Monthly Archives: June 2016

Why Do ICs Need Bypass Capacitors?

Any electronic design engineer will vouch for the necessity of supplementing integrated circuits on their PCB with bypass capacitors, although they may not understand the reason to do so very well. As a rule of thumb, engineers provide every IC with a 0.1µF ceramic capacitor next to its power pins in each circuit board they design. Along with proper PCB layout techniques, adding a bypass capacitor improves circuit performance and maximizes the efficacy of the ICs.

The trouble lies with transition currents. Circuits handling digital signals produce rapid transitions when their signals switch states. When digital circuits output a high state, the signal voltage is very close to the supply voltage. When they output a low state, the signal voltage reaches very near the ground voltage. When transiting from a low to high or a high to low, the voltage swing from supply to ground or from ground to supply, causes a transient current to be drawn from the supply.

Usually, power to an electronic circuit on a PCB is fed at a single point and traces on the PCB carry this power to each IC. Traces on the PCB have their own parasitic inductance, which, when coupled with the source impedance of the power supply, react to transient currents by creating voltage transients.

The trouble aggravates when ICs have to drive low-resistance or high-capacitance loads. The low-resistance demands high currents when the digital state changes from low to high. Again, when the digital state changes from high to low, there is a demand for the load current to reduce suddenly. However, according to Lenz’s Law, an induced current will flow such as to oppose the change that produced it.

The net effect of transient currents and the parasitic inductance of PCB traces and wires are to create high-magnitude voltage transients, ringing or severe oscillations in the power lines. This can lead to suboptimal circuit performance or even to system failure. Engineers at Texas Instruments have demonstrated an improperly bypassed line driver IC switching at 33MHz can induce ringing amplitude of the order of 2V peak-to-peak on a 5V power rail.

Placing a 0.1µF ceramic capacitor close to the IC power pins improves the situation, because capacitors store charge. Placing the bypass capacitor close to the IC allows low resistance and series inductance. The bypass capacitor is therefore in a better situation to supply or absorb the transients on the PCB traces, which have a comparatively larger resistance and series inductance.

Although engineers refer to such components as both bypass and decoupling capacitors, there is a subtle distinction between the two terms. Decoupling refers to the amount by which one part of the circuit influences another. Bypassing provides a low-impedance path allowing noise to pass by an IC on its way to ground. A capacitor, placed close to the IC supply pins, accomplishes both decoupling and bypassing. However, a decoupling capacitor has an additional task. It blocks the DC component of a signal and prevents it from traveling through to the next part of the circuit, while allowing the AC component little or no resistance at all.

Raspberry Pi Rover to Mine Water on Mars

Water is an essential chemical for sustaining any sort of life on the planet Earth. From what knowledge space explorations have provided us so far, this is true for life elsewhere in the universe as well, but there are deviations. Mars being our closest neighboring planet, it is only natural for us to try to locate water there. Additionally, with the human population on our home planet close to its saturation point, it is essential we plan to distribute the excess populace on nearby planets. For this, we need to make sure of the presence of water there or at least, the possibility of generating it simply and easily.

Collaboration between the Gilmour Space Technologies, Australia and the Singapore University of Technology and Design is exploring the Mars Aqua Retrieval System or MARS. This is a prototype for harvesting water from the soil of the Red Planet. The team has built the prospecting rover for less than $10,000. Based on the famous Single Board Computer, the Raspberry Pi and an Arduino unit, the rover uses microwaves to heat up and release the frozen water present in the Martian soil.

Although designed to work on Earth, the proof of the concept takes its basic idea from the discoveries made so far by Curiosity and the Phoenix Mars Lander. These extraordinary rovers have indicated the presence of water on the Red Planet. This water either is in non-liquid forms such as ice or buried in its soil. Engineers have designed the rover MARS to extract water from the Martial soil, collect and store it. With NASA recently declaring the presence of running water on Mars, project MARS has taken on an even greater importance.

Detailed documentation of the project indicates scientists considered various methods for each step of the process. The final concept involved separating and collecting water using microwaves and a cold trap. According to tests conducted by the team, they claim to have collected four grams of water from frozen soil in four minutes.

The process of water collection involves cycles of locating the MARS system using its two powered wheels to move to the target area, lowering a microwave unit over the ground and then heating the area for about 20 minutes. This releases steam from the Red soil and it enters a collection pipe leading to a condenser bag, where the steam condenses into water that finally drips into a collection box. The entire process is similar to distillation in any chemistry laboratory.

Although NASA provided only a meager budget of $10,000, the team has managed to create a prototype that presently functions satisfactorily on Earth. The two SBCs the Arduino and the Raspberry Pi in MARS control the locomotion and timing, the arm movements and the on/off switching of the microwave. The prototype is able to withstand 30% of the pressure and temperature conditions present on Mars.

According to Adam Gilmour, CEO of Gilmour Space, the US space agency has reacted favorably to the details of the MARS design sent to NASA. Although, in its present form, the prototype is unlikely to leave Earth’s atmosphere, MARS will be available for public view at the Gilmour Space Museum, north of Australia’s Gold Coast.

Keep Your Fish Happy with a Raspberry Pi

People who keep fish in aquariums at home know it is important to feed them timely and to keep their habitat clean. Trouble starts when the owner has to leave home for a few days and cannot find a knowledgeable caretaker to take care of the pets. Cabe Atwell tried to solve the problem he faced in an ingenious way – by using the power of the Internet.

Cabe had an automatic fish feeder, but he also enlisted the services of a friend to keep an eye on her goldfish, the friend was not sure of what was required and the automatic fish feeder broke down. Fortunately, the losses were not fatal, but Goldie the goldfish grew to double her size because of overfeeding. This led Cabe to work on a system to allow watching and feeding the pet over the Internet.

Cabe wanted a system that would allow seeing the fish in real time, anytime, by moving a camera around the tank. The next requirement was sensing the tank water temperature and cutting off the power to the tank bubbler and air filters, if necessary. It was also necessary to feed the fish manually, and above all, to do this through a network and ultimately, via the Internet.

Cabe’s research led to the conclusion that a Single Board Computer such as the Raspberry Pi or RBPi and a Pi camera would be most suitable for seeing the fish via the internet. For the other features, an Arduino Uno was more appropriate.

Accordingly, Cabe selected two small Nema 17 mount stepper motors, available on Adafruit, for the driver components. The motor controls came from an Arduino Motor Shield, which made it simpler to drive the motors. Cabe designated one motor for allowing movements in two directions, while the other rotated the food container to dump fish food into the water.

The fish feeder was a modification of the original malfunctioning feeder. It consisted of a drum to hold the fish food. When rotated completely around, a simple trap door opens briefly to let a small amount of feed.

To keep the camera motor traveling too far, Cabe incorporated limit switches in both directions. The limit switches were placed in position using rare-earth magnets, which allowed easy adjustments for the movement range. A surplus belt driven motion platform provided an affordable arrangement for viewing the entire length of the tank.

For sensing the water temperature, a waterproof digital temperature sensor was the most suitable – DS18B20. Although fresh-water fishes are more tolerant of water temperature variations, loss of air-conditioning or heating arrangement can lead to the tank water becoming too hot or cold for the comfort of its occupants.

For the video stream, Cabe settled on VLC since it was easier to use. VLC offered the maximum resolution of 640×480 pixels at 15 frames per second, which Cabe found adequate for keeping a tab on the fish. A simple AC relay took care of feeding power to the air filters and bubbler.

For the future, Cabe wants a better AC control and more sensors for measuring the pH, ammonia and nitrate levels in the water.

How Does Switching Affect Semiconductors?

Even though ICs rule the world of electronics, the transistor does all the work. Within each IC are millions upon millions of transistors perpetually switching on and off so that the IC can carry out its intended functions. Even if one of the multitudes of transistors were to stop switching, the IC could lose part or all of its functionality.

Circuits handling digital signals most often use transistors to switch from a high state to a low state and vice versa. It is usual to call a circuit point as being in a high state if the voltage at that point is close to the supply voltage. If the circuit point is closer to the ground or zero voltage, we generally call it as being at a low state. The time taken for the transistor to switch from a high to a low state or vice versa is its switching rate. While the transistor does not expend much energy when at either the low or the high state, the same cannot be said for the time when it is actually switching.

Under ideal conditions, a transistor should switch instantaneously. That means the transistor should take zero seconds to change its state. However, ideal conditions do not happen in reality and the transistor takes a finite time, however small, to actually switch over.

Transistors are made of semiconductor material and each junction has a finite capacitance and resistance. Junction capacitances store energy and the combination of resistance and capacitance acts to slow down switching – the capacitance must fill up or empty itself before the transistor can flip. The rate at which the capacitance fills up or empties itself depends on the junction resistance.

The situation gets worse as the switching frequency goes up. As the transistor is driven to toggle faster and faster, the junction capacitance may not get enough time to discharge or charge up fully. That defines the maximum switching rate the transistor can achieve.

Semiconductor manufacturers use various methods to reduce junction capacitances and resistances to induce these special semiconductors switch faster. Although modern semiconductors (transistors and diodes) are capable of switching at MHz or GHz scales, the cumulative effect of the tiny switching losses add up to increase the junction temperature.

Power is the product of voltage and current. When a semiconductor is in a high state, although the voltage is high, the current is negligible and consequently, the power drawn from the supply is negligible. When the semiconductor is a low state, its voltage is close to the ground level and the product of current and voltage is again negligible.

However, during switching, when the voltage is somewhere in-between the supply and ground levels, the current drawn also increases. That makes the product of voltage and current have a significant value and the semiconductor generates heat because of the power consumption. With higher frequencies, this happens more frequently and the heat accumulates to produce higher junction temperature.

If the natural process of heat dissipation can remove the accumulated heat, the semiconductor soon reaches a steady temperature. Else, heatsinks and or forced cooling methods are necessary to remove the heat accumulated.

A New 6 Axis Motion Sensor

Except for professional photographers using tripods, most people now use the camera within their smartphones to capture images of their surroundings. More often, unless your hands are exceptionally steady, the captured image is somewhat blurred. The act of holding the smartphone, aiming it properly to frame the image and touching the capture icon induces tremors and shakes that prevent the camera from capturing a steady picture.

To counter the lack of stabilization when capturing images on a hand-held gadget, manufacturers are incorporating mobiles with motion-sensors. These detect the tiniest of hand movements and cancel out the effects by making suitable corrections to the camera. Most motion-sensor devices are MEMS or Micro-Electro-Mechanical Systems based solid-state devices.

A global semiconductor leader, STMicroelectronics is a manufacturer and supplier of MEMS devices for consumer and mobile applications. ST is now offering the most advanced six-axis motion-sensing MEMS device that fully supports image stabilization for smartphones, tablets and Digital Still Cameras.

The iNEMOTH is the new range of inertial motion sensors from ST and includes the 6-axis motion-sensing IC, the LSM5D53H, which combines a 3-axis gyroscope and a 3-axis accelerometer. LSM5D53H is a System-in-Package solution offering its users the smallest package size with an ultra-low-power processing circuit that makes it the industry’s lowest power consuming IC.

LSM5D53H uses two techniques for minimizing image blurring that usually happens because of camera motion while capturing a snapshot. The first technique is the EIS or Electronic Image Stabilization, while the other is the OIS or Optical Image Stabilization. Although these techniques were initially meant for use on professional cameras, they are increasingly being deployed in tablets and smartphones. They are helpful in reducing image blurring that is likely to occur when the user is taking a snapshot with an outstretched arm.

ST has the necessary expertise and designs high-end gyroscopes for OIS. The company also plays a pioneering role in providing dual-core gyroscopes. These are capable of handling user motion and gesture recognition simultaneously while providing camera image stabilization. The LSM5D53H builds on this expertise.

Within the LSM5D53H is a tiny, ultra-low-power MEMS module. The IC allows equipment manufacturers to minimize the size, cost, system complexity and extending battery life for mobile devices with imaging applications. While systems employing two single-function gyroscopes consume 5mA, LSM5D53H does the same work while consuming less than 1mA and 1.1mA in its high-performance mode.

Offering an optimal motion experience and always-on low-power features for the consumer, the LSM5D53H system-in-package offers a 3D digital accelerometer and a 3D digital gyroscope performing up to 1.6 KHz ODR. Manufacturers can connect the device to the camera module via a dedicated auxiliary SP interface, while the primary interface is available via I2C or SPI.

ST manufactures the various sensing elements using their specialized micro-machining processes. They develop the IC interfaces using CMOS technology as this allows them to design a dedicated circuitry. The ST manufacturing process then trims the circuitry to match the characteristics of the sensing element in the best possible manner. The acceleration range of the LSM5D53H is +/- 16 g, while it has an angular rate ranging +/- 2000 dps.