Author: Sebastian Harnisch

  • Programmable Decade Resistor: Optimization

    Programmable Decade Resistor: Optimization

    I went into this project with the thought that it will be a rather small one. This certainly influenced some decisions I made along the way. Now that the project had evolved into a much larger thing than initially anticipated it’s reasonable to have another look at possible optimizations, albiet the calibration results were already…

  • Progammable Decade Resistor: Calibration results

    Progammable Decade Resistor: Calibration results

    In one of the previous posts I covered in depth, how I use the term “calibration” in the context of the programmable decade resistor and how the calibration procedure works. Today it’s all about the result. Also, I’d like to mention the first post in which I defined a rather loose accuracy goal of \(\ll\pm…

  • Programmable Decade Resistor: Warm-up curve

    Programmable Decade Resistor: Warm-up curve

    Generally, test and measurement equipment needs a certain period of warm-up time to provide low drift. That is also true for the programmable decade. I’m especially interested in the warm-up time with all relays off as well as with many relays on. I chose a value of \(100\text{ k}\Omega\) for the second test. (For simplicity…

  • Programmable Decade Resistor: Final Product

    Programmable Decade Resistor: Final Product

    In this post I’ll show a few pictures of the programmable decade resistor in its enclosure.

  • Programmable Decade Resistor: Mainboard

    Programmable Decade Resistor: Mainboard

    The mainboard features the main controller paired with an EEPROM, the resistor decades (precision resistors, signal relays) including two temperature sensors, relay drivers and signal conditioning for the two external digital inputs. Main controller The main controller is a STM32G441KBT6 microcontroller (170MHz Cortex M4, 128kB Flash, 32kB RAM). The microcontroller features a USB 2.0 device…

  • Breakout box for Agilent 6611B AC Power Source

    Breakout box for Agilent 6611B AC Power Source

    I got my Agilent 6611B AC power source/analyzer a few weeks back, but hadn’t used it as much as I wanted. The reason was simple: The connections are made with rear mounted screw terminals – hence it was just a bit inconvenient to interface with products and circuits. The solution was really simple: A Hammond…

  • Programmable Decade Resistor: System Design

    Programmable Decade Resistor: System Design

    The block diagram provides an overview of the different circuit groups of each functional block, their internal connections and external interfaces. The Programmable Decade Resistor consists of three main functional blocks: The power supply board uses an off-the-shelve AC/DC converter to provide a +15V rail. The +15V rail powers the relays on the mainboard as…

  • Programmable Decade Resistor: Switching (3)

    Programmable Decade Resistor: Switching (3)

    Now that we have a calibrated programmable resistance decade, we can try to make the programmable decade resistor more accuracte – for higher resistance values. Actually, the idea behind that is trivial. I’d like to start with an example in which we set a resistance value of \(R_{set} = 100.000\text{ k}\Omega\). (Let’s not worry about…

  • Displaying graphics and text on an oscilloscope screen

    Displaying graphics and text on an oscilloscope screen

    While playing with an old Hameg HM504 and the Tektronix 465B oscilloscope that I repaired recently, I thought that I should do yet another mandatory tinker project: Using a microcontroller to write text on an oscilloscope screen via the XYZ-mode. And so I designed a small USB powered board around the STM32G441KBT6 which seems to…

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