Calibrate a magnetic sensor


Liudr shared a how-to on calibrating a sensor:

First of all, what is calibration? In a general sense, calibrating a sensor makes the sensor provide the most accurate readings allowed by the sensor’s own precision. As an example, let’s assume for a moment that the earth’s magnetic field and any other stray magnetic fields are shielded and you have a uniform magnetic field generated artificially for the sole purpose of calibration. Let’s say that the field strength is 400 mG (milliGauss), equivalent to 40,000 nT (nanoTesla). Now if you align one axis of your magnetic sensor parallel to the direction of the field, it should read 400mG. If you then carefully rotate your sensor so that the axis is anti-parallel with your field, it will read -400mG. If you didn’t do a good job in either alignments, you will read less values, say 390mG, if you’re off by about 13 degrees, because only a portion of the field, which is a vector, is projected along your magnetic sensor’s axis.

See the full post on Liudr’s blog.

App note: Overcurrent event detection circuit


Sample overcurrent detection circuit from Texas Instruments. Link here (PDF)

This is a unidirectional current sensing solution generally referred to as overcurrent protection (OCP) that can provide an overcurrent alert signal to shut off a system for a threshold current and re-engage the system once the output drops below a desired voltage lower than the overcurrent output threshold voltage.

App note: Active filtering in automotive audio applications


App note from Texas Instruments on isolating DC and high frequency noise in audio using their automotive op amps. Link here (PDF)

Phone calls, emergency alerts, and music are just a few of the reasons that a high quality audio system is vital in automotive infotainment and clusters. Operational amplifiers (op amps) are one of the most common building blocks of automotive audio circuits. Many designers choose to incorporate op amps into their automotive audio circuits in order to increase audio performance. Higher order filters, which can be created through a combination of second order filters, attenuate noise more aggressively than lower order filters. Additionally, active filters remove the chance of unwanted interference with the audio signal.

CurrentRanger: auto-ranging current meter


An auto-ranging nanoAmp meter from LowPowerLab:

CurrentRanger is a nanoAmp current meter featuring auto-ranging, uni/bi-directional modes, bluetooth data logging options and more.
It is a highly hackable and affordable ultra low-burden-voltage ammeter, appropriate for hobby and professional use where capturing fast current transients and measurement precision are important.

More details on LowPowerLab site.

Check out the video after the break.



Teardown of an Array 3711A 300W DC electronic load


Kerry Wong did a teardown of an Array 3711A 300W electronic load:

I have made many electronic loads in the past. For instance this simple harddrive cooler housed small dummy load, this more sophisticated constant current/constant programmable load and this heavy-duty electronic load that is capable of sinking over 1kW under peak load. In this blog post though, I am going to take a look inside an Array 3711A DC electronic load I recently purchased on eBay. You can find a video of this teardown towards the end of the post.

See the full post on his blog here.

Check out the video after the break.

Simple homebrew 6502 computer


Sven Krasser blogged about his 6502-based homebrew 8-bit computer build:

After completing my VGA Generator project a while back, I’ve embarked on a new electronics project: building a simple 6502-based homebrew 8-bit computer on a breadboard. There are a bunch of similar projects online from which to draw ideas. Some projects set constraints such as only using contemporary parts of the 8-bit era, no FPGAs, no microcontrollers etc. In my case, I opted instead to keep the constraints minimal and the project simple.

See the full post on his blog here.

Check out the video after the break.

Making an e-Paper Etch-a-Sketch


Scott Baker has been working on making an Etch-a-Sketch using modern e-Paper displays and optical encoders:

Above you can see my prototype. I’m using a 4.2″ e-Paper display from Gooddisplay, together with the Waveshare breakout board. I have a couple of ENS1J-B28-R00128 optical encoders that I attained on eBay. I specifically chose these encoders instead of traditional electro-mechnical encoders due to the high numbers of pulses per revolution. A typical electro-mechanical encoder will net about 24 pulses per revolution. The optical encoders I bought on ebay are 128 pulses per revolution. Our 4.2″ ePaper has 400×300 pixels. To traverse the major axis would require 16 full turns of the electromechical encoder but only 3 turns of the optical encoder.
The hardware is so simple that there’s not much more to say. The encoders are connected to GPIO pins of a Raspberry Pi. Note that there are resistors inline on the encoder outputs as the encoders are 5V and the Raspberry Pi uses 3.3V GPIO. The e-ink display is connected to the SPI bus.

See the full post on his blog here and the GitHub repository here.

Check out the video after the break.

App note: Blood pressure monitor fundamentals and design


Application note from NXP on blood pressure monitor fundamentals using their medical oriented MCUs. Link here (PDF)

Arterial pressure is defined as the hydrostatic pressure exerted by the blood over the arteries as a result of the heart left ventricle contraction. Systolic arterial pressure is the higher blood pressure reached by the arteries during systole (ventricular contraction), and diastolic arterial pressure is the lowest blood pressure reached during diastole (ventricular relaxation). In a healthy young adult at rest, systolic arterial pressure is around 110 mmHg and diastolic arterial pressure is around 70 mmHg.

App note: How to eliminate over stress of MOSFET during start-up of flyback converter


App note from Richtek about their embedded soft-start function to eliminate MOSFET stress. Link here

Switching Power Supply, compared to Linear Power Supply, is widely used due to its advantages, such as small size, light weight, high efficiency, etc. Flyback Converter, one of the switching power supply topologies, is most suitable for power supply systems that are below 150W because of its unique features of isolation between primary and secondary sides, simple circuit architecture, few components, low cost, etc.

Since switching power MOSFETs play a very important role in switching power supply converters, how to effectively eliminate over-stress of MOSFET during the start-up of flyback converters will be the main focus to be discussed in this application note. The three major aspects to be investigated are flyback controller design, feedback stability, and Snubber design.

Grbl_ESP32 development board version 3.1


A board to control your CNC machine with Grbl_ESP32 designed by Bart Dring, that is available on GitHub:

This is a Grbl_ESP32 CNC Development board. This is a quick and easy way to use and test CNC on the ESP32 controller.
Grbl is a great CNC firmware that has been around for nearly a decade. It was originally designed for the Arduino UNO and basic 3 axis CNC routers, but it has been ported to other CPUs and was the basis for many other CNC and 3D printer firmwares.
The firmware was written using the Arduino IDE to make it as user friendly as possible. If you have experience with Arduinos, this will not be much different.

Project info at Buildlog.Net Blog. It’s also up on Tindie.