Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

I've received the Minleaf NPS3010W 110V/220V Digital Adjustable DC Power Supply from BangGood recently and I'm happy to say that this is an item that's really worth having in your toolkit if you do any sort of hobby electronics work. It's a nice and compact DC power supply that can provide up to 30V at up to 10A. It even has a readout showing how much power you're drawing (in W). That's a quick summary, now lets get into some more details.

First the packaging. There's nothing fancy here, but it doesn't need to be. The power supply comes in a thin cardboard box. Foam padding is used to protect the item in transit, and the power supply itself is also packaged in a plastic bag. The AC mains cable and the DC alligator clips are just in the box, together with the manual.

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Last year I wrote about Reading console output from the E200 Allwinner based Video Brochure and promised that I'll have another update about how I got the brochure to work on external power and with reset/looping circuitry added. Time slipped by since then but here's that update, finally.

First lets take a step back though. It all started when I wrote about Hacking the VideoPak 7inch promotional brochure to work as a digital photo frame. In that article I was able to get my own images (as videos) to display on the device, but also noted - So far so good, but unfortunately every time the device shut down after the last video has been played. Well I just could not let go of this project and not having reused the brochure in some way would have been a total waste of resources used to create it.

What I needed to do was somehow force the magnetic switch to trigger when the device finished displaying all of the videos. Since the device would turn off once all of the videos have been displayed, its screen would be off too, so I figured that I could make use of that. After looking around and probing the controller board, I found that a 6 pin chip labelled B1B86j (apparently a DC voltage regulator) had one of its pins fall from high to low whenever the backlight to the screen was turned off. This gave me an idea. I could monitor this pin and then when I detected it going low, I could do something on the magnetic switch side.

On the magnetic switch side I noted that it would usually be pulled high when videos were running. It wasn't enough to pull it low to trigger however, I had to pull it low, then pull it high. When that was done, the device would reset. Progress!

I still had the issue of what to do with regard to power. The micro-USB connector that was part of the brochure had undesirable behaviour - whenever power or a data connection was made, the device would go into charge or external USB storage mode and would not display videos. This meant that I couldn't simply connect external power to this port and be done with it and since I had no way of changing the firmware, I was forced to find another way around this.

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I've been using Macs for work for at least the last ten years and for many years on my current project I've been using a company managed Mac that I owned. We recently had some changes in policy, and due to new security requirements I could not use the Mac that I had been using previously. So, I was issued a new Mac for the project, which of course meant setting up front scratch and copying the dozens of gigabytes of data over. Luckily this is relatively easily done using target disk mode ...and a USB-C to USB-C cable.

Now I could have done something like enabling SSH on my old Mac and transferring files using scp. Or I could have set up an FTP server and transferred files that way. I could have also copied files over to an external disk. None of these methods are particularly elegant and require either additional hardware or software to be installed.

Using target disk mode (TDM) means you can use the USB-C charge cable that came with your Mac to connect both Macs together and easily copy files from one to the other. Enabling TDM is done by first shutting down the Mac you want to copy files from. Then while holding down the T button, power on the Mac.

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The Mac will not start macOS, but will start up as if it was an external disk drive. You will see the Thunderbolt symbol on the screen once the Mac you're copying to has connected to it. It may be necessary to enter the HDD password to unlock the source Mac, if you're using an encrypted file system.

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While looking around one of the servers at work I noticed that the application account I was logged into had an odd file in its home directory. The file was named "-rw-r-----.". This was obviously something that went wrong and I decided to remove it. However when doing the naive thing and simply running the following command results in an error...
$ rm "-rw-r-----."
rm: invalid option -- 'w'
Try `rm ./-rw-r-----.' to remove the file `-rw-r-----.'.
Try `rm --help' for more information.


The issue arises because the file name starts with a dash character. The correct (and error free) way to remove such files is to use the -- command line argument with rm first like so...
$ rm -- -rw-r-----.


No errors!

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