125 results found, displaying items 21 - 40

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...

A relative humidity meter can be built using a sensor with a capacitive response and a PIC microcontroller (MCU), as shown in the figure. The capacitance range of the sensor, the HS1101 from Humirel (www.humirel.com), varies from 162 to 202 pF. Functioning as an oscillator, a TLC555 CMOS timer performs the conversion from capacitance to frequency. The timer's frequency equation is given by: F = 1.44/(RA +...

If you need or want to have multiple operating systems on a PC, you should be able to access them separately. Some operating systems will take over all of the hard drives, and you may lose data or have data corrupted. (This is the voice of experience speaking!) So I came up with a simple fix that involves an external multiposition switch. This is easier than disconnecting the signal ribbon cable and the corresponding power connectors. Having two distinct operating systems...

Most digital timers require a set of dip switches or rotary BCD encoders to preset their interval. But those techniques consume eight or more inputs from a microcontroller's (MCU's) I/O lines. To alleviate the problem, this circuit forms a digital timer that only requires one input pin of the PIC16F872 MCU to adjust its interval (see the figure). The MCU performs all of the functions, a-d converting, timing, and decoding to drive...

In large projects, a single contractual document often known as the Contract End Item (CEI) governs the final product design. Each requirement of the contract is individually numbered to allow for performance verification of the end item. Because the projects are usually complex, this set of requirements is broken down and allocated to different subsystems. These subsystems also have a set of requirements, and each requirement must be traceable to a requirement above...

Certain irreversible operations (like releasing a parachute, cutting a rope, or starting a solid combustible missile engine) may be performed by pyrotechnic igniters. These devices generally consist of an electrically controlled igniter, some...

Usually, an MCU is considered a digital device. By default, its output voltage level can be either high or low and nothing in between. With the requirement to create an LED brightness control, the first idea that comes to mind is using a standard...

Here's a C/C++ program that converts decimal numbers ranging from 0 to 99,999 to binary and BCD formats. Using a simple algorithm in conjunction with pointer arithmetic and bitwise shifting increases the conversion speed without introducing...

Quadrature encoders have many uses in position-sensing applications. This implementation uses a Xilinx complex programmable logic device (CPLD) to count the pulses from the encoder and determine the direction indicated by those pulses (...

A pedometer is a device that counts the number of steps taken by a person and calculates the distance traveled by multiplying the number of steps by the length of the step. Here's a design solution for building a pedometer using the AVR MCU. The...

A very simple temperature indicator can be built around an 8-bit RISC microcontroller (see the figure). Data from a temperature sensor is processed by the MCU and used to display the temperature. The...

Nanosecond interval timers are a critical component in products as diverse as time-domain reflectometers (TDRs), collision-avoidance systems, radar altimeters, and nuclear instrumentation. This simple circuit, which runs off a single 5-V supply,...

Many science and engineering applications require an accurate frequency spectrum or Fourier transform of a signal. The Fourier transform of a sequence of samples of a signal is shown in Equation...

Building on the recent Design Brief theme of one-pin keypads, this design uses only one analog microcontroller (MCU) input to scan numerous keys, plus one resistor per key and another resistor and capacitor. The circuit is simply a crude...

Small or embedded systems often require a delicate measurement in the presence of high noise or interference. Without fancy filtering hardware, high-speed processing, or digital signal processing, it can be difficult to extract a stable signal of...

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