How to solder SMD at home-Part one

Soldering SMD parts isn’t hard task and there are many methods of doing this. Lets go through several SMD soldering methods and examples. Method 1 For this you will need: Good eyes or magnifying glass. Better one and another; Soldering iron with small tip ~10W; solder wire with diameter about 0.6mm Steps to follow: cut solder wire in pieces in length of element width:  

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How PCB files are transfered to circuit boards

When you are done with “clean” period of task – designing, drawing a circuit and tracing a PCB, you need to transfer a design to a real board. Here starts what I call a “messy” part of design. When designing at home there are several options – to use prototyping boards or make PCB by yourself. In second option you have to transfer PCB image to board with copper layer. There are several methods of doing this: direct transfer with glossy paper where image is printed with laser printer or use more advanced ultraviolet exposure. This way PCB image is printed on paper or film directly from program window without keeping in mind about pcb file formats. Different situation iswhen fabricating professional PCB’s. Each company which fabricates PCB boards always announce what type of file formats they support. So if you are going to order a PCB better check with them in order to save your time. The most common and standard format is so called Gerber file format. Almost all layout tools are able to produce Gerber files. If you want to preview your generated Gerber files there is a nice free Gerber file viever(GCPrevue) from GraphiCode, Inc. (http:\\www.graphicode.com)…

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PCB routing considerations

One of hardest tasks when fabricating PCB’s is Printed Circuit Board(PCB) routing. There is no unified rules on how properly board should be routed and it would be impossible to write them as situation on each board is different. One of general rules are that the shortest routes are the best because longer routes tend to generate more noises or pick them up from different sources. It is obvious that every conducting material acts as an antenna no exception with PCB routes. No secret that each route acts as small transmitting and receiving antenna. So one thing is to keep in mid when routing PCB is to route short as possible. Another concerning area is a cross-talk or cross-coupling between routes. This effect appears when two traces run along each other and energy from one trace route couples to another. This effect is obvious in high frequency digital and analog circuits. This effect can make device dis-functional because only of crosscoupling effect. These defects are hard to determine as electrically circuit board is correct. If this effect is noticed – the only solution is to cut traces off and run separate wires instead. It is better to do keep this…

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How does tri-state buffers work

Those who work with microcontrollers probably know about data buses. Only one device(memory, peripherals), that are connected to bus can work at one moment. So only one unit can have direct connection to bus besides CPU which usually is a host. So decoding circuit determines the desired unit and connects it to bus. Other devices are effectively disconnected so that they wouldn’t have any affect to bus operations. They are carried out by tri-state buffers. Tristate buffers allow to isolate circuits from data bus. This means that circuit is switched to high impedance state. Usually we know dual state circuits that can have two logical levels “0” and “1”. But there is also widely used tristate logic, where is ability to switch I/O to high impedance state. Tristate logic can simply be made by two transistors:   Using such circuit we can have following output results according to input variations:   Q1 Q2 Output OFF OFF High Impedance OFF ON 0V ON OFF +5V   Simply speaking when output pin is in high impedance state it is physically disconnected from circuit.  

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Using Gray code for rotary encoders

Gray code is well known and widely used in angular movement systems where angular positions has to be known. Gray code encoder can be constructed pretty easily by masked wheel where tracks are read with photocells.   Did you look at the picture and thought for yourself that gray code is same binary code. Well no… main problem with binary system that using binary code in tracks there are many positions where several tracks change state at same time. This may result in error. Actually in gray code only one track can change at same time during rotation. So then if error occur, the resulting erro will be only one bit. Gray code is easy to convert to binary this task can be done by any microcontroller using a lookup table:     Also you can convert Gray code to binary analytically. To convert from binary to Gray, start at the MSB and compare it to 0. If MSB is equal to0, then write 0 as the MSB for the Gray coded number, otherwise write 1. Next compare the next MSB and compare it to the MSB. If they are equal write a 0 in the position for the Gray…

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Nonlinearity and span of transducers

Every time when developer is selecting a transducers for their projects they have to look through various parameters and select part which best fits the design needs. This time lets look at some transducer characteristics that can be found in specifications. Transducer Range First of all lets clear out what is a range of a transducer. Range is understand as maximum and minimum input and output signal. For instance we can take simple thermal sensor which input range can be from -50 to 120ºC and output range of 0 to 5V. Range can be understand not as only measured signal range but working environment parameters like working temperature range, power supply voltage range etc. Full scale deflection – Span Span is the maximum variation in the input or output. Span can variate due an error that mostly is linear and can be adjusted. Span error is measured in percents which shows how much the output value is different from correct value.   Another linear error close to span error is zero offset. This error occur because of calibration errors or other changes like aging or environmental conditions change. Zero offset error is constant over all range. It can be fixed…

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X-10 interface for home automation projects

Simply speaking X10 protocol allows transmitting data over power lines. X10 uses a PLC(Power Line Carrier) technology. How does this work? Specification says that each time 60Hz AC signal crosses zero line there is a 120kHz burst transmitted with duration of 1ms.   One crossing burst forms one information bit. Simply speaking if wee need to form “1” you need to burst at first crossing but nont at second and for “0” is reversed pattern – you need to burst at second cross but none on first.

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