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Covox Board – 8 Bit Audio not only for Legacy Computers

The 80’s called: they want their audio back…

That’s what happens when you’re drinking a few beers and being in a nostalgic mood: Already over a year ago I had designed a generic Covox Breakout Board (Wikipedia link) based on an old well established design.

Covox Board PCB

The whole design is based on two TTL ICs (74HCT373 and 74HCT164) and an R-2R resistor ladder (7.5k and 15k Ohm). The result is a simple DAC with 8 bit parallel and serial input and a few control pins. I’ve uploaded the PCB (back then I still used Eagle Cad) and the Gerber files to my Github Covox Repository.

Sure, I could have taken a cheap audio DAC, address it for example via SPI, and let the dedicated chip do all the heavy lifting. But that would not have been half of the fun of designing the board and (bit)banging the audio signal… 😉

The design is pretty generic and when I built it I thought I could use it in combination with a Sharp PC to generate audio output. I started with a few lines of code, but in the mean time other private tasks became more important. So I’ve reduced my testing of the Covox card to connecting it to an Arduino board and output simple (square and saw tooth) waveforms on my oscilloscope. Maybe if there is enough interest I will try to create a video with some mod-tracker like audio output…

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RANT: Do not misuse spreadsheets for data storage

Using spreadsheet files for data storage and exchange can lead to the
corruption and even loss of information — sometimes without noticing it immediately. I came across this one too often so I could not help but write a rather long post about this topic.

Sharing datasets with other researchers or collaboration partners is a vital part of the knowledge exchange in a community. This might happen in big scale in form of supplementary material along with publications or in small scale within research groups. In this post I do not want to focus on what is actually shared, but how. Because a crucial but commonly underestimated element when sharing datasets with others is the used data format. Continue reading “RANT: Do not misuse spreadsheets for data storage”

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WD PiDrive Cable USB 3 to USB 2 Hack with a Saw

I literally wanted to start this post with “I literally hacked the PiDrive cable…” but I actually have sawn it instead. Duh!

I’m using quite a few Raspberry Pi boards as servers, gateways, etc. and recently started to ‘polish’ their design. Instead of hard drives hanging beside them with a bunch of loose cables I’ve started to buy WD PiDrive Cases and Cables to pack all of them into nice ‘little boxes’.

The PiDrive Cables are really neat: they are designed to be positioned between a Raspberry Pi, its power supply, and an USB hard drive. The cable is designed for USB 3.0 hard drives, but in one case (hah) I wanted to use an external USB 2.0 drive I had lying around. So without further ado I’ve removed the USB 3.0 extension of the connector with a saw. It looks crude but works perfect…


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Aliexpress search customization and optimization (via hidden sort options in the URL)

About a year ago (2016) Aliexpress decided to cripple simplify their search engine. They’ve removed really useful search options and added (at least in my eyes) unnecessary ones.

These useful search options were removed from the search panel but they are still available as URL parameters. I’ve mainly written this post to document these missing options for my everyday searches — but I’m pretty sure others may find them useful as well.

Aliexpress Hidden Search Options
Parameter Declaration Description
isUnitPrice y Show Price per Piece
minQuantity value Minimal Quantity in Lot
maxQuantity value Maximal Quantity in Lot
minPrice value (e.g. 1.23) Minimum Price
maxPrice value (e.g. 9.87) Maximum Price
isFavorite y Results with 4+ Rating
isFreeShip y Free Shipping only
sortType price_asc/price_desc Ascending/Descending Prices
shipCountry de/us/… Destination Country
shipFromCountry cn/de/us/… Country of Origin

Especially the option isUnitPrice is helpful when searching for the best price per piece and not price per lot. I really cannot understand why this option is not available per default.

So when I’m searching for the lowest price per piece within a certain quantity range (here: 10 – 50 pieces) with free shipping I would add to the URL (Example Search):

&minQuantity=10&maxQuantity=50&isUnitPrice=y&sortType=price_asc&isFreeShip=y

Side Note: It also makes a difference which keywords you are using when searching. The following three searches will (at least the last time I’ve checked) give different results:

  • “stm32f103c8t6 lqfp“
  • “stm32f103c8t6 lqfp48“
  • “stm32f103c8t6 lqfp-48“

So even slight variations can make a big difference. Unlike the search on eBay, the search on Alibaba and Aliexpress does not split up keywords into smaller ‘chunks’ which are used for searching.

2018-08-02: Updated the List of Search Options

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Windows 10 Update can brick a Dual-Boot Setup when using Primary Partitions only

TL/DR: Use extended partitions for Linux in a dual-boot setup with Windows 10 — otherwise you might not be able to boot after a Windows update.

A few days ago I had to fix a dual-boot setup consisting of a Windows 10 and a Linux (Ubuntu) system. After deploying the latest Windows 10 Anniversary Update neither Linux nor Windows was accessible anymore. Only the GRUB rescue prompt appeared:

error: unknown filesystem.
Entering rescue mode...
grub rescue>

GRUB wasn’t even able to manually boot into the Windows or Linux partition. Continue reading “Windows 10 Update can brick a Dual-Boot Setup when using Primary Partitions only”

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Started to build my Raspberry Pi PiDrive System (for RetroPie)

I’ve started to rework my Raspberry Pi ‘dial-up’ interface. Instead of just handling my external VPN and SSH connections I’ve extended it to also function as an intermediate file server and Git repository (both via NFS+SSH). I’ve also inserted the Raspberry Pi into a new case and added a 1 TB 2,5″ drive. I think it can handle additional load so I plan to extend its capabilities to also serve as a RetroPie console.

By the way: the case and the connector cable between the drive and the Pi are both from WD Labs. The hard drive is not a PiDrive but a refurbished USB 3.0 1 TB disk (it was a recertified My Passport Ultra) before I’ve dismantled it. For me it was cheaper that way. If you’re looking for a similar setup and need an additional power supply and SD card maybe you should think about buying a Nextcloud Box (free shipping; handled by WD). You might not need to use its ‘cloud’ functionality but still get all hardware I’ve previously mentioned which I think is a pretty good bargain.

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USB Infrared Toy (Dangerous Prototypes) free PCB build

I finally completed the free USB IR Toy v3 PCB I got over a year ago (May 2015) from Dangerous Prototypes.

It took so long because I had to order some of the parts from Digi-Key – and I wanted to wait until I’ve a longer list of parts to order.
I’ve used a PicKit 3 to program the PIC microcontroller. The trickiest part was finding the setting to power the USB IR Toy with the programmer. (I could have powered both devices via USB, but only had one appropriate cable at my hand at that time.)

usb-ir-toy-programming-verification

So far I’ve only verified that the USB IR Toy is detected as serial device and shows its version number in a terminal window. It looks like the build was successful… 🙂

usb-ir-toy-terminal-v222

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Kids + Railway Toilets = Toilet-Blinkenlights…

Today my kids impressed me by repurposing/hacking/misusing the toilet-occupied-light to send (morse-like) signals across a railway car. Their fingers were thin enough to press the micro-switches in the doors which normally would signal a locked door (i.e. occupied toilet). Not sure if someone noticed the strangely flashing lights… 😀

railway-toilet-door