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Is there an equation I can use to calculate:

  1. the actual capacitance between two PCB tracks close together and
  2. the actual capacitance between two adjacent holes of a breadboard

I believe such capacitance is called stray capacitance but I'm not 100% sure.

The reason why I ask is because I make super-regenerative receivers and the results are different when I transfer the circuit to PCB from a breadboard, most notably capacitance values, and I verify this because the reception frequency (station) is different even though I haven't change any values of any components.

The rest of the parts that form the circuit in both cases are exactly the same including the wall wart 5VDC power supply.

I also would like equations in order to make successful tests on the breadboard, so then I don't have to waste solder, or PCB material over failed attempts, and yes I removed and re-soldered components in the past which can be a pain so I want to avoid that route.

Any ideas on how to calculate the capacitance?

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  • \$\begingroup\$ forget "calculate". Measure. I recall measuring a breadboard adjacent-row capacitance of about 5pf. Don't forget there are usually two adjacent rows. Regens are so critical in their oscillating feedback path layout, that the usual method is "build-and-tweak". EXPECT those differences between breadboard & PCB. \$\endgroup\$ – glen_geek Oct 27 '16 at 17:36
  • \$\begingroup\$ measured on EEVblog \$\endgroup\$ – CL. Oct 27 '16 at 17:57
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so then I don't have to waste solder, or PCB material over failed attempts, and yes I removed and re-soldered components in the past which can be a pain

  1. Solder is cheap.

  2. Design your PCB using larger parts than are strictly necessary. 0805 parts are much easier to rework than 0402.

  3. Design your footprints with slightly more fillet area than the minimum. If the pad extends a bit beyond the end of the part, it will be much easier to rework.

  4. Design your PCB with extra part locations for trimming. This lets you adjust effective part values in smaller steps than the standard values allow.

Now you don't need to muck around with crummy breadboards.

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There is a fantastic, free piece of software called Saturn PCB Design Toolkit that will help you out with this and pretty much any other calculation you need to do when creating PCBs.

I can't remember off the top of my head whether it offers a calculator for capacitance between two tracks (with varying voltages) though, but it offers pretty much anything related to microstrips over a plane or a track with regards to surrounding ground and a lot of other useful stuff.

Link here

With regards to your question though, I would assume you would be more interested in capacitance related to ground rather than between two tracks or two via's? This is something Saturn definitely can help you with.

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