Category Archives: Electronics

More and more design operations become automated. These changes give many benefits like effectiveness, minimal errors and less routine operations to designers. Modern electronic equipment require very precise planning as devices shrink to minimal sizes, operation power increases and also have to fit to it external design requirement. So designing is a very complex task where without smart CAD software would be almost impossible to do.

When designing a new electronic device you have to deal with several areas that is necessary to make device reliable and attractive device. All of these areas usually are done on particular CAD system. Most common CAD based electronic specific task are:

• Mixed Analog-digital device modeling;

• Programmable Logic modelling and synthesis;

• HF circuits and electromagnetic modeling;

• Functional modeling;

• PCB Design;

• Thermal modeling;

• Chip topology modeling.

Each of these modeling and designing processes require different skills and knowledge.

Lets go through each to see their specifics and what CAD systems are used to automate related tasks.

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It is obvious that for most of drivers car is more than transportation vehicle. Sometimes people spend hours in the car everyday and listens not only news radio broadcast, but also listens music. To have good quality music sound in the car require more than good speakers and power amps, but also some smart solutions are needed to make it sound better.

In the current time there are plenty publications on how DIY good car sound system at home. But again even best power amplifier do not guarantee that car music will sound as Hi-Fi class. Main problem is bard installation of audio-system inside the vehicle. In many cases speakers are installed where ever they fit in the car. But there is also no clear answer where it is the best place to install speakers and how. The most common mistake is to place powerful high quality speakers in the rear shelf while in front position por speaker are installed or not at all. Such audio system installation gives a feeling line he is sitting back to scene.

First of all it is important to keep in mind that purpose should be not to install more powerful audio system with poor characteristics, but to install audio system with wide dynamic characteristics for listeners who sits in front seats of the car. So first solution of this is to install dynamics in proper front place.

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Among usual antennas used in todays data transfer there are also different type of antenas used. First publications about electrodynamic characteristics of fractal structures were published in 1980′s , but first practical approach appeared after 10 years. Dr. Nathan Cohen professor of boston university designed, engineered and patented many practical fractal antenna solutions and founded “Fractal Antenna Systems” in 1995.

As Nathan states in centre of Boston there were forbidden to use external antennas in city so he managed to hide antenna within design of amateur radiostation. He took aluminum foil and made antenna as decoration according to Van Koch figure:

This figure builds as follows: first line (length is z)is cut in 3 even pieces z/3. In the middle the triangle is formed with same side lengths z/3 and same angles. This way wee get single element template. Then repeat this process with other segments where sizes diminishes 3 times (z/9) then follows again 3 times (z/27) and so on. This way fractal size doesn’t change.

Today fractal antena technology is in early stages, because engineers are doing empirical experiments to find out what geometrical structures give better results. During these experiments they found out that using ordinar type antenna templates building fractals give better gain coefficient. Like this antenna type:

This type of structure is so called recursive tree. Each new iteration multiply branches by two and lowers resonance frequency. So using iterations it is possible to use antenna at lower frequencies without increasing antenna size.

Dipole antennas usually have narrow band-about 2.4% around frequency carrier. If 5^th iteration is used then this parameter grows up to 3.1%. If 3D tree is used (when there are 4 branches used instead of 2) then this parameter grows up to 12.7%.

Besides Dipole antennas there are resonant loop antenas used. Loop antenas are build using Koch figures:

Ordinary frame antenas have low input impedance what makes difficult to connect to feeder. Fractal loops allow to increase impedance even for frequencies lower resonance and this way effectiveness increases.

Another thing what makes fractal antennas so attractive is that they can be fabricated using PCB making methods. Because of compact size they can be put directly on PCB inside like cell phone.

Additionally to narrow band antennas there one type of antennas – wide band. These are Sierpinski antennas are frequency independent and have several bands of resonance and can be compared to log-periodics and spirals. Frequency independence is a result of retaining similar shape at many scales. Sierpinski fractals doesn’t require additional space while frequency band grows as it happens with spiral and log-periodic antennas:

Sierpinski fractal antennas can be successfully used in automotive where transparent antennas are sticked to the front window (or other) and can receive multiple bands independently to to standard and country.

Another widely used example is cell phones. They are long time using internal fractal antennas:

This allow to use multiple bands like 900MHz, 1800MHz, 1900MHz and so on.

Source: RA-2002-09

Originally by Anisimov Ivan

In many cases can be very handy to be able to convert 1.5V to 5V. Then you can power microcontroller or LED from a single AA or AAA battery. It is simple to do this as there are special IC’s as MAXIM MAX1674 or MAX7176. This is step-up DC-DC converter that can convert voltages from 0.7V to any in range from 2V to 5.5V. MAX1676 have already preset pins for 3.3V and 5V, that makes easer integration in 3.3 and 5V circuits. IC can dissipate up to 444mW.

Bellow is a circuit that converts 1.5V to 5V.

Lets say wee need to get maximum output current 300mA, then wee need to put some efforts. Because output power is 5V·0.3A=1.5W. Lets say efficiency is 100% then the power drawn from battery will be 1.5W too. At 1.5V voltage this will be 1A current. Not all batteries can drive such currents. Other important part is inductor. For this wee need inductor with high current saturation which usually leads to increase of size.

• If current is over 300mA, then inductor inductance 47uH;

• If current is over 120mA, then inductor inductance 22uH;

• If current is over 70mA, then inductor inductance 10uH;

You will find recommended inductors in datasheet.

In this case if FB pin of MAX1614 is connected to ground, then output voltage is equal to 5V. If FB would be connected to OUT pin then output voltage would be 3.3V. If put voltage between OUT and ground, then we can control output voltage in range from 3.3V to 5V.

Biggest real efficiency of IC is at 120mA – 94%.

Manufacturer recommends to design PCB with sort and thick traces. Inductor should have minimal resistance.

Real device shows really big efficiency at high loads. Circuit and PCB is really compact allowing to make small designs.

In picture bellow you can see how circuit works with LED Luxeon without current limiting resistor. Circuit is powered with 1.5V Kodak battery. This circuit can be used for powering LED flashlights, emergency cell phone charging, making compact embedded designs with microcontrollers, bugs.

Original source: www.radiokot.ru

Ultrasounds transducers for measuring distances are commonly used in robotics, automotive parking sonars. Ultrasound distance measuring is non -contact measuring method – radiation and reception of ultrasound waves. Ultrasound waves are mechanical acoustic waves with frequencies more than 20kHz. Normally human cannot hear frequencies above 20kHz while some animals can. For instance bats use ultrasound location of objects. Dolphins communicate with each other using ultrasound signals.

Ultrasound interacts with hard body and part of incoming wave energy is reflected back, in other words – it is back scattered. So direct wave towards object is back scattered widely – up to 180°. If object is moving – received frequency differs because of Doppler effect. Lets say simple example – parking sonar. Distance to object can be calculated very simply by formula:

L=v·t·cos(α)/2

Where t- time period between transmitted and received signals; v – ultrasound speed; α – signal angle to object. If signal is perpendicular to object then cos(α)=1.

Each Ultrasound transducer has its impedance characteristics. Usually operation frequency is at lowest impedance point where sensitivity is highest:

Typical transducer operates at 32kHz. If working mode is continuous then two transducers are needed: one for transmission and second for reception of wave signals. If impulse is used, then only one transducer is enough as Ultrasound transducer can operate as transmitter and receiver.

Ultrasound is generated pretty simply. It is because of special properties of material which is used to deformate because of voltage applied. When some frequency applied (usually resonance) then ultrasound plate starts mechanically oscillate and generate sound. In reception mode transducer plate generates voltage because of material deformation forced by mechanical waves:

Of course there is whole physics pf piezoelectrics which I won’t discuss here. And typical transducer used in Ultrasound distance measuring transducer often used in parking systems looks like in picture bellow:

 

The most common method is of constructing embedded controller systems is a Printed Circuit Board (PCB). I think all electronics know, that simple PCB is constructed of insulating material like epoxy impregnated glass cloth with a thin copper sheet(s) on one or both sides.

There are many conflicts about requirements on how to design interconnection patterns of PCB. But the main purpose for all is to make PCB reliable, effective and producible. If circuit operates in low speed, then requirements are not as strict as for high frequency devices where parasitic effect cannot be ignored. Each PCB stray has its own resistance, capacitance and inductance. These are main effect that distort the signals.

Ground and Power planes

This is not very actual for hobbyists as they usually develop single or double side boards. But if design uses four layer board, then it is recommended to dedicate two layers for power and ground. So two PCB plains in parallel form a parasitic power supply decoupling capacitance which reduces power supply noise. And of course these plains act as a shield for electromagnetic radiation.

Many circuit problems can be caused of improperly implemented ground. It may cause from noise or erroneous operations to safety problems. Fro instance, because of excessive inductance there can “ground loops” appear. Or maybe because of bad insulation between different grounds like earth, analog, digital the circuit wouldn’t work. Even wrong grounding path may induce a voltage for another circuit. The solutions to these problems may vary. Sometimes it is enough to reduce current flow by using single point ground and shielding.

EMC

Electromagnetic Compatibility (EMC) problem arrise when there are a big number of electronic devices used witch radiate electromagnetic energy at frequencies close to communication frequencies. To solve EMC problem first you need to identify it, then you need to eliminate or reduce it to defined limits by using shielding or simply removing/replacing noise signal source.

ESD

Electrostatic Discharge (ESD) is also important consideration in embedded systems. ESD also have potential for failures and errors in operation. ESD usually occur if there is an external electric fields near by. Then the impressed voltages may reach tens of thousands Volts. This simply can happen if you just walk in humidity environment before touching the device and damaging it. The cure is only one- using grounding and shielding.

Currently there are huge amounts of different digital IC chips available in the market starting from simplest logical elements and ending with processors and gate arrays (FPGA). Of course there also are lots of IC manufacturers offering IC’s. Many of them are specialized and wont be reviewed here. Lets limit ourself to smaller more general digital chips basically TTL 74series . This series is produced by many manufacturers like Texas Instruments (TI).
Common marking:

Manufacturer identifier indicates the manufacturer name;

Family – also indicates a temperature range:

• 74 – commercial (0…70°C), while CMOS chips has a range of (-40…+85°C);

• 54 – military where working temperature range is (-55…+125°C);

Series code – up to three symbols:

• none – standard TTL;

• LS – Low power Schottky;

• S – Schottky TTL;

• ALS – Advanced Schottky TTL;

• F – Tast TTL;

• HC- high speed CMOS;

• HCT – High speed CMOS with TTL inputs;

• AC – Advanced CMOS;

• ACT – Advanced CMOS with TTL inputs;

• BCT – BiCMOS technology;

• ABT- Advanced BiCMOS Technology;

• LVT – Low Voltage Technology with low voltage power source;

Identifier of special type – two symbols that can be excluded;

IC type – IC type describing its function;

Package type:

• N – plastic DIL (DIP);

• J- ceramic DIP;

• T- flat metal.

For instance SN74ALS373, SN74ACT7801, SN7400.

This is fun project I found on Jon’s antique radios web-page. He has managed to convert VGA output signal from PC to X Y X oscilloscope signal. Converting VGA RGB signal to synchronized oscilloscope input signal is pretty easy because VGA has two sync signals separate from RGB signals. Look at pin-out of VGA cable:

Sync signals makes things much easier as there is no need for additional sync signal generators – thus circuit becomes pretty simple without any programmable components:

The sync signals taken from VGA cable triggers sweep tooth signal (555 timer) generators. These generators generates ram signals for oscilloscope, that enable creation of raster pattern. The vertical generator frequency is around 75Hz and horizontal about 35kHz is used as horizontal sync pulses. Output sync (75Hz) is fed to oscilloscope Y-axis and and 35kHz sync signal is fed to X-axis of oscilloscope. The circuit is ready for 800 x 600 at 75Hz refresh rate. For different configurations you might need to adjust horizontal and vertical sync 555timers RC circuits.

RGB signal is converted to monochrome signal and fed to Z-axis of oscilloscope as intensity.

Inside the box:

Be sure that you turn PC before switching oscilloscope ON otherwise without PC sync signal you will get bright dot on Oscilloscope screen what can burn the phosphor. When turning off – turn oscilloscope first before turning off PC.

Circuit is sensitive to voltage swings. Be sure that you have stabile +5V.

PC desktop image:

The image on oscilloscope:

References: Jon’s antique radios.