Electronics blog
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Programmable Decade Resistor: Switching (1)
In the previous posts we discussed the topology selection as well as the power handling capabilities of the decade resistor. Now it’s time to have a look at different aspects of switching. Today it’s all about the effect of the contact resistance of the relays, which impacts the performance of the decade resistor, not only,…
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A Nice Case for Projects
For projects like the programmable resistor I was looking for a case, preferably made of aluminum and 19″ compatible. In order to save some space on the desk I hoped to find one with a width of 42HP (i. e. half width). What I found was a beautiful case made by ELMA (2 RU, 42HP),…
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SCPI Capable Thermometer
For a long time I wanted to build an SCPI capable thermometer to keep track of the ambient temperature in my small lab. The list of requirements was fairly short: Design After researching temperature sensors I chose a Texas Instruments TMP117M temperature sensor with quite impressive specs. With an accuracy of ±0.1°C (max.) between 25°C…
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Programmable Decade Resistor: Power Rating (2)
In the last post we discussed how to calculate the power rating of the programmable decade resistor. We assumed that the decade resistor is made of resistors with the same power rating – in reality this might not be the case. Also, it might be a good thing to derate the resistors a bit. So…
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Programmable Decade Resistor: Power Rating (1)
In the last post we worked on some implementation details to consolidate the bill of material while improving the power rating of the decade resistor. However, we didn’t actually analyze the design regarding power dissipation. So let’s get some definitions out of the way (goto Conclusion for tldr): \(n\) Decade \(n\) providing resistance values \(0\Omega\),…
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HP Instrument feet
Many older HP/Agilent instrument share a similar feet design. There are at least two different types though: One with a metal part to prop up the instrument and one without it that can be used on all four corners. The feet can be detached from the instrument, e. g. for use in 19″ racks. This…
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Brymen BM789: Not a Review
Almost two years ago I bought a Brymen BM789 Multimeter. And there is a lot to like about it. It has great specs, is feature-packed, feels high-quality and yet it’s well priced. But there are also some mostly minor aspects I don’t like: My main issue though and this is not limited to Brymen (hello…
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Agilent 34401A repair
The other day I noticed an issue with one of my Agilent 34401A’s: I measured a constant DC voltage and after a few minutes the measured value would start dropping and become unstable. Then I got curious and checked the two-wire resistance mode. Same story, maybe worse. A word of caution: High voltages found inside…
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Programmable Decade Resistor: Topology (2)
In the last post we selected a resistor network and switch topology that suits the needs of this programmable resistor. Now we will apply simple optimizations that allow an effective and cost-efficient implementation. Optimizing the bill of material In order to reduce the number of different components the single \(1 \Omega\) is replaced by two parallel \(2…