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I have this old digital caliper that is rarely used, because the battery is always empty. The issue with these calipers is that they don't have any on-off switch, so they are constantly draining the battery. Basically they only switch off the display. I don't know whether newer calipers also suffer from this problem. It's a shame, because this is a good old caliper. Newer ones look and feel like they are made cheaper. I've seen people on the Internet adding various kinds of switches to their calipers, even external batteries(!), but I've not seen a good solution. The issue has been finding a small enough switch that doesn't interfere with the usage of the caliper. I was lucky with this one, because I found a switch that was a perfect fit without any modification to the caliper. Here is my solution: I used a small DIP switch: DIP switch dimensions are 10 mm x 6.5 mm x 5.5 mm (length x width x height).  On this caliper, there is a small lid on the top side above t...

    This is a DIY capacitor reference box that can be used to verify and compare multimeters. It's not a metrology grade reference, but has capacitors with better tolerances than what is typically available in electronic circuits. It's still relatively cheap. For better results, a calibrated instrument should be used to check capacitor values. The reference box contains capacitors in the range from 10 pF to 10 mF.  It should be said from the beginning, that capacitances below 100 pF is hard to use in a box like this, due to stray capacitances in wires, terminals and the box itself. This is discussed later below. Capacitor types There are many different types of capacitors with different dielectric and specifications. Not all of them have a stable capacitance with regards to temperature, age, voltage, DC bias voltage and other factors. The most stable ones are in general film capacitors, where polystyrene and polypropylene dielectric materials are considered best. Of small...

Building a 1 W, 0.5 % decade resistance The seven decade programmable resistor - my variant. Gerry Sweeney designed and built a really neat little SMD decade resistance board a few years ago. He still offers it for sale, already assembled, check it out! You can find it here: https://gerrysweeney.com/seven-decade-programmable-resistor-a-low-cost-solution/ Screenshot from Gerry Sweeney's site. Gerry Sweeney's design is cheap, simple and uses 1 % and 0.5 W resistors in the 1210 size (metric: 3225). Why build my own? I decided to build a similar board, but to use at least 0.5 % tolerance, better temperature coefficient and higher power resistors. This was more of an exercise to see what kind of SMD resistors are available and if it is possible to design it for higher power output and better tolerance at the same time. The answer is that it is, but it comes at a cost.  What kind of resistors? I tried to use 1206 size (metric: 3216) resistors where possible. They are a bit smaller an...