There are many advantages of the 1l mini PCs for home server applications: Obviously they are very compact, but more interestingly: The idle power consumption can be almost as low as current Raspberry Pi 5s acchieve, i. e. 5-6W*, all while avoiding many of their limitations**. In many cases the low power consumption is associated with quiet operation, which is especially important if you don’t have access to a dedicated server room in the basement or at least an acoustically isolated closet. Also, used mini PCs are available in large quantities at reasonable prices. This is why there is a ton of information and data out there, covering hardware expandability, compatibility with hardware and software and other aspects of converting mini PCs into capable home servers. ...

For quite some time I was looking for a rack to mount my 19" HP/Agilent gear in. I haven’t found a single rack that meets all my requirements. Most are too big, too small, too flimsy, too heavy, poorly made, too expensive, lack cooling … or are simply made for a different purpose. Since I already used IKEA LACK tables to put some of my 19" gear on - as a dodgy temporary solution - I thought: Why not build a little rack with those tables? A few screws later, two tables are combined into one ~45 EUR rack on four castors (IKEA RILL, 75mm). ...

The Technics SU-VX 700 is an integrated audio amplifier from the early nineties. It delivers 2x 90W into 8 Ohms and is specified with a THD of 0.007% (20Hz .. 20kHz, rated power). In my opinion it is one of the better Technics amplifiers. Whereas the sound of an amp is always subjective to a large degree there are some design aspects that are a bit more objective. What I particularly like about the SU-VX 700 is mostly related to its simplicity and repairability: ...

In order to be able to look at schematics etc. during repair and soldering sessions I recommissioned my old monitor months ago and connected it to my main PC that sits on a seperate bench. That solution kind of worked, but going back and forth between different monitors on different benches was a bit impractical. Also, I wanted to connect all my remotely controllable instruments to a separate computer - until now, I used an old ThinkPad for that. ...

Although the Programmable Power Resistor re-uses some components, many design ideas and a good portion of the software of the Programmable Decade Resistor (Programmable Precision Resistor), there were many changes and also some improvements regarding some aspects of the mechanical construction and the code. Rear panel with two 60mm fans, USB connector and Line input Features and specs So now it’s time to present the feature list/specs: ...

The Programmable Power Resistor consists of two large boards: The User Interface and Controller Board and the Relay and Interface Board. Because of the use of relays that isolate the input from the circuits, all circuits can be and therefore are earth-referenced. The only microcontroller, a STM32G441RBT6, is located on the User Interface and Controller Board. It implements a SCPI interface via USB (VCOM), the user interface and the logic to control the relays. All relays, the relay driver circuits, some external and internal interfaces and the AC/DC converter can be found on the **Relay and interface Board **. ...

The HP/Agilent 6632B is a remarkable power supply. There are some similarities with the mobile communication DC source 66309D I “repaired” recently: The 6632B is optimized for a fast transient response and it has a low current range too. But the circuit and its properties differ significantly. One important aspect: Where the 66309D only has a downprogrammer that doesn’t track the current setpoint, the 6632B goes all-in: It’s a two-quadrant power supply - able to source and sink current over the full operating range from 0-20V at 0-5A in CV and CC mode. ...

In the last post we had a look at a simple topology that allows us to switch between a series and a parallel connection of two resistors: Now we’ll nest these structures so that we have four resistors: The interesting part here is that two of the four switch states of the outer structure don’t provide any new resistance values: With S1aS_{1a} open and S1bS_{1b} bypassing the R1bR_{1b} we’re left with R1aR_{1a}. Again, this assumes the R1a=R1bR_{1a} = R_{1b}. If S1aS_{1a} is closed and S1bS_{1b} in the upper position, then the total resistance will be 0, exactly like with only R1aR_{1a}. Here I assume ideal switches. The series and parallel connection of both R1aR_{1a} and R1bR_{1b} alone is worth it though. ...

For the performance checks and calibration of my Agilent 6811B AC Power Source/Analyzer (375VA) I need a 20 Ohm resistor with a ton of power handling capability. The original plan was to mount 8 wire wound 50W resistors on a heat sink and be done with it. Then I thought: Why not reuse all the code I’ve already written for the programmable resistor and build a programmable high power resistor that can complement my DC load for AC applications. ...