Making a SPL dB meter

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Shawon Shahryiar over at Embedded Lab shared a how-to on making a SPL dB meter:

Sound needs a medium for propagation or travel. It can’t travel in vacuum. Normally air is that medium but sound can also propagate in liquids and other states of matter. I am not going to lecture on how sound travels and its properties as Wikipedia details everything well here. Everything we see around us has a measurement and a unit. In case of sound pressure, the unit is decibel. Our basic requirement is to be able to measure Sound Pressure Level (SPL) in decibel scale with a typical 8-bit microcontroller, an ordinary microphone and without involving complex algorithms.
Measurement of sound has a number of uses. For instance, monitoring sound pollution, security system, monitoring the quality of an amplifier, detecting sound profile of an environment, etc.

Building your own 555 timer IC

555 Timer IC

The classic 555 timer on a breadboard:

Here, I will show how you can make your own version of the 555 timer using just NAND gates, opamps , a transistor and a few resistors! Now, you may think what is the purpose of building this when you can buy the IC at very cheap rates. The answer is, you learn electronics better, understand how the actual IC functions and improve your confidence in building electronic circuits.

More details on TheMagicSmoke blog.

Edge-lit seven segment display

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Debra over at Geek Mom Projects posted detailed instructions of how to build this edge-lit seven segment clocks:

This build combines small dozens of small laser-cut acrylic pieces which fit together with very tight tolerances. It uses skinny (4mm wide) LED strips which must be soldered, bent, and then slotted in between those acrylic pieces. When assembling the parts you must be willing to force pieces into place, even though it feels like you are stressing the brittle acrylic. You must also be willing to remove and re-seat said pieces and LED strips when it turns out they *can’t* actually be forced into place. At some point during the assembly there is a strong likelihood that you will have to remove everything and re-solder your LED strip when you realize that forcing everything into place broke one of the wires away from your LED strip or created a short circuit.

See the full post on Geek Mom Projects blog.

Check out the video after the break.

Minimal ATSAMD21 computer

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Johnson Davies shared detailed instructions of how to build an ATSAMD21-based computer on a prototyping board using a 32-pin ATSAMD21E:

If you’re looking for something more powerful than the ATmega328 in the Arduino Uno a good choice is the ATSAMD21. This is an ARM Cortex M0+ processor with up to 256KB flash memory, 32KB RAM, and a 48MHz clock, so it’s substantially better equipped than the ATmega328. In addition it has a USB interface built in, so there’s no need for a separate chip to interface to the serial port.
Arduino have designed several excellent boards based on the ATSAMD21, such as the Arduino Zero or smaller-format MKRZERO. However, these boards are an expensive way to use an ATSAMD21 as the basis for your own project, and they probably include many features you don’t need.

More details on Technoblogy.

Wifi based DIY 5V switcher for led-lights

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Albert posted a detailed how-to on building DIY ESP-12F based USB-5V switcher:

5V powered 100LED circuit was consuming around ~1.8Watts(though 5.1Ohm series resistor was really hot) and the brightness of the LED’s were not bad, especially difference between first led and last led brightness didnt bother me it was hardly noticeable when seen from distance. So I decided to use them as a christmas decoration for my garden.
I wanted to use them with battery-bank as there was no power-outlet readily available(for the safety of my children, i would avoid any 230v circuit in my garden especially in wet weather). Also I wanted them to be switchable remotely to avoid going out in the freezing cold. Hence this is what i came up with.. an “ESP-12F based USB-5V switcher”

See the full post on his blog.

So how to do CW on a homebrew SSB rig?

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Pete Juliano, N6QW, has written an article on how to do CW on a homebrew SSB rig:

The Answer is Not a Flippant: Carefully!
Author’s note: A friend in VK4 land made an inquiry about CW operation. I find that 99.99% of my operating time is SSB. But others spend a greater time on the air using CW so why not share some info and data that I have stashed on my computer where a SSB rig can be made to work CW. This also open the possibility of filter switching for a more narrow pass band. With Arduino anything may be possible.

More details on Pete Juliano’s (N6QW) blog.

Remote debugging with USB based JTAG/SWD debug probes

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Erich Styger wrote an article on how to turn a USB debug probe into a IP-based debug solution:

For some projects it is not possible to have the device under debug available on my desk: the board might be in another room, on another site or in a place where physical access is not possible or even dangerous. In that case an IP-based debug probe (see Debugging ARM Cores with IP based Debug Probes and Eclipse) is very useful: as long as I can access its IP address, that works fine. It is an excellent solution even if the board is moving or rotating: hook it up to a WLAN access point and I still can use it as it would be on my desk.

More details on MCU on Eclipse homepage.

ATtiny13 – 8bit mono class D amplifier

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Łukasz Podkalicki shared a how-to on building a Class D amplifier on ATtiny13:

I always wonder whether it is possible to make an amplifier of class D on ATtiny13 or not. Some time ago I found George Gardner’s project based on ATtiny85 – TinyD. It was a sign to start challenging it with ATtiny13. It took me a few hours but finally I made it! The code is very short and useses a lot of hardware settings which has been explained line-by-line in the comments. The project runs on ATtiny13 with maximum internal clock source (9.6MHz). It gave me posibility to use maximum of hardware PWM frequency (Fast PWM mode).

See the full post on his blog.

Check out the video after the break.

Outdoor UV index sensor

Outdoor UV index sensor

A detailed instructions of how to build this outdoor UV index and ambient light sensor from Mare & Gal Electronics:

The VEML6075 senses UVA and UVB light and incorporates photodiode, amplifiers, and analog / digital circuits into a single chip using a CMOS process. When the UV sensor is applied, it is able to detect UVA and UVB intensity to provide a measure of the signal strength as well as allowing for UVI measurement.