today’s devices, in addition to the fast pace of many markets, has forced some reference designs to evolve beyond educational tools into manufacturing documentation for fully defined end products (Fig. 1). This dual role leaves...

DIGITALLY CONTROLLED POTENTIOMETERS (DCPS) find uses in a wide variety of systems for setting bias currents, variable reference voltages, and calibration settings. In industrial control and automation applications, high accuracy is a must. DCPs with 1024 taps are available, but for a few dollars instead of tens of cents. A dual, 32-tap, 50-k DCP is available for 40 cents. Can we use both of the DCPs in the package and reach similar performance to the 1024...

HERE’S A C/C++ PROGRAM that converts decimal numbers ranging from 0 to 99,999 to binary and binary coded decimal (BCD) formats. Using a simple algorithm in conjunction with pointer arithmetic and bitwise shifting increases the conversion speed without introducing excessive memory overhead and programming complexity. When decimal numbers are within the range of 0 to 9, their binary and BCD representations are identical, requiring only four bits...

SOME BACKGROUND Also known as state diagrams, statecharts can be found on napkins and coding screens as designers turn ideas into application code. They’re simple to use and understand, as they’re just a bunch of “circles and arrows and a paragraph on the back of each one explainin’ what each one was, to be used as evidence against us,” to quote Arlo Guthrie and his classic song, “Alice’s Restaurant.” Events cause transitions...

Measurement and process control loops often use 8-bit microcontrollers. The devices are inexpensive and widely available, and they can be programmed in many popular high-level languages—like C and Basic. However, if the loop requires a nonlinear sensor, the designer faces the added challenge of having to develop a software linearization algorithm. One solution is to design hardware to perform the required curve fitting before the sensor’s output...

The Universal Asynchronous Receive and Transmit (UART) interface is found on a variety of peripheral devices. Consider, for instance, a microcontrollerbased system with four such peripherals. Ideally, in low-cost embedded applications, you would like to connect multiple peripherals to a single UART. However, a lack of chip-select signals in UARTs complicates such a task. This is a common design problem, and there are a few conventional ways of...

The best way to make midrange, low- to medium-accuracy temperature measurements (considering size, cost, performance, and ease of use) is to use an IC temperature sensor. But most IC temperature sensors are designed for applications where the circuits to which they connect are nearby. Therefore, the inclusion of sensing, digitizing, and signal- processing functions in one IC greatly simplifies the design of such sensors and the data-acquisition interface. ...

Voltage-to-current converters that feed grounded loads are common in industrial measurement and control applications. The conventional "textbook" circuit uses both positive and negative supply rails. An earlier article by this author titled "Voltage-To-Current Converter Works From A Single Supply Rail" (Electronic Design, Feb. 17, 2003, ED Online 2985) described a circuit that could power grounded loads and needed only a positive ...

Many small microcontrollers require so little power that often they can draw what they need through their loads. This can simplify a system, reduce its cost, increase its reliability, and provide unexpected benefits. One example is an automotive check system that monitors a car's brake lights and indicates any faults through an incandescent bulb in the instrument cluster, LMP1 (Fig. 1)....

LEDs are often used on manmachine interfaces (MMIs) or device front panels to illuminate switches or backlight text information so that the user knows what the device is supposed to be doing at the time. Occasionally, the designer wants these LEDs to start blinking at a particular rate to alert the user to a condition needing attention, such as a low battery. Many devices use embedded microprocessors or microcontrollers to handle the MMI, along...

Traditionally, interfacing a microcontroller with an n-by-m keypad required n + m of the microcontroller's I/O pins for keypad scanning. Keypad designs that conserve microcontroller pins have been developed, but they require additional resources, such as external ICs or a built-in analog-to-digital converter (ADC). The design presented here uses only one I/O pin and requires only resistors and a capacitor as external components. I/O is a bidirectional pin initially...

Eight-pin microcontrollers offer numerous peripheral features. However, the maximum number of I/O pins available is often limited to six, since two pins would be required for the chip's power supply. So, it can be challenging to design systems based on these devices, especially if they involve a significant display requirement. For instance, controlling a large number of LEDs is a problem with eight-pin microcontrollers, unless you resort to a method called...

The growing need for security and enhanced functionality in the banking, identification, and telecom markets has increased the use of smart cards worldwide, to the detriment of the low-security magnetic-stripe cards. However, the development of the hardware and firmware needed for proper communications in a system based on a smart card poses new challenges to designers. Unfortunately, only some high-end microcontrollers have a dedicated UART (universal...

Many microcontrollers feature a pulse-width-modulated (PWM) output that can be low-pass filtered to produce a variable dc voltage. Without additional circuitry, however, this technique is limited to controlling very low-power loads. The circuit here illustrates a scheme that lets this dc voltage control a high-power load, such as a motor, actuator, or heating element (see the figure). Furthermore, the load voltage may be higher...

Many electronics applications require various processes to be monitored and controlled, generally under microcontroller supervision. The proper timing to, say, turn a motor on or off, or to open or close a valve, is critical for an efficient control system. Here's a simple and low-cost method to obtain five independent voltageadjustable clock signals that offer a timing resolution of better than 0.1%. This accuracy holds over a very wide range of time—from 0.5...

WILLIAM GRILL, Honeywell Aerospace-Olathe, Olathe, Kansas william.grill@honeywell.com Over the years, many sensor monitor designs would have benefited by being able to have their encoded pulse-width modulation (PWM) data forwarded to and post-processed by a PC-based host. However you encode the PWM information, the PWM-to-RS-232 translator described here has a small footprint and a total cost under a few...

The simple method described here evaluates a one-wire device that uses pulse-width-encoded communications from a PC serial port. Communications errors such as parity and acknowledge are monitored. The hardware interface to the PC is a MAX232 driver/receiver, and the slave in this example case is a Texas Instruments TMP141 temperature sensor. The circuit can be expanded to four sensors on the same bus by using the TMP141's four programmable addresses derived from A0 and...

Working on an embedded project? An 8-bit microcontroller with a pulse (PWM) peripheral can provide a low-cost and easy solution to adding natural voice to your next embedded endeavor. We recently implemented this technique in SuitSat-1 (see "Latest Radio Amateur Satellite Is No Empty Suit," March 16, 2006, p. 25). Listeners could hear recordings of schoolchildren saying "greetings from space," as well as telemetry readings (time, temperature, and battery voltage). ...