EEVblog #568 - Solderless Breadboard Capacitance - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: January 15, 2014, 12:10:12 am
content: What is the actual capacitance of typical breadboard contacts?It's not in the datasheet, so Dave decides to measure it.It is well know that breadboards are not suitable for high frequency work due to the stray capacitance between contacts, but how bad is it really?

author: rolandpenplotter
author_rank: Regular Contributor
timestamp: January 15, 2014, 12:22:54 am
content: First... to tell you that this is not the TV Tx teardownIt is, however, another fine video from my mate Dave - thanks mate

author: JoannaK
author_rank: Frequent Contributor
timestamp: January 15, 2014, 12:59:28 am
content: One thing that can also cause problems with these is the quality of the contacts. Some of those breadboards have quite weak mating points, so there are a lot of resistance variance.

author: AlphZeta
author_rank: Regular Contributor
timestamp: January 15, 2014, 01:02:19 am
content: The inductance of the traces/wires also cannot be ignored especially for higher frequencies. This is another reason why breadboards are only suited for simple circuits well under 1Mhz.

author: EEVblog
author_rank: Unknown
timestamp: January 15, 2014, 01:08:05 am
content: Quote from: wilfred on January 15, 2014, 01:00:50 amIt's one of those "it depends" things.For say TTL level digital stuff you can probably get away with running 10MHz on a breadboard, and I've probably done that high myself in the past and gotten away with it. But something like a 1MHz switchmode controller probably would work very poorly or not at all on breadboard. Even 100KHz is going to cause trouble due to the loop inductances, capacitance, and general dickiness.

author: Zucca
author_rank: Unknown
timestamp: January 15, 2014, 01:18:37 am
content: Dave you forgot to tell the max current you can use on a breadboard. You would have save 1000 of innocent young players from burning their brand new breadboard! I personally never go above 1A since there is no restore button after you melted it.How about to see if the C change with the temperature/current on the contact?And what if you install the breadboard on a metal plate or a plastic one?Nice point anyway....

author: BytesGuy
author_rank: Regular Contributor
timestamp: January 15, 2014, 01:21:13 am
content: Quote from: EEVblog on January 15, 2014, 01:08:05 amI've got a system that runs at 4MHz using TTL stuff on (several) breadboards and it works great, never had a problem

author: Rufus
author_rank: Super Contributor
timestamp: January 15, 2014, 01:52:57 am
content: Quote from: wilfred on January 15, 2014, 01:00:50 am2.5pF at 1MHz is about 63k ohms. If you have a circuit where stray 63k impedances are a problem then 1MHz is too high. A lot of digital circuits wouldn't care about a stray 1k so 60MHz would be practical.

author: adh
author_rank: Contributor
timestamp: January 15, 2014, 01:57:17 am
content: Quote from: EEVblog on January 15, 2014, 01:08:05 amIn my experience, anything TTL that is readily available in DIL packages (say 74F/HCT/HC) is slow enough so stray capacitance of breadboard does not make much of a difference, you get effects of insufficient decoupling (which is not exactly trivial on breadboard) or even problems with correct probing much sooner than anything related to stray capacitance.Probably fastest thing that I have ever built on breadboard was bunch of (relatively trivial) HC series logic running around 60MHz and it essentially worked, althought "general dickiness" was certainly present (with major causes being decoupling and slightly hackish clock oscillator).

author: Odysseus
author_rank: Regular Contributor
timestamp: January 15, 2014, 02:23:15 am
content: I'm curious to know the capacitance between a contact and the ground plane formed by the metal plate that the board and binding posts are mounted on. I've noticed on many breadboards that one binding post is explicitly designed to make electrical contact with the plate. The attached picture is the bottom of a 3M solder-less breadboard.

author: EEVblog
author_rank: Unknown
timestamp: January 15, 2014, 02:31:53 am
content: Quote from: zucca on January 15, 2014, 01:18:37 amIf your contact is heating up enough then I suspect that capacitance is the least of your worries!

author: EEVblog
author_rank: Unknown
timestamp: January 15, 2014, 02:33:13 am
content: Quote from: Odysseus on January 15, 2014, 02:23:15 amThat's a different ball game again. I don't have a metal one to test. Would depend entirely upon how it's stuck down to the plate and the insulating material used.

author: rolandpenplotter
author_rank: Regular Contributor
timestamp: January 15, 2014, 02:50:48 am
content: I took this photo a couple of months ago; I thought it would come in useful sometime:

author: bktemp
author_rank: Super Contributor
timestamp: January 15, 2014, 06:38:35 am
content: In the video Dave said the capacity changes with frequency. Is this really true in the frequency range Dave was talking about (50Hz - 100kHz)? Or is it more the accuracy of the LCR meter that effects the value?

author: cybermaus
author_rank: Frequent Contributor
timestamp: January 15, 2014, 06:58:26 am
content: So, does anyone know the function of the gutter/divider in the middle? They all have it, without fail.the gutter width is set to DIP distance of course, but there is no reason to make a gutter for DIP IC. Some more unused contacts would be OK as well. And sometimes I wish I could span a 5mm (2x2.54 pitch) cap over the gutter witch is not possible.The only reason I can think of a need for a gutter is if you have some component that has a dangly bit under the pins, but I have never seen such a device. Or more imaginative, to drain the magic goo that escapes together with the magic smoke.So, anyknown knows why the gutter is there?

author: thmjpr
author_rank: Regular Contributor
timestamp: January 15, 2014, 07:11:56 am
content: If you are looking for a worst case scenario and add everything up: signal and ground on both sides (2*2pF) + power rail (1pF) + across center gap (1pF). Mine has the metal backing plate as well, which is ~2pF. But it is not connected to the green terminal.Perhaps this is what some people are referring to, as that is getting close to 10pF.Quote from: cybermaus on January 15, 2014, 06:58:26 amEasier to grab under the chip and remove it with your fingers.For extra contacts, you could only add one row due to clearance required. Then your chip is offset from center and it would just look wrong :p

author: ion
author_rank: Regular Contributor
timestamp: January 15, 2014, 11:06:28 am
content: Quote from: zucca on January 15, 2014, 01:18:37 amI've got a breadboard mounted on a metal plate and I measured ~2.5pF between contacts at 100kHz. So I guess the backing material doesn't have much of an effect.

author: popamp
author_rank: Newbie
timestamp: January 15, 2014, 11:46:52 am
content: Nice video Dave!I hear about the capacitance between leads on different packages (i.e. DIP vs SOIC etc.) - any chance of conducting a similar experiment on adjacent leads of different IC packages?

author: ion
author_rank: Regular Contributor
timestamp: January 15, 2014, 11:47:56 am
content: Quote from: EEVblog on January 15, 2014, 02:33:13 amI tested mine: 4 - 4.5pF between the metal backing plate and the contacts, ~ 18pF for the power rails. There's around 1mm of foam between the contacts and the plate (and a layer of paint).

author: KJDS
author_rank: Super Contributor
timestamp: January 15, 2014, 12:01:09 pm
content: Quote from: bktemp on January 15, 2014, 06:38:35 amProbably a bit of both but mostly the meter. Some dielectrics do very funny things at very low frequencies.Quote from: cybermaus on January 15, 2014, 06:58:26 amThat's a plastic moulding issue, the same as you have with metal castings.Keeping the thickness the same all the way through rather than having a thick section makes the moulding process work better, the plastic sets more evenly and prevents longer wait times before it can be removed from the mould and bending issues that would otherwise occur.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: January 15, 2014, 01:01:29 pm
content: Quote from: KJDS on January 15, 2014, 12:01:09 pmI can think of two other reasons that don't have anything to do with the molding.1) To indicate visually that the two sides are not electrically connected. This should be obvious, but it's good to show it visually for first-timer users.2) So you can insert a small screwdriver or other stick-like object to lever out the chip.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 15, 2014, 03:47:15 pm
content: Quote from: cybermaus on January 15, 2014, 06:58:26 amCooling and making sure a hot IC doesn't burn the plastic instantly.

author: w2aew
author_rank: Super Contributor
timestamp: January 15, 2014, 07:00:33 pm
content: Quote from: EEVblog on January 15, 2014, 01:08:05 amYes - definitely one of those "it depends" things. 1MHz is a pretty safe limit. I think I stated a typical limit of a few MHz in my video, but of course "it depends. The biggest factors are things like:1) The fact that it is much more difficult to create good, broadband power supply decoupling due to lack of ground plane.2) The 2-2.5pF capacitance exists between every adjacent node, so you have to consider the effects of this node coupling (not capacitance to ground)3) High impedance nodes will be most dramatically affected.4) Feedback networks can be particularly problematic - especially where the node-node capacitance is magnified by circuit gain, or where node-node capacitance forms a positive feedback path.5) etc...

author: electronics man
author_rank: Frequent Contributor
timestamp: January 15, 2014, 08:55:14 pm
content: If u can't use breadboard for switch old power supplies how do you prototype them first time

author: open loop
author_rank: Regular Contributor
timestamp: January 15, 2014, 09:11:07 pm
content: Quote from: Bored@Work on January 15, 2014, 03:47:15 pmI am going to do a quick check to see if the plastic that has been heated and melted makes any difference to its dielectric properties. My hunch is not at all... Yes I have an abused breadboard from when the TTL chip got wired wrongly and then it got very hot and then melted the breadboard.When I was a youg lad I built the radio in the ladybird book "making a transistor radio" by the Rev George Dobbs. That was on the original wooden breadboard using OC71 transistors, still got the book. Sadly the radio is long gone...

author: w2aew
author_rank: Super Contributor
timestamp: January 15, 2014, 09:31:45 pm
content: Quote from: electronics man on January 15, 2014, 08:55:14 pmHave you seen my video on prototype construction techniques? Several of these techniques could be used to build a prototype of a switch-mode power supply.

author: FrankBuss
author_rank: Unknown
timestamp: January 15, 2014, 09:58:52 pm
content: This could be useful is you want to test different low value capacitors:Looks like it is pretty linear, the wires don't matter much. And I guess it will be pretty stable as well, no microphonic or other effects as known with cheap X7R capacitors, and very temperature stable.

author: tszaboo
author_rank: Super Contributor
timestamp: January 15, 2014, 10:19:23 pm
content: Quote from: electronics man on January 15, 2014, 08:55:14 pmYou dont. The layout is an essential part of an SMPS. If you design one, chances there wont be any through hole parts, and the IC will be one of the leadless DFN or similar package. The only way to prototype it is to run a smaller board containing only the layout. Then you can try multiple parts.But right now I'm only talking about 1-10W POL SMPS

author: KJDS
author_rank: Super Contributor
timestamp: January 15, 2014, 10:31:46 pm
content: Quote from: NANDBlog on January 15, 2014, 10:19:23 pmMost of the little ones have applications boards available from the manufacturers.

author: JoannaK
author_rank: Frequent Contributor
timestamp: January 15, 2014, 11:05:06 pm
content: Quote from: KJDS on January 15, 2014, 10:31:46 pmAnd one can puchase entire prebiuld SMPS module from chinashop at the price of parts or lower..Another option are those factory potted switch modules. I rememeber seeing 78xx plug in replacement switchers with merely few bucks (5?) in singles quantity.

author: JackOfVA
author_rank: Unknown
timestamp: January 15, 2014, 11:17:05 pm
content: For low capacitance prototyping, you might consider the island pad approach using a diamond tipped core drill - it's described at my web site pagehttp://www.cliftonlaboratories.com/Prototyping.htmMeasured capacitance is less than 1 pF and I've built circuits with that up into the 100 MHz range and above.Or the push-in Teflon pin approach - it's illustrated towards the bottom of that page. That yields low C and very high leakage resistance for those circuits where G-ohm leakage is needed.Jack

author: Maxlor
author_rank: Frequent Contributor
timestamp: January 15, 2014, 11:22:46 pm
content: Quote from: EEVblog on January 15, 2014, 01:08:05 am(emphasis mine)I love that expression of yours. I suggest we should make it the official measure of reliability of a given design. The unit we measure would be the Dave of course! And the higher the unit value, the higher the amount of dickiness, so I propose 1 Dave => it works on the first attempt, 10 Daves => it takes 10 attempts to get it working, and so on

author: Zucca
author_rank: Unknown
timestamp: January 16, 2014, 03:23:41 pm
content: Quote from: w2aew on January 15, 2014, 09:31:45 pmAmazing, just thank you. Keep going on I suscribed to your channel.Quote from: FrankBuss on January 15, 2014, 09:58:52 pmNice idea! Why I did not think about that in the past?

author: electronics man
author_rank: Frequent Contributor
timestamp: January 16, 2014, 06:54:56 pm
content: Quote from: cybermaus on January 15, 2014, 06:58:26 amWell I have had to use heat sinks whith large fat legs on them that fits perfectly in that bit I have also have used rotary encoders whith pins in the middle for strength that fits in the bit in the middle so yes it does have a pepose

author: georges80
author_rank: Frequent Contributor
timestamp: January 16, 2014, 07:28:19 pm
content: With the cost of proto PCB places and most 'modern' circuitry being SMT I haven't used one of those solderless breadboard units for well over 20 years and don't own one here in the US. I know there's one back in oz in my parents garage (where all my electronics junk ended up) from my 'youth'.All my prototyping since being here (digital) was wirewrap and that would happily run into the 20MHz range with careful placement of the wire runs (to prevent crosstalk and other nasties).Now everything I do is surface mount and for <$100 I can get a bunch of different protos on one panel in <1 week. Seems totally pointless to not go straight to PCB these days and not have to fight with layout issues which is important in my case since all my designs are uC based and/or typically have reasonably high current switchers.For just daydreaming, it's easier to just throw the circuit up on LT spice to verify that it should be 'close' to working the way you think and then put it on a pcb proto run.I sometimes have little designs that I think would be neat to try out, so I just design them up, do the PCB layout and add it to a panel. Once I have enough on a panel (maybe every month or two) I'll send the panel in to one of the PCB proto places (that doesn't charge a premium for a panelised board) and then I have a bunch of neato little things to build/test for a few weeks. I often put programming adapters for the AVR chips I use on the panel (for the 6 pins ISP header and the mating pogo pins for the PCB layout under test) and also put test adapters (again with pogo pins). This means I can have designs that don't require the 3 x 2 ISP but can have the pins spread all over the board where it makes sense from a routing perspective (most of my boards are relatively small/tight and 2 layer).cheers,george.