A few days ago I got my hands on a faulty Agilent 66309D Mobile Communication DC Source. To be honest, I don’t think I need it, but it was pretty cheap and I was looking for something to either repair or potentially salvage the case of. The Mobile Communication DC Source is a specialized power supply. It not only has an improved transient response, but also a few other features not found on standard power supplies (e. g. E363x, E364x). The list for the Agilent 66309D includes (not necessarily exhaustive): ...

I didn’t really think about the BOM cost of my programmable decade resistor until I was asked. Then I also wanted to know. It is fairly difficult to put a number to what I paid, since I had a lot of components left from other projects that I could use. This includes not only cheap chip resistors and MLCCs, but also connectors etc. Normally I order from both mouser and digikey, but for some of the industry-standard components, connectors etc I use local distributors. This is why I’ll only give a very rough estimate for the per unit costs including taxes (not including any shipping costs). For some of the parts like the PCBs there is a minimum order quantity that will increase the cost in most DIY scenarios. ...

For some time it became more and more difficult to get a click out of the mouse wheel switch of my old Logitech M310 mouse - inconvenient in programs like KiCAD. I also have a newer and “better” M705 mouse, however, using this one seemed to increase fatigue compared with the old M310. The mouse wheel switch SW3 (center) is one of the cheap through-hole tactile switches used everywhere - and sure enough, I didn’t even have to order a replacement. After a tiny bit of disassembly, desoldering, replacing old switch with a new 10 cent one, soldering and re-assembly it works perfectly again. Certainly cheaper and more fun than buying a new 30 to 40 EUR mouse. Why didn’t I do that sooner? ...

I was asked a few times how I did the front and rear panels, so this is what I’d like to talk about in this blog. There are different ways to achieve a similar result. For me, the easiest and most cost-effective solution was to just design another PCB - I know how KiCAD works and it does everything I need it to do. The basics Depending on the actual use case you can use a regular FR-4 board. For this project, however, I chose an aluminum PCB. Those only have one copper layer and the prototyping service might specify different process parameters for slot width etc. But other than that it is very similar to designing a regular PCB. ...

After being asked about some aspects of the mechanical design and components used a few times, I’d like to address those questions. I have to admit that I’m neither very good at mechanical design, nor do I have a 3d printeror a workshop where I can do metal work myself. That being said, I was still able to design a reasonably professional looking device and bring it to life with the help of modern prototyping services. ...

Currently, the unit’s setpoint accuracy isn’t all that great (readback resolution is limited as well, but shows the offset): Regardless of the range it has an offset of about +20 mA. Sure, for a unit capable of 60 A that seems reasonable, and well within its specs of ±0.1% ±75 mA. But since I’ll use it in the low range (6A) most of the time and likely often even well below 1A that doesn’t seem too great, does it? ...

I recently got my hands on a HP 6060B System DC Electronic Load (later also sold as Agilent 6060B). My unit has option 020 installed: Comically large binding posts also on the front panel. This option certainly is not unheard of, but not too common either. Retrofitting is possible, but can be quite some work. Huge binding post also on the front panel thanks to option 020 ...

After the modification described in the previous post I let the the “adjustment”/calibration procedure run again. Five days later I repeated the calibration (not the adjustment). As before, all measurements are performed with an Agilent 34401A 6.5 digit multimeter. Accuracy of the resistance First up is a diagram that shows the absolute value of the deviation of the measurement value from the setpoint. The tested values are grouped as follows: ...

A bit over a decade ago I built a word clock - one of my first microcontroller projects. The project was fairly expensive: It uses a large stainless steel front panel (ca. 39cm x 39cm, laser cut) and a similar sized PCB. Over the years I had to resolder one or two of the RGB LEDs and replace a failed one, but other than that it’s still working as intended. ...

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 pretty satifactory. The problem with the contact resistances From the start it was clear that the relays’ contact resistances will reduce the accuracy of the programmable decade resistor, especially in the lower two decades. (When using 0.1% resistors, for the third decade and up, the tolerance of the resistors is of the same or a higher magnitude than the contact resistance of the relays. So it’s much less important or even pointless to compensate for the contact resistance in those instances. This is especially true for the highest two decades where the algorithm described in a previous post can effectively eliminate the deviation by adjusting the “hardware setpoint” according to calibration values.) ...