Products > Test Equipment
Capacitance substitution boxes
kripton2035:
another diy approach : http://kripton2035.free.fr/LabTools/lbt-capacitordec.html
watchmaker:
I bought two substitution boxes. One with the switches recommended by themadhippy and the other a less expensive type off Temu.
Both have small footprints and are accurate to 10% at the terminals as measured with my ST42. Not sure the exact value much matters as you need to include the capacitance of your hookup wire as pointed out by Tgzzz. In both, the steps are consistent. I would simply measure the total capacitance from the end of the hookup wire and find a cap to match after I dialed in a "perfect" capacitance.
The Temu s about 1/6 th the price of the eBay one. But I wonder about the Dip switches. As they fail I would replace with headers and shorting blocks.
https://www.temu.com/1nf-step-4---programmable-capacitor-board-polypropylene-film-capacitor-dc100v-ac70v-g-601099646299921.html?
The eBay one is certainly more expensive https://www.ebay.com/itm/323759946271 . But it is easier to use, and I would expect the switches to hold up. The seller does take offers.
However, these are not like scopes or meters that get used every day. SO switch robustness may not be an issue. And for $10 the Temu is a good deal.
Both of these are a better value than the used Heathkit/Elenco/Eico boxes you find on eBay.
tggzzz:
--- Quote from: watchmaker on September 20, 2024, 02:17:31 pm ---Not sure the exact value much matters as you need to include the capacitance of your hookup wire as pointed out by Tgzzz.
--- End quote ---
Whether or not the exact value is important depends on what you do after you have finished twiddling the knobs :)
Depending on frequency, wire inductance is more likely to be an issue. Of course capacitors also have inductance, some more than others. There's no substitute for understanding :)
Have fun, realise the limitations of whatever equipment you are using.
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