Posts

After finally getting my Cetus3D MkII 3D-printer I was eager to start to print. When I started through the steps to calibrate the printer by adjusting the build plate height, but the print head/nozzle refused to get close enough to the build plate to finish the calibration! The cables on the motor came in contact with the chassis of the printer! So the injector was 5mm from the build plate and couldn’t get any closer by increasing the step values. But there is an easy fix for the problem. ...

 ITEAD contacted me about testing some new equipment and write an unbiased blog post about it. I usually reject all such offers, but this one worked for me. Why? Well, all the stuff they offered was on my shopping list anyway! And my home is quite literally chock full of Sonoff relays, lamps, etc. So the first thing I started to play with was the SONOFF RF BRIDGE 433. The bridge makes it possible to control switches, doorbells, curtain openers, etc. that uses 433MHz communication frequency. I’m not interested in using the original firmware because I prefer to do my home automation setup in Node-RED. Here’s how it works. ...

Over the years I’ve been reading about a way of restoring old computers and other equipment where the plastic has turned yellow and how some bright guys developed a method called Retr0bright to reverse the process. The reason for the yellowing of the plastic is the flame retardant bromide that is infused in the plastic to prevent fires. When exposed to UV-light, the bromide comes to the surface of the ABS plastic, and the yellowing begins. Unfortunately, even after treating the item with Retr0bright, the yellowing returns after 3-4 years, looking worse than your grandfather’s underwear. Here’s my attempt at a fix to that problem. ...

[caption id=“attachment_5818” align=“alignright” width=“300”] My first attempt of a Collinear Antenna. Professional mounting![/caption] Part 1 – Checking the Velocity Factor of the Coax Cable I have a homebuilt Collinear Antenna on one of my two ADS-B receivers. It’s an eight element antenna, built without any real effort of making sure that all the elements where the right length. So it’s about time to try to do it properly. The easy way is to get Flightaware’s great ADS-B antenna and filter, but it’s fun to build your own as well. To build a good antenna, you would preferably use a Vector Network Analyzer so you can do proper measurements of your antenna design. With it you can quickly check stuff like SWR and optimize the impedance of the antenna at the frequency it’s intended to be used. In my case 1090MHz for ADS-B. But if you don’t have the money to spend, you have to improvise. I’m going to build a 12 element Collinear Antenna out of cheap RG-58 coax cable. But to calculate the right length of each element, we need to know the Velocity Factor, or the signal speed through the cable compared to light traveling in a vacuum. So let’s do the measurements. ...

If you are on the lookout for a sub $30 Multimeter (or $15 on eBay) for working with low voltages, the best one right now in my opinion is the cute and tiny Aneng AN8008 TrueRMS Multimeter or the newer model, the Aneng AN8009 with NCV and temperature measurement. They have a lot of functions and can measure µA current, and both are a 9999-count meter. The continuity tester is reasonably fast, but there is one little problem that bothered me. It takes 5 to 10 seconds for it to settle on a correct voltage reading. When it finally ends, it’s spot on, but the waiting is annoying. But fortunately, there is a simple fix for this problem. ...

Finding System Files in Finder Don’t you hate it when you need to find a .plist settings file or any other file that is in one of the Mac OS system files folders? I do. So here is a little tip on how to do global system files search directly in the Finder. ...

Easy Way To Calibrate a Bryman BM869s Multimeter After replacing my lost Fluke 87V multimeter with a new Brymen BM869s (rebranded Greenlee in the US) about a year ago, I’ve been delighted with the multimeter. It has every possible function I could ask for and then some. It’s been my go-to meter when working on electronics projects. I do have a Siglent SDM3055 DMM that is very good, but due to its startup time, I usually reach for my Brymen BM869s when I need to measure something, and it has higher resolution. But after getting a broken HP/Agilent 34401A DMM from eBay, fixing it up and replacing all the capacitors, I now have a better reference. I’ve compared it to my friend’s calibrated 6 ½-digit multimeter, and it’s still within spec, so naturally, I want my Brymen to be as close to my HP 34401A as possible. Turns out that calibrating and adjusting the Brymen is quite easy. Here’s how to do it. ...

Can’t Remove Purgeable Disk Space Note: If you have MacOS High Sierra installed, you need this guide instead. When trying to install Bootcamp on my MacBook Pro, I had to delete a lot of files to get enough space to be able to accommodate for a Bootcamp partition on the drive. But even after removing around 60 GB of storage, MacOS Sierra could still not make a large enough partition for Windows. When checking with Disk Utility, it showed that indeed I had enough space, but there was a part called Purgeable that was impossible to move. No tools from Apple are available to handle this, but here’s how I fixed it. (not actually my disk, forgot to take a screenshot) ...

My wild guess is that most people get a small Linux computer, like the Raspberry Pi, BeagleBone, Banana Pi or Orange Pi for a specific task. Unfortunately, most distributions are chock-full of software, with everything installed per default. But if you want to set up a lean single board computer for a specific task, you’re out of luck. Thankfully there is a Linux distribution, DietPi, that aims to fix that problem. ...

When you make your own NTP server, you probably spend a lot of time trying to get it as accurate and stable as possible. To get good results, you need to connect your server to a good time reference, like an atomic clock, GPS or a GPSDO to get the PPS (Pulse Per Second) to sync your server with the reference clock. In both Linux and BSD, there is kernel support to slave the very inaccurate CPU clock crystal to the PPS signal, continually adjusting the frequency, because the crystals of computers continuously drift due to temperature and barometric pressure differences. So most of the work is to get a crappy crystal to behave. What if you just jumped over that step, so the CPU clock gets synchronized with the same lab reference that the PPS signal uses, using a SI5351C Clock Generator? Read on to see a simple way of doing it and get an extremely accurate NTP server for under $200. ...