Ground fills and polygons – how to do this right in eagle

Take any professionally made PCB and you will find that in most cases areas between traces are filled with copper areas. In fact background fills can give benefit but also be harmful to your all design. Dangerous prototypes have written a tutorial on how to make MCB background fills look professional and add additional features to schematic. In most cases background fills are connected to GND in order to reduce resistance and electric noise. Keep in mind that filing grounds where ever it fits can also have negative effect – for instance ground planes near signal traces may add parasitic capacitance. In this case probably better use hatched fills or avoid them at all. Sometimes it is useful to draw custom ground planes around power traces to make them more thicker in order to carry more current.

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Hand written equation conversion to LaTex and MathML

Writing formulas and equations for some publication or websites is time consuming task. Usually there is LaTex syntax used to enter formulas. But when formulas get more complex it gets really hard to remember all short-codes and it is easy to loose end in a long line. At school we are used to write equations by hand so why not to transfer that experience in to computer. Here is a nice small script that simply converts hand written equation in to LaTex and MathML XML codes. All you have is to open a MyScript demo website and start drawing. Algorithm analyzes hand drawn formulas and tries to convert them in to code. It previews your progress so you could redo last steps to match your needs. I should say it does job really great. So if you do lots of formulas you may give a try – could be faster than typing.

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Electronic parts voice look-up assistant

As an electronic enthusiast, you probably have a pile of resistors, capacitors and other electronic components. Most of them are color coded, and to use any of these you need to identify each of them. Usually, resistor color band table works fine or multimeter. But how to speed up the process a bit, free your hands and even eyes from looking at charts or multimeter. Anthony coded a simple application (EEspeak) which listens to you what type of element and colors are identified. Imagine sorting things out – sitting around with the pole of resistors and reading each color values aloud. Voice recognition seems to work great without any training. It can tell color coded resistor, capacitor and inductor value with its tolerance. Simple commands enable it to read values aloud and display on the screen. The program is free so give it a try – at least it’s fun.

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12V solar charger using LM317

[Alex] decided to build a solar charger for his car battery. He had an 18V solar panel able to provide up to 83mA. You cannot connect panel directly to the battery because charging voltage cannot exceed allowed safe limit and also solar panel may become a load for battery in dark time, and this way discharge it. So he ended up with simple circuit utilizing LM317 and couple resistors setting voltage so that battery would be charged at recommended 13.2V. To prevent back supply, a Schottky was used. Of course, it adds some voltage drop (0.7V worst case). This was taken into account while calculating voltage adjusts resistor divider. As a test [Alex] left solar charger for three days connected to his battery, and it charged up to 12.35V which is about 75% of capacity. Not bad at all.

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Adding self power down functionality to your devices

Power down feature is convenient on battery operated devices. For instance, most of the multimeters already have this feature allowing them to self turn off when there is no activity for some time. Check out this simple solution which uses a pair of FETs and resistor. It was initially made for the Atmega328 project because the author didn’t want to bother with AVR power down modes. Instead, he used this simple circuit. It can be used to turn the device on with the switch. This is where the P-FET part plays a role and turn off with N-FET. Turn Off signal wire comes from AVR pin market as 5. While the device is powered N-FET has to be on with high gate signal. When N-FET gate signal goes low device turns itself off. This can be used on any device where possible to get such signal conditions. Or use in microcontroller circuit by adding some delay count after inactivity.

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OpenHardware RAM module for embedded projects

In more complex projects where audio or video are involved, microcontrollers usually run out of internal RAM. The only solution that stands out is adding external RAM. Depending on platform and solution used there are many ways of doing this. But usually goes SRAM modules, latch register(s) and probably some other additional circuits. If you only need to add more RAM without planning all this you can use RAM module like this one made by [Wardy]. This is simple RAM module with 512Kbytes of static RAM. It only needs 13 pins for interfacing and can accept voltage levels 3.3V or 5V. PCB layout is designed so that pins are breadboard compatible – easy to play with any microcontroller or dev board like Arduino.

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Avoid smoke with power protection circuit

When designing an electronic device you want to make sure that it won’t go in smoke under unexpected circumstances. You never know what may go wrong during the lifetime of the device especially if it is powered from mains. Jon Chandler made an excellent overview of standard and pretty simple power protection circuits that may help to avoid lots of trouble. The small circuit between your battery and device may protect it from mistakes like reverse power polarity. His lists start with a simple series diode which is cheap but may help protect from reverse polarity. Like any other, it has a downside – voltage drop (0.7V) that may be a pain for low voltage devices. The list continues with more smart solutions like Crowbar diode and fuse which avoids voltage drop but ends up with fuse blow on reverse voltage. Using MOSFET is a smarter way of protecting circuits. It gives a  smaller voltage drop – mV range with right MOSFET selected. This one is a common way used in many circuits. And of course, There are always specialized IC’s that provide way better protection. Like LTC4365 protects the circuit from reverse polarity but also from under and overvoltage.…

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