Ten best ways to split a voltage rail

Electronics Weekly

By richard wilson 2nd February 2015

There are a number of reasons why an engineer would want to “split” a voltage rail in their design. Sometimes parts of the circuit, like a sensor or an IC, require a bipolar supply. 

Other reasons are to make the best use of the dynamic range of your ADC if it has a bipolar input, or to generate a mid-rail bias voltage in a single supply rail system. Whatever the reason, this article collects together a variety of different techniques that can be used, including some more unusual ones.

Some of the techniques given have a small footprint with low number of external parts, or a low quiescent current.

There are several different meanings of the phrase “rail splitter.” The usual meaning is creating a new “0V” reference point, usually the mid-point Vdd/2 of a single supply rail Vdd.

Figure 1 – TLE2426 Classic Rail Splitter IC Equivalent Circuit

The available voltage remains the same as before, only you can view it as being distributed as a bipolar supply ±Vdd/2 about the new “0V” reference. A linear conversion is often used to generate Vdd/2, but a switched-mode conversion can also be used for high output power.

The new “0V” can be called a “virtual ground.” Figure 1 illustrates the concept, where an input voltage is divided by two and buffered to give Vout.

Another type of rail splitter takes a single rail Vin and splits it into bipolar outputs, ±Vout. For example, 3.3Vin might be “split” into ±5Vout. Such a process is usually done using two switched-mode conversions, often a boost plus a buck-boost regulator.

A third type produces a negative output from a positive input, for example creating –5Vout from 5Vin, to give a ±5Vout bipolar supply. (It could be argued that a different terminology should be used, as these circuits don’t create a new “0V,” so they aren’t virtual ground circuits.)

Using a UART to Implement a 1-Wire Bus Master

 TUTORIAL 214

Sep 10, 2002

Abstract: This application note explains how to use a microprocessor's UART to implement a 1-Wire® bus master. It includes an explanation of the required electrical interface, UART configuration, and timing relationship between UART and 1-Wire signals. The flexibility offered in setting up UART byte timing allows straightforward implementation of 1-Wire time slots as well as the reset and presence detect pulses. With the inclusion of deep transmit and receive FIFOs, several byte values can be transferred on the 1-Wire bus with just a few clock cycles per bit required from the main processor.

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5V to 3.3V Converters for Microprocessor Systems

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Hand Soldering for Through Hole Components

App note: High power LED driver with PIC12F675

Dangerous Prototypes  
September 15, 2012 in Uncategorized by DP

A current controlled buck converter for driving high-power LEDs. The PIC12F675 microcontroller has an integrated comparator, which in combination with a low pass filter provides a control circuit for the SMPS.

The circuit is based on a buck topology switching power supply using the on-chip comparator peripheral within the PIC12F675 microcontroller. The switching power supply design ensures efficient power transfer between the system battery and the output LED. Using the attached Flash microcontroller as a control for the driver circuit expands the capability of the circuit to include intensity control, automated intensity compensation for low battery conditions, and the ability to playback preprogrammed Flash sequences. The Flash microcontroller also allows the creation of a custom PC-based graphical user interface, using the PICkit Flash Starter Kit for programming the preprogrammed Flash sequences. The combination of the switching power supply design and the microcontroller results in an efficient circuit with advanced automated features while keeping the circuit simple and inexpensive.

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Tiny Synchronous Step-Up Converter Starts Up at 700mV

Linear Technology

Design Note 428 
Dave Salerno11/07/428

Figure 1. Single-Cell 1.8V Boost Converter for a Bluetooth Radio Application Features a Low Startup Voltage and Uses a Monolithic Chip Inductor for a Maximum Component Height of Just 1mm.

Introduction
Alkaline batteries are convenient because they’re easy to find and relatively inexpensive, making them the power source of choice for portable instruments and devices used for outdoor recreation. Their long shelf life also makes them an excellent choice for emergency equipment that may see infrequent use but must be ready to go on a moment’s notice. It is important that the DC/DC converters in portable devices operate over the widest possible battery voltage range to extend battery run time, and thus save the user from frequent battery replacement.

Single-cell alkaline batteries, with a 1.6V to 0.9V range, present a special challenge to DC/DC converters because of their low voltage and the fact that their internal resistance increases as the battery discharges. Thus, a DC/DC converter that can both start up and operate effi ciently at low input vvoltages is ideally suited for single-cell alkaline products

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Maven of Meth

The real-life chemist behind television’s preeminent crystal cook

Donna Nelson, associate professor of chemistry at the 
University of Oklahoma

September 5, 2012 • By Vince Beiser

Bad news, entrepreneurial fans of Breaking Bad, the hit AMC series about a middle-aged chemistry teacher turned drug kingpin: you cannot actually learn to cook crystal meth by watching the show. “They deliberately put in faulty steps. They’ll start with one method of synthesizing methamphetamine but then switch to another,” says Donna Nelson, professor of chemistry at the University of Oklahoma. “It’s like watching a video of someone starting out on a trip to Dallas and ending up in Chicago.” The abundant “meth” that appears on-screen is actually cotton-candy-flavored sugar crystals, she promises.

Nelson isn’t just a well-informed observer; she’s been consulting on the Emmy-winning drama since its second season, helping to ensure that the show’s writers make the chemistry of illegal drug-making credible.

Voluble and cheery, with an understated Southern drawl, Nelson may not have specific expertise in the subject—“I’ve never synthesized anything illegal,” she insists—but she does have appropriate credentials for the job. Originally from the small Oklahoma town of Eufaula, Nelson picked up an interest in science from her father and grandfather, both doctors. In 1983 she became the first tenure-track female professor ever hired by the university’s century-old chemistry department. She estimates that she has taught organic chemistry to nearly 10,000 students. She has also racked up awards and honors from institutions ranging from the National Science Foundation and the Ford Foundation to the National Organization for Women.

Bryan Cranston, left, and Aaron Paul of Breaking Bad

Nelson got involved with Breaking Bad after reading an interview with its creator, Vince Gilligan, in Chemical & Engineering News. “He said neither he nor his writer had a science background, and so they had to rely on Wikipedia and the Web,” she says. “When I read that, I thought, ‘We scientists are always complaining about shows getting the science wrong. It’s like fingernails on a blackboard to us. This would be a great opportunity to work with one.’”

Her second thought, however, was “Wow, do I want to get involved with this show? I wouldn’t want to do anything that looks like it condones illegal synthesis. People say it glamorizes illicit meth labs.” After watching a few episodes, she stopped worrying. “It portrays the characters getting beat up, shot at, having these horrible lives,” she sums up. “I don’t think any kid watching it would want to be like that.” She asked Chemical & Engineering News to let Gilligan know she was willing to offer her services, and quickly heard back from him. By then the show was getting pointers on meth-making from a DEA agent, but Gilligan was especially interested in Nelson’s experience as a chemistry teacher. On a trip to San Diego soon after, Nelson took a detour to Burbank to meet with Gilligan, and has been involved with the show ever since.

In one of the first scenes Nelson was asked to help with, the show’s antihero, Walter White (played by Bryan Cranston), was supposed to explain the nomenclature of alkyne hydrocarbons to his high school chemistry class. “When I saw what they had written, I thought, ‘Wow, they really need help,’” she recalls. She rewrote much of the dialogue and handed the staff some explanatory diagrams, which she was delighted to see Cranston re-create precisely on-screen on the classroom blackboard.

The chemistry of meth cooking is no secret; there are recipes all over the Internet. One of Nelson’s tasks is to help choose particular cooking methods and calculate how much of each ingredient is required. In one episode, Cranston and his young sidekick, played by Aaron Paul, can’t find any pseudoephedrine—a common meth precursor chemical often extracted from cold medicines. The two steal some 30-gallon drums of methylamine to use instead. “I looked up the exact process in which you’d use methylamine and did all the calculations on how much it would yield,” says Nelson. Turns out there are several different processes one can use. “They chose the one that was easiest for the actors to say.”

The show is now in its fifth season, and Nelson is clearly enjoying the secondhand glamour it brings her—she even made a brief cameo appearance as a nurse in one episode, she says, but wound up on the cutting-room floor. Meanwhile, she’s hoping to leverage her Hollywood cred by making a public service announcement warning Oklahomans about the dangers of crank. That idea came from a recent meeting with the state’s governor. “She told me,” says Nelson, “that the biggest problem we have right now in the state is illegal meth synthesis.”

Simple electronic fuse.

john

August - 4 - 2009; Comments

Description.

This is perhaps one of the simplest electronic fuse circuit one can make. The circuit uses only one transistor, one SCR, one push button switch and two resistors.

 The working of the circuit is very simple. Initially the load current flows through SCR and resistor R1.The value of R1 is so selected that, the maximum load current multiplied by the resistance of R1 is equal to 0.7 volts. When the load current exceeds the maximum value the voltage drop across R1 becomes more than 0.7V and switches transistor Q1 ON. Now the transistor completely bye passes the load current and the current through triac falls below the holding current. This makes the triac OFF. When SCR is OFF there will not be any current flow through R1 and so the voltage across it falls to 0.This makes the transistor OFF, completely isolating the load circuit.The fuse can be resetted by pressing S1.When S1 is pressed the SCR is again triggered and remains latched to conduct the load current.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• The value of R1 can be obtained from the equation; [Imax] X [R1] = 0.7V.
• R2 can be obtained from the equation; R2 = [Vs] X [1K Ohms].
• Wattage rating of R1 can be obtained from the equation; W = [Imax] X [Imax] X [R1].
• For this circuit to work the current consumption of the load must be greater than the holding current of the SCR.

What's All This P-I-D Stuff, Anyhow?

Electronic Design

Bob Pease

June 26, 1995

Recently, I wrote about refrigerators,1 pointing out that there are several ways to control a servo loop, such as a temperature chamber, or an oven, or a refrigerator using thermoelectric coolers (let's leave bang-bang controllers and on-off heat-movers out of this). Fuzzy Logic controllers can work pretty well, and so can a P-I-D (or PID) controller. That's pronounced "pee-eye-dee", not "pid". Several readers said that they were not very knowledgeable about PID controllers. They don't teach very much about them in schools these days, I guess. They asked me, "Please show us a good example of a PID controller." Well, I agree completely that an example is one of the most powerful tools. I'll show you a couple of examples, so you can see how easy it is to come up with one yourself. And I will point out that, after a Fuzzy Logic expert showed us his best example of a nice simple F.L. controller, I had no idea how to make it myself. Do you know how to run a F.L. controller after seeing an example of one? I don't. I hope that would not be true for my examples.

One example is found in my book on Troubleshooting,2 where I had to control the temperature of a blast of heated air. When you apply more watts to the heater, there's a delay before the sensor warms up to its new temperature. In fact, there are and . This is a fairly interesting kind of system for closing the loop accurately, but not really difficult. Engineers have known how to do this for many years—about 140 years, I would say. Back in the 1880s, when most servo loops were mechanical or pneumatic, and the instrumentation was crude, it was a wise person who understood how to close a loop with good accuracy and loop stability. But for the last 40 years, when a good operational amplifier costs $22 or even less, it's been a piece of cake.

Note, a wise old colleague observed that the introduction of the Integral term to Control Theory is credited to the 1930s. But I found good documentation in my Encyclopedia Brittanica3 that a flyball governor with an integral term was invented by Sir W. Siemens in 1853.4 Never bet that the British didn't get there first. However, I can't say that I've seen the Derivative effect exploited in that 1894 Encyclopedia. So maybe the PID controller is only about 60 years old...

First of all, let's discuss the nomenclature—"PID." That stands for , and , and . You can build some controllers using only P and I, and others using only P and D, but when you need good performance, using all three terms can provide REAL advantages. Let's see how these terms are made, and how they are used.

LM555 Makes Inexpensive Power Driver

Electronic Design

Rick Mally
August 31, 2012

Various digital circuits require push-pull power drivers, particularly for gate and line driver applications. Many special-purpose devices are available for these issues, but they are typically expensive and single-sourced, with a short product lifecycle that forces a costly redesign when they are discontinued. Fortunately, the ubiquitous LM555 timer (non-CMOS versions) can serve as a very inexpensive and capable driver.

With its powerful totem-pole output and a 4.5- to 16-V supply range, the LM555 can be used as either a buffer or an inverter. If more than one driver is required, designers can use the dual LM556 to reduce cost and footprint. The rare 558, a quad version, can also be applied as a quad inverting driver.

To implement a buffer function, configure the timer’s reset line (pin 4) as the input (Fig. 1). This provides a transition level of 0.5 to 1 V, allowing the device to be driven directly by standard 5-, 3.3-, and even 1.8-V logic regardless of the VCC level. Alternatively, the trigger line (pin 2) may serve as an active-low enable line, although this line does not have the same compatibility as the reset pin in terms of levels.

1. By using the LM555’s reset pin as the input, the timer can serve as a buffer circuit driven by standard logic levels from 1.8 to 5 V.

In the inverting configuration, the trigger line is used as the input, with a transition threshold of 0.334 × VCC (Fig. 2). Additionally, the reset line could be used as an active-high enable line with the same transition levels, including the 1.8-V logic level, as stated above.

2. Designers can also employ the LM555 as an inverting driver by configuring the trigger line as the input.

With its 200-mA sink/source capability, an LM555 powered by 12 or 15 V can drive most MOSFET/IGBT gates at frequencies exceeding 250 kHz without clamping diodes on the gate, minimizing cost. When driving gates, you should place a 5- or 10-Ω resistor in series with the output to minimize ringing and transient currents. In addition, the circuit should include a ceramic or tantalum bypass capacitor or at least 1 µF to provide the surge currents required.

Both of the circuits also provide an additional open-collector output on the discharge pin (pin 7) that could be set to any voltage level, up to 18 V. You can let the control voltage pin (pin 5) float, or you could use it to change the internal comparator threshold levels.

mTouch Metal Over Cap Technology

Microchip AN1325

As a user interface, capacitive touch has several advantages: it is low power, low cost, simple to implement, reliable mechanically, and it allows designers a great deal of freedom in the shape of the buttons. However, for all its advantages, the field effect nature of capacitive touch still has some limitations.

1. Standard capacitive touch systems normally do not work through metal coverings.
2. It requires special software to operate in environments with radiated and/or conducted noise.
3. Reading buttons in the presence of water or other contaminants can be difficult.
4. It is problematic for visually impaired users that rely on Braille.
5. It has trouble detecting a touch through gloves.

Microchip’s new Metal Over Capacitive user interface system overcomes all of these limitations without compromising power consumption or design simplicity. This application note describes how to create an
interface using the Metal Over Capacitive touch system.

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1951 Mechanix Illustrated Uncovered

Beers in Bunnie's Workshop - Workshop Video #36

Using the PIC Devices' SSP and MSSP Modules for Slave I2C Communication

AN734

Date:  9/2/08
Author:  Stephen Bowling, Naveen Raj

Description:
Many devices in the PICmicro family have a Synchronous Serial Port (SSP) or Master Synchronous Serial Port (MSSP). These peripherals can be used to implement the SPI TM or I 2 C communication protocols. The purpose of this application note is to provide the reader with a better understanding of the I 2 C protocol and to show how PICmicro devices with the SSP or MSSP modules are used as a Slave device on an I 2 C bus.

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Raising the dead: Can a regular person repair a damaged hard drive?

By Joel Hruska on July 27, 2012 at 9:54 am

On June 22, 2012, my primary hard drive, a Samsung HD103SI, quietly passed away. There was no warning — no grinding, no clicks, clacks, or sudden bang. One moment, I was working on a story, the next, I wasn’t.

It quickly became clear that something more serious than a simple system lock had happened. Post-reboot, the HDD would spin up smoothly, beep 12 times, and then spin down. The drive was never recognized in BIOS, which nixed any chance of using disk recovery software to extract data.

This is a story of my efforts to repair the drive myself, my research into the question of whether or not users can repair modern hard drives, and the results of my efforts. If your drive is still detected in BIOS, you may be able to use software tools to retrieve your data. Here, we’re going to focus exclusively on hardware-related failures, and what your options are.

Part of the reason for writing this story is that data recovery is difficult to accurately research unless you’re fairly versed in it to start with. There are dozens of data recovery firms, all promising clean rooms, the latest tools, and highly trained professional staff. Many firms refuse to publish their prices online, which makes comparisons difficult, and it’s apparently common for small companies to farm tough jobs out to larger ones.

This one, for example, is pretty much toast

Step 1: Broadly identify the type of problem

There are two broad categories of problems that can nuke a drive: PCB issues and internal component failures. If the problem is inside the drive, skip down to Step 3. If the problem is on the PCB, there is a glimmer of hope.

The world’s first 3D-printed gun

By Sebastian Anthony on July 26, 2012 at 10:56 am

An American gunsmith has become the first person to construct and shoot a pistol partly made out of plastic, 3D-printed parts. The creator, user HaveBlue from the AR-15 forum, has reportedly fired 200 rounds with his part-plastic pistol without any sign of wear and tear.

HaveBlue’s custom creation is a .22-caliber pistol, formed from a 3D-printed AR-15 (M16) lower receiver, and a normal, commercial upper. In other words, the main body of the gun is plastic, while the chamber — where the bullets are actually struck — is solid metal.

The lower receiver was created using a fairly old school Stratasys 3D printer, using a normal plastic resin. HaveBlue estimates that it cost around $30 of resin to create the lower receiver, but “Makerbots and the other low cost printers exploding onto the market would bring the cost down to perhaps $10.” Commercial, off-the-shelf assault rifle lower receivers are a lot more expensive. If you want to print your own AR-15 lower receiver, HaveBlue has uploaded the schematic to Thingiverse.

HaveBlue tried to use the same lower receiver to make a full-blown .223 AR-15/M16 rifle, but it didn’t work. Funnily enough, he thinks the off-the-shelf parts are causing issues, rather than the 3D-printed part.

While this pistol obviously wasn’t created from scratch using a 3D printer, the interesting thing is that the lower receiver — in a legal sense at least — is what actually constitutes a firearm. Without a lower receiver, the gun would not work; thus, the receiver is the actual legally-controlled part.

In short, this means that people without gun licenses — or people who have had their licenses revoked — could print their own lower receiver and build a complete, off-the-books gun. What a chilling thought.

But hey, that’s the ambivalent nature of technology, the great enabler. In just the last few months, 3D printers have also been used to print organs, blood vessels, and drugs. In a few more years, when 3D printers move beyond plastic resins, who knows what we’ll be able to print.

Jim Williams on Bridge Circuits

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Some random hints for quick hand SMD assembly

Using SMD Components on Breadboards

instructables

To use SMD components on breadboards, simply use 0.1" spaced male headers, cut a piece of two pins, and solder the SMD component in between the two pins on the shorter end of the header.

This works well with 0603 and 0805 sized components, as shown in the pictures.

SMD components are much cheaper, and they also fit on perfboards. I never buy through hole components any more.

The Chemistry of Fireworks