NFC antenna tuning without a VNA


Fred writes:

Recently I started work on a new board. This one will be a front door entry system, so I decided to go with something that could read my NFC implant but also had a numeric keypad for the kids (and anyone else) to use. Not everyone wants to be chipped. Crazy, isn’t it? I’ll write more up on the board when it gets closer to completion, but for this post I’m going to concentrate on a small PCB antenna that’s intended for use with a tiny implanted tag. I’ve successfully used a wirewound inductor before, but I decided it was time to try a PCB trace antenna. This is the most common way to make an NFC reader, but nobody seems to have tried to tune one for an implant – probably because it means it will be worse at reading larger tags. Anyway, this is about creating a small PCB antenna and more importantly tuning it so that it read well.

Check out the video after the break.

More details on 0xFRED blog.


App note: Securing vibration motor leads and wires


App note from Precision Microdrives on how to properly connect wires on to vibration motors for reliability. Link here

Vibration motors require electrical power, which must be delivered by wires or PCB tracks to the motor. Precision Microdrives vibrating motors are available in a range of connector forms. From stock, they are available with factory installed leads, terminals, PCB solder pins, or as PCB SMT / SMD options. Solder pins and SMT motors have the advantage of being mounted directly onto the PCB which simplifies the connection process.

App note: Vibration Motors – Voltage Vs Frequency Vs Amplitude


All about vibration motors and how its frequency and amplitude be controlled in this app note from Precision Microdrives. Link here

We’re often asked how to adjust the vibration amplitude or frequency of our various vibration motors. In this article, we’ll look at how simple it is, why it can be useful, and how we can predict the behaviour of a motor using the driving voltage and Typical Performance Characteristics graph.

An Arduino version of Brooks Shera’s GPSDO


Jeff (aka K6JCA) has a great write-up on implementing the Brooks Shera Phase-Locked Loop GPSDO on an Arduino Platform:

This blog post is a continuation of my two earlier GPSDO blog posts. The first one (from a few years back) details a simple Frequency-Locked Loop GPSDO design, based around an Arduino processor. The second (more recent) blog post discusses simulating Brooks Shera’s GPSDO algorithm (from the July, 1998 issue of QST) using The MathWorks Simulink program.
This third blog posts describes my modification of my original Frequency-Locked Loop (FLL) GPSDO to be a Phase-Locked Loop (PLL) GPSDO, and it includes the hardware schematics, Simulink models, and the Arduino code I wrote to implement Brooks Shera’s GSPDO algorithm on an Arduino processor.

More details on K6JCA blog.

App note: MELF resistors – The world’s most reliable and predictable, high-performing film resistors


App note from Vishay on why MELF resistors are so successful and has no alternative in today’s application. Link here (PDF)

For more than 25 years, Vishay’s MELF resistors have successfully met the demanding requirements of the automotive industry. They offer superior SMD resistor performance in terms of accuracy, stability, reliability, and pulse load capability. The cylindrical construction of MELF devices provides an optimal power rating and pulse load capability related to the mounting space. Continuous development has led to improved long-term stability and moisture resistance, and allows high-temperature operation to + 175 °C.

Serial Star, a 4 in 1 USB serial and I2C converter


Jesus Echavarria published a new build:

Here’s one of the last board I design the last year. On 2016, I develop the Dual USB Serial and I2C Converter board. Although this board works fine, it has a couple of lacks. First one, is that to use the both converters, you need two free USB ports. Is a minor problem today with USB hubs, but you need the hub and also two USB wires. And the other problem is that this board uses mini-USB connectors. Of course today you can still find it, but aren’t as common as the micro-USB wires. For this two reasons, I decide to upgrade the board, add the micro – USB connector and put a USB hub inside it. Because I choose a 4-port USB hub, I use also 4 USB serial converters. With some addons, you can select power supply value (5V, 3V3), serial levels (TTL, RS232) and GPIO functions in an independent way for each converter. So, let’s see how works this USB Serial Star, a 4 in 1 USB to Serial and I2C Converter.

More details on Designing Electronics in Spain blog.

Teardown of a Piezoelectric vibrating gyroscope


Kerry Wong did a teardown of an old analog piezoelectric vibrating gyroscope:

Gyroscopes nowadays are based on micro-electro-mechanical systems (MEMS) technology. They are low cost and extremely miniaturized. A device combing both a three-axis gyroscope and a three-axis accelerometers (sometimes these devices are referred to as 6DOF devices) such as the MPU-6500 for example can be had in a QFN package as small as 3 mm x 3 mm and under 1 mm in height. Before these MEMS devices gained mainstream popularity however, larger piezoelectric vibrating gyroscopes were used in many consumer electronics devices.

See the full post on his blog.

Check out the video after the break.

Solar powered weather station

Solar Powered Weather Station-600

Antalife has written an article detailing the build of his a solar powered weather station:

To expand my microcontroller and programming knowledge I have decided to try and make a Solar Powered Weather Station. My goal is to record parameters like:
*Air pressure
*Air quality (something to do with CO or CO2)
I then hope to send (wirelessly) the data to a base station and log/display it on a simple website. To make things interesting I also aim to power the data gathering station from a large supercapacitor (~100F), and in keeping with my solar tradition the supercapacitor will be charged from a solar-cell.

See the full post on his blog.