Embedded Hotspot

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). ...

A recent project required an inexpensive microprocessor that could be battery operated and indicate if the batteries were low. I chose Microchip's PIC16LF84A for the microprocessor because it was simple to program and could operate between 2.0 and 5.5 V dc. However, the PIC16LF84A doesn't have analog or comparator inputs. To meet the design criteria for a battery monitor, I went with Microchip's inexpensive MCP100315 Microcontroller Supervisory Circuit. It costs $0.33 each in...

The semiconductor industry’s rapid move toward a 90-nm process node to achieve performance and cost benefits puts enormous pressure on power budgets. Decreasing transistor sizes lead to increased leakage current and, as a result, static power. Dynamic power also rises with system speeds and higher design density, but in a more linear fashion. Today, many designs have 50-50 static and dynamic power dissipation. According to International Technology Roadmap for Semiconductors (ITRS)...

In many instances of microcontroller firmware design, it's necessary, or desirable, to take four individual bytes and access them as if they were a single 32-bit variable, maybe as a pair of 16-bit variables, or even some other combination. One way to merge the four bytes into a single 32-bit variable would require reading the least-significant byte into the 32-bit location, then shift-left by "8," then OR in the next byte, then shift-left by "8,"...etc.—until the 32-bit...

This simple serial RS-232-to-discrete-output application and driver, based on Texas Instruments' 74LV8153, requires only a minimum of parts. The single-wire, RS-232 bit-compatible 74LV8153 supports an internal clock, auto-baud function, and output registers. Graphic control written in Visual Basic (VB) gives this implementation a Windows-based feel. The circuit is intended as a resource for bench-switch or power-supply controls. Referring to the schematic in ...

The circuit that's shown in Figure 1 implements a programmable 0- to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing VL = VW. At the digital pot's zero scale, where VWB ≈ 0 V, the voltage across RSET will approach zero and...

The circuit shown in Figure 1 implements a programmable 0- to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing V_L = V_W...