Hi The Humble Breadboard. Yes, you've no doubt got one in your kit and you've no doubt used it before. It is one of the most, uh, popular tools for quick circuit prototyping, and well, for good reason because you can just plug components in, there's no soldering, you can move things around, and you can generally have a play with stuff just to see if something's going to work before you dedicate it to a PCB And it's good for experimentation. but it has, uh, a couple of limitations.

The first one, of course, is that it's not permanent. You know things can. You can get Dicky contacts and all sorts of stuff like that, which we won't go into. But the second is that the breadboard.

As you should know if you don't well, you will now that it's not designed for high frequency, uh stuff, because you know we've got wires hanging all over the place. It's not good. They're all acting as antennas big uh Loops of things which isn't good for switching stuff. For example, you wouldn't want to build a switch mode power supply on here.

for example, it's not going to work that well and uh, you'll see in it as you saw in a previous uh video where I was playing around with this um Precision constant current circuit. Yeah, it's not that great on the breadboard because of all the inter contct capacitance on here. it's you know it's not very good at all, but hey, if you can get something working on the breadboard then that gives you good confidence that it's going to work on a proper PCB When you actually lay the thing out properly, you do nice tight ground loops and power loops and keep everything nice and short and tidy and stuff like that, and you don't have all that stray capacitance between the contacts. now.

Um, you know the rule of thumb in the industry is that sort of, you don't do anything more than like a megahertz on the breadboard or and the inter contct capacitance. Well, I've always taken this normally about 10 puff. you know, 10 paa farads. something like that of that order, but what exactly is it now? I've looked at a few data sheets for these things and well I haven't been able to find an inter contct capacitance value on here.

and well, some figures that are floating around out there um, not actually in the data sheets are anywhere from 2 to 25 picofarads per contact strip and well I don't know what is it I mean that's an order of magnitude difference. Is it two paa farads or is it 20 paa farad? but what is it? Well I decided let's actually measure it. so I've got some breadboards here, a few different uh types, and I've got our LCR meter. so there's nothing better than actually getting real empirical data on this thing cuz I I did a quick Google I Couldn't really find anything out there of anyone who's actually done any real measurements on this thing.

Just is wide. You know, wide. open. Ball Park figure of 2 to 25 paa fets.

So I've got my agilant U7 33c LCR meter here and well, you know, down at 120 htz, it's only got uh .1 paa farads resolution there. But if we go up in frequency, which is what we're going to have to do on this breadboard because the capacitance will change with frequency. Of course it's not going to be fixed. but this puppy, if we go up in frequency 1 khz Bingo we get an extra digit.

we're down to uh 10 uh, fto farads there? Awesome. And there we go. 10 khz. We're now at look at this one.

fto farad resolution awesome but we this one actually goes up to 100 khz as well. and we, but we don't get an extra digit on there. but that's fantastic. so we'll be able to probe that after we, uh, null out the residual reading of uh, the meter and the leads here.

we can null that out. We'll be able to fairly accurately, or you know, good enough measure the capacitance of these various different breadboards we got here. Now if you've never seen inside a breadboard like this, well, you should. You should take the back off and uh, have a look at the actual strips.

They go in columns down here like this and if you flip it over, you can see the metal contacts down in there like that and those little Spring Bar contacts and because they're long like that, they're well, what are they? They're like the plates of a capacitor between any two wires or any two contacts. You're always going to get some capacitance and there's the dialectric material as well. Usually these things are like Phosphor bronze contacts, but some of them can be silver plated as well on your high quality breadboards. and well, you know, and the backing also will have an effect on that.

uh, capacitance. Well, this has just got a spongy backing on it. some I Think this one down in here I Haven't taken it out for a while, but I don't think there's any backing on at all. it's just the hard plastic, uh backing.

There's no sponge on the bottom of that one. So first up, we'll have a look at uh, my main breadboard. I got a few of these K and H brand. It's a decent Uh brand name model RH 32 standard uh tie Point configuration and we'll just measure the vertical uh between two vertical columns down there.

just in a random location shouldn't really matter. all right. So we're at 100 khz here to give us the greatest resolution and to operate at the highest Uh frequency possible. and I haven't actually plugged them in yet I've just got them sort of rest in on there.

so because when you sort of you know touch these leads, it's going to. especially at this sort of resolution, it's going to, change around a bit. like if I put my fingers on there. Of course it's going to go up because of the capacitance of my fingers, but we should be able to null that out.

So I've got 4.6 27 pea farads and that's reasonably repeatable if I you know, dick around with that. hey, you know, gez you fart halfway across the room and this thing's going to change at the moment when we're down at one fto far. But anyway, all right, so let's null that out and see what we get. That's not too bad.

You know that's not too bad. I Mean we can dick around there, but we won't bother. So let's stick that in the breadboard. Look at that two side by side contacts.

it's only 2.4 Paa farads. Look at that. So much for 20 or 10. And just to double check that, let's just remove that again and check the repeatability.

Yeah, you know it's a little bit. it's you know. I Don't have these leads exactly right, but that's going to be near enough. We're in the order of Two paarat.

And if we measure Elsewhere on the board, there we go. 2 and 1/2 right over on the edge. Over here 2 and 1 half so it looks like it's pretty Dar repeatable. And let's go for one of these power strips down here.

I've actually got them connected. uh, like this so that usually they're split in the middle like that so only those along Ong there are connected and those along there and it actually shows you that uh, visually on there. Just For kicks, let's have a look at the uh Power bus. Sometimes it can be a real pain plugging these Square pins in, but there you go, we're over.

look at that, can't handle it. so we're well over now. Let's uh, put that back on our Auto Range There you go. 20 25 paarat or thereabouts for the power bus.

So maybe that's what they're talking about when they talk about that range from 2 to 25 picofarads. But really, all you can. you don't really care about the power. uh, strips down here usually because you're using them for power, so it's not a huge issue.

But uh, you really? the one you got to care about is the inter contact capacit down there. No hang on I haven't Ned that out. So because I changed ranges, it didn't keep the null. So let's null that out and we should find it's around about there we go: 20.

One odd peak of farads for the Power bus. and if you're curious to know what, they are directly opposite over the inner divider in there, well, it's almost unmeasurable. Really? I Mean we're down in the noise of our null? Really, it's you know, it's just not as you'd expect because they're not physically close together and because there's a big chunk of dialectric taken out. So let's null that out.

So I've done this a few times and I have sort of got a repeatable result around. Let's take it as about 0.5 peaka farads there? uh, across the dividing strip on this particular breadboard. And the other thing I Want to check is: does it change if I plug in a fairly large uh, leaded component in there like that? Does it force it open? No. 2.7 There we go.

Don't touch it. but of course, you know, hanging in the air it's going to disturb it a little bit, but generally, no forcing those pins in. You'd expect it because technically they're a bit closer so you'd expect it to increase in capacitance and that's kind of sort of what you see. but it's not really a big deal now.

this little, uh, yellow breadboard, just a one hung low brand I have no idea what it is and uh, but I don't expect any different and no, it's practically the same. And that's what you expect to get because it's based on the physical dimensions and all these board's physical dimensions are basically the same and the diametric constant of the material in there probably isn't going to change a huge amount anyway. I wouldn't expect an order of magnitude difference. So there you go.

it is. Round about that same figure of two puff, two Paa farads, and that one across the Uh dividing strip in the middle, even lower than the other one. Really, it's quite down in the noise and this one across the dividing strip in the middle. even lower than the K&h one.

You know, 2 puff. And we got another generic brand breadboard here. no idea what brand it is. once again, two puff and the power strip on this one.

once again, 20 That same figure of round about 20 puff and one thing I forgot on the other one. Curious to know between the power strip and one of the Uh columns in there we're talking. You know, just over one puff and this uh, pick development board from Gtronic H.net I Don't know the brand of the actual breadboard in here, don't know where he sources it from. but there you go.

Once again, that two puff figure. You can take that to the bank. One thing I haven't done yet. What is the capacitance between um, two contacts that are separated by one unused column? And of course you'd expect it to have.

And yep it does. And yep, it's the same on that one and on that one as well. So there you go. And if if you're curious to know the capacitance at different frequencies, well, at 100 HZ down here, you know half a puff, you know it's barely even measurable down in the noise.

And at 1 khz there we're looking at just over two puff and 10 khz. As you'd expect, it increases slightly again. 2.25 So there you go. I Think that's fairly definitive I mean I've tested uh, four different types of breadboards and they're all identical.

Two Pea Farads capacitance between the individual contacts and you know, pretty negligible when you, uh, jump over, well, go from the power strip to one of the columns, or when you jump across the columns like that. But there you go. you can take that figure to the bank and you can plug that into your Uh simulations or something to see why your breadboard is oscillating. Nothing can beat empirical measured data like that.

I Like it, you know, measure your own breadboard and see what you get. but I reckon you'd be hard pressed. unless the dialectric material material was grossly different. uh, to all of the four different ones here.

then you should get that same figure because the capacitance is based on the physical dimensions and all these bread. Wards As I said, they're going to be pretty identical in that respect. So remember that figure two par per contact. She'll be right.

No worries. So I hope you enjoyed that quick little empirical uh video to actually measure this and if you want to discuss it, jump on over to the Eev blog. Forum Catch you next time and.