Voltage Drop at Breadboard - Page 1
Forum section: electronics / beginners

author: anbudroid
author_rank: Newbie
timestamp: March 09, 2019, 06:53:33 am
content: Hello Everyone ..I Have a Chinese Bench power supply set its voltage to 7.5V send it Directly to DC-DC step Down Module Mounted in a breadboard. The output voltage of 5.07 from DC-DC Connected to Arduino nano and 1602 LCD. but after connection the voltage drop to 4.68. I remove the bread board and jumper cable and solder everything together then the voltage at arduiono 5V input is 5.04 . what cause this problem? I swap my old breadboard with new one but problem not solved .Am new to this forum. Searching internet for 3 days about voltage drop in breadboard and didn't find any result regarding this topic . so I thought this only happen to me. this is my second college project of my brother I plan to help him in his electronic side. so I bought some breadboards , jumper cables and few op amps to play around little bit before we start . we both are not have much knowledge in electronics.

author: mycroft
author_rank: Regular Contributor
timestamp: March 09, 2019, 10:35:31 am
content: Many DC/DC converters requires a minimum load to satisfy the output voltage specification. Seehttps://power.murata.com/datasheet?/data/power/ncl/kdc_cre1.pdf. The no load voltage can be much (>20%) higher.

author: tggzzz
author_rank: Super Contributor
timestamp: March 09, 2019, 11:06:02 am
content: The problem is that you are using solderless breadboards. Inevitably you will spend more time debugging the breadboard than the circuit, due tovariable and varyingstray resistance, capacitance and inductance.It is much easier to copy the masters, and use manhattan techniques or rat's nest techniques.

author: Ian.M
author_rank: Super Contributor
timestamp: March 09, 2019, 11:08:45 am
content: Anyone working with Arduinos with female headers, or solderless breadboards etc. nneeds to be aware there's a lot of cheap and nasty flexible jumper cables with Dupont pin ends out there that are defective.Common defects are: the stranded wire used is far too thin; it isn't even copper wire; the ends aren't properly crimped; the wire has broken internally. In all cases the resistance of the jumper will be excessive and if you draw a significant current through it you'll get a large voltage drop.Check the jumpers resistance before use after straightening it out and tugging gently on its ends to see if the crimps are loose or the wire's broken. If it feels springy when you try to straighten it, or stretchy when you tug the ends, breaks, or the resistance reads more than a fraction of an ohm over the reading you get with the test probes touching each other, discard that jumper.If you have more than one that are high resistance you can investigate further by stripping the wire and observing if its too thin, or if the wire is attracted to a magnet (copper coated steel), or fails the flame test (copper coated aluminum).N.B the flame needs to be yellow as show, not a fully oxygenated blue blowtorch style flame as that can (just) reach the melting point of copper.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 09, 2019, 11:09:35 am
content: How much current is your LCD pulling out of the power supply?4- line displays may go upto 100mA, maybe 200mA.That would be:U = I * R =>R = U / I =>R = 200mV / 200mA = 1 Ohm.This seems excessive.The cheap Dupont wires from China often have a relaltively high resitance (usable for signal wires, but be carefull for power supplies)Another possibility is your electronics boards drawing high current peaks, which result in short voltage dips, which get averaged by your DMM.You can try distributing a few ceramic 100nF caps over the horizontal breadboard power distribution bar and add a fairly large buffer elco (100uF or so) to the right of the breadboard.

author: Audioguru
author_rank: Super Contributor
timestamp: March 10, 2019, 01:58:36 am
content: The contacts that grab wires on a Cheap Chinese solderless breadboard are dirty or corroded and make poor connections.

author: IanB
author_rank: Super Contributor
timestamp: March 10, 2019, 02:08:47 am
content: Quote from: anbudroid on March 09, 2019, 06:53:33 amAs others have said, the problem is excessive resistance in the jumper wires, the wire/breadboard contacts, or the breadboard itself (or a combination of all three).But is there any reason you don't set the bench power supply to 5 V and use it directly to power the modules?

author: IanB
author_rank: Super Contributor
timestamp: March 10, 2019, 02:15:17 am
content: Quote from: tggzzz on March 09, 2019, 11:06:02 amWow, pessimist much?People have built whole working microcomputers on solderless breadboards with hundreds of jumpers. For simple, basic circuits breadboards are not that terrible.

author: anbudroid
author_rank: Newbie
timestamp: March 10, 2019, 03:45:10 am
content: am using single stead cable . but from scrap. I try with new one sir. I realise pre made jumper cable's are too thin and failed to conduct more current. is there any link for good quality cable ? ali express links is better for me to get

author: anbudroid
author_rank: Newbie
timestamp: March 10, 2019, 03:47:07 am
content: I tested without DC-DC too sir. I use DC DC because my brothers project interface with 12V system.

author: anbudroid
author_rank: Newbie
timestamp: March 10, 2019, 03:48:42 am
content: Total Current Consumed by the LCD and Arduino Board is just 120mA . am not using prebuild breadboard cables I know they were not quality products so that I use single stead 22AWG Cable for BreadBoard

author: Jwillis
author_rank: Super Contributor
timestamp: March 10, 2019, 04:01:43 am
content: Using those cheap bread boards is fine.They work just as well as the expensive ones. Check that you have enough supplied current .

author: metrologist
author_rank: Super Contributor
timestamp: March 10, 2019, 04:30:49 am
content: I have ten breadboards and I've been using a spool of old school solid copper 4 conductor phone line to make jumpers. It is a little thin but solid copper and cheap.Some of Arduino clone regulators are weak, if you are using that. I get low voltage.

author: anbudroid
author_rank: Newbie
timestamp: March 10, 2019, 05:49:01 am
content: Quote from: metrologist on March 10, 2019, 04:30:49 amYes Sir. My bench power supply current is 1A . But the circuit Just need below 200mA . and at this point total current consumption of the circuit including LCD is 150mA from Bench PSU.

author: anbudroid
author_rank: Newbie
timestamp: March 10, 2019, 05:50:25 am
content: Quote from: metrologist on March 10, 2019, 04:30:49 amAm not trust Arduino's inbuilt passive regulator. that's why am using separate DC-DC Buck Convertor. I tried with phone line cable too just now.alternatively give 12v to bread board and connect a load to other half side of the breadboard voltage drop is 400mV . so nominal resistance of my bread board accourding to ohms law is 0.2ohms. is this correct ? total current by the load is 500mA

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 10:30:28 am
content: Quote from: IanB on March 10, 2019, 02:15:17 amLong experience, both mine and others. That probably means there's more realism than pessimism. Start by considering this thread, and look closely at the useful pictures the OP supplied!Quote...and then somebody sneezed.Youcango over the Alps/Rockies/Himalaya on a push bike - many people have done all of those. But expect to have to spend a lot of time fixing problems with the bike

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 10:34:25 am
content: Quote from: anbudroid on March 10, 2019, 03:45:10 amEven if you have good wires, you still have the problem of getting a goodand reliablecontact.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 10:35:42 am
content: Quote from: Jwillis on March 10, 2019, 04:01:43 amI disagree with the first sentence, but agree with the second.

author: windsmurf
author_rank: Frequent Contributor
timestamp: March 10, 2019, 10:47:22 am
content: You might try multiple jumper cables for each connection to reduce resistance, if poor cable is the issue.

author: tooki
author_rank: Super Contributor
timestamp: March 10, 2019, 02:02:40 pm
content: Quote from: Jwillis on March 10, 2019, 04:01:43 amI'm the opposite of tggzzz: I disagree with both sentences.Some cheap breadboards are fine, but others areawful. I've got some cheap ones that have several ohms contact resistance, which absolutely makes itself known in many circuits. Better cheap ones are sub-ohm, and top-quality ones just in the mOhms.Given the issue of voltage drop here, I'd suspect that it's a cheap breadboard and contact resistance is adding up.

author: Audioguru
author_rank: Super Contributor
timestamp: March 10, 2019, 04:03:20 pm
content: I gave up using solderless breadboards many years ago. Then I used stripboard with everything soldered and had no problems. The stripboards were neat and tidy with no messy tangled pile of wires all over the place and the strips of copper cut to length and a few short jumper wires formed the wiring of a pcb. If a part needed to be replaced then my solder sucker easily removed it. Most of my circuit designs were for audio or communications and were custom so only one or two needed to be made. My stripboards looked so neat and tidy that my prototype was usually sold as the finished product. Some were very complicated with many parts.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 04:25:21 pm
content: Quote from: tooki on March 10, 2019, 02:02:40 pmJust soMy agreement with the second sentence was a subtle dig at breadboards because of what Iomittedto say. My longtime experience is thatbothcheapandexpensive solderless breadboards are an unnecessary and unacceptable waste of time!

author: tooki
author_rank: Super Contributor
timestamp: March 10, 2019, 05:02:50 pm
content: Breadboards may be categorically unsuited to some types of circuits, but they're of incredible value to beginners especially. There's a TON of value in being able to quickly lash together a circuit and play around. It takes far longer to solder something together, and making changes are even harder still. I think you guys forget that breadboards are, above anything else, a learning tool — you guys are experienced and knowledgeable, but for those of us still figuring things out, breadboards are incredibly useful.Just don't buy cheap!

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 06:19:14 pm
content: Quote from: tooki on March 10, 2019, 05:02:50 pmTrue, they are a good way to learn about unexpected extra "components", and how to debug imperfect implementations (cf designs).

author: Zero999
author_rank: Super Contributor
timestamp: March 10, 2019, 06:20:51 pm
content: I'm not convinced the breadboard is this issue in this case. Whenever anyone mentions breadboard, there's always this discussion which is valid, but is also a distraction.I'm more suspicions of the DC:DC converter.anbudroid,Did you measure the voltage directly at the DC:DC converter's input and output terminals on the board?

author: IanB
author_rank: Super Contributor
timestamp: March 10, 2019, 07:03:40 pm
content: Quote from: Zero999 on March 10, 2019, 06:20:51 pmDon't the pictures attached to the first post show these measurements?

author: rdl
author_rank: Super Contributor
timestamp: March 10, 2019, 08:42:13 pm
content: Don't use the rails on the breadboard. Run long wires for power directly to and from the DC-DC converter to the devices being powered. Connect them in the closest hole(s) to the part's power pins. Maybe even in the same hole if it's not too tight. If that fixes the problem then you might have a bad breadboard or the existing connections are bad. If it doesn't fix the problem, then something else must be wrong.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2019, 09:10:13 pm
content: Isn't debugging solderless breadboards so much ... fun. And such a good way to learn electronics too.

author: Zero999
author_rank: Super Contributor
timestamp: March 10, 2019, 10:45:32 pm
content: Quote from: IanB on March 10, 2019, 07:03:40 pmYes, you're right, I didn't look.

author: sleemanj
author_rank: Super Contributor
timestamp: March 11, 2019, 12:12:03 am
content: There is no magic, it's resistance, the question is where is the resistance. If we look at your pictures between the DC/DC and the arduino are MANY connections into the breadboard, the DC/DC into two holes, then a pair of jumper wires from there to the rail (4 connections), then a pair of jumper across the rail break (another 4 connections), then another pair of jumpers from the rail down to the nano (another 4 connections), then the nano's connection down itself, another 2, that is 16 connections (8 + and 8 -) to between the DC/DC and the nano, I am not surprised to see even a couple of ohms lost there just in connections.Chuck a decent sized cap across each device's power connection on the breadboard and that will help matters (if they need helping, if everything works, why worry).

author: windsmurf
author_rank: Frequent Contributor
timestamp: March 11, 2019, 12:42:45 am
content: Quote from: tooki on March 10, 2019, 05:02:50 pmWhat is a good breadboard kit to buy? Thx.

author: rdl
author_rank: Super Contributor
timestamp: March 11, 2019, 01:25:15 am
content: Quote from: windsmurf on March 11, 2019, 12:42:45 amhttps://www.eevblog.com/forum/chat/3m-breadboards-for-cheap/Note that the first post also has links to three other threads about breadboards.

author: Peabody
author_rank: Super Contributor
timestamp: March 11, 2019, 04:58:47 am
content: Julian Ilett has a recent Youtube video that appears to show a source of good, cheap breadboards:The Ebay.com link for this item appears to be this:https://www.ebay.com/itm/253085438896

author: tggzzz
author_rank: Super Contributor
timestamp: March 11, 2019, 11:44:18 am
content: Quote from: sleemanj on March 11, 2019, 12:12:03 amIndeed. But don't forget the inductance of a wire, 1nH/mm being a rule-of-thumb. Hence a 6" wire (as commonly used with solderless breadboards) adds ~150nH.QuoteAnd don't forget to calculate the LC resonant frequency and see if it is anywhere in the circuit's/components' frequency response (N.B. not signal's frequency response!).

author: anbudroid
author_rank: Newbie
timestamp: March 13, 2019, 04:11:43 am
content: Quote from: Zero999 on March 10, 2019, 06:20:51 pmYes sir, my first picture shows the DC-DC Output voltage at the board level itself. am not think the problem is because of DD-DC . this problem persist even if I omit the DC-DC and plug the bench power supply directly to the breadboard.After reading all of the discussion and investing some times around the breadboard I finally convinced myself that breadboard are only worth to work with digital signals and non-precious analog circuits. if we want to test any project with confident, first thing is "say no to breadboard"because am not conscious about this kids of error previously when I work with switching applications . thinks create problem only when I need analog.

author: tggzzz
author_rank: Super Contributor
timestamp: March 13, 2019, 08:15:10 am
content: Quote from: anbudroid on March 13, 2019, 04:11:43 amDigital waveformsareanalogue signals, ones that areinterpretedby the receiver as being digital signals. If the analogue waveforms don't meet the input specification, the receiver canmisinterpret them.The only digital waveforms you are likely to encounter are in photon-counting and femto-amp applications.N.B. the frequency content of digital signals is determinedonlyby the risetime; the period is completely irrelevant. For a little theory and a practical demonstration, seehttps://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/Modern jellybean logic has frequency content above 1GHz. Work out the current required to change the voltage of a 5pF capacitor by 5V in 1ns (typical input/voltage/time). Now realise that a 2cm wire on a solderless breadboard has 20uH inductance. Finally work out the induced voltage v=Ldi/dt. And then you won't use solderless breadboards for digital signalsRead Bogotin's rules of thumbhttps://www.edn.com/collections/4435129/4/Bogatin-s-Rules-of-Thumb

author: Ian.M
author_rank: Super Contributor
timestamp: March 13, 2019, 11:15:40 am
content: Digital logic on a breadboard is not *THAT* bad - as long as you don't try to use faster logic than LS TTL and HC CMOS, and put the decoupling caps directly over or next to the chips, with their leads as short as possible into the holes closest to the Vcc and Gnd pins.Clock inputs can be a problem, but the typical CMOS input protection diodes clamp overshot fairly well, and if you control slew rate with source termination you can usually eliminate glitches on the active edge that would otherwise cause double clocking. Occasionally you may need to resort to source terminated twisted pair for a longer signal run, possibly with AC termination using a RC network at the receiving end to damp transients on the edges (100R + 22pF to 100pF). Data inputs aren't usually a problem, as long as the clock rate is low enough for ringing to settle out before the next active clock edge.It also helps if you are using a MCU with all the high speed stuff on one die, rather than a CPU with ROM, RAM and I/O spread over several breadboards.

author: tggzzz
author_rank: Super Contributor
timestamp: March 13, 2019, 11:38:06 pm
content: Quote from: Ian.M on March 13, 2019, 11:15:40 amI did specify modern jellybean logic, not mid-70s 40-year old families!Lead inductance in DIL ICs could be a serious problem in the mid 80s.Modern large devices are so susceptible they come with IBIS LCR specifications for each pin (including multiple Cs to different rails), plus the waveform for each different drive level.

author: anbudroid
author_rank: Newbie
timestamp: March 14, 2019, 06:31:22 am
content: Digital waveformsareanalogue signals, ones that areinterpretedby the receiver as being digital signals. If the analogue waveforms don't meet the input specification, the receiver canmisinterpret them.you are right sir , but beginners are not play more than 10Mhz clock signals with breadboard. and most of the Arduino players are much below this level.

author: radiolistener
author_rank: Super Contributor
timestamp: March 14, 2019, 07:35:48 am
content: I catch the same issue at breadboard which I bought on aliexpress. In my case, the root of cause was breadboard resistance. It leads to voltage drop down when circuit consumes a lot of current. In my case I was used high speed ADC with power consumption 300 mA. And voltage drop was about 0.3-0.6 V.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2019, 10:51:31 am
content: Quote from: anbudroid on March 14, 2019, 06:31:22 amSigh. That misapprehension never goes away.My step generator has ~1MHz period, and has significant energy content above 1GHz. The period iscompletely irrelevant; theonlything that matters is the transition time.If you want an anthropromorphic handwaving explantion, consider that when the signal has one edge, it doesn't "know" when the next edge is coming - it might be in 1ns, 1s, or never.For a little theory and some practical demonstrations, seehttps://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

author: rdl
author_rank: Super Contributor
timestamp: March 15, 2019, 04:40:59 am
content: Out of curiosity, tonight I wired up a little test. Using one of my 3M No. 318 boards I input about 5 volts at the left end of the upper rails, ran it across to the right side and down the vertical rails, then back to the left end of the lower rails, a distance of nearly 17" (about 430mm). Actually double that for the entire loop. This meant it also went through 4 jumper wire connections (22 gauge tinned solid copper wire).With no load, there was virtually zero voltage drop, maybe 1 mV at most. With two 47 ohm resistors in parallel as load (210 mA measured) I got about a 40 mV drop. This was from measuring directly at the input to the breadboard vs. measuring directly across the resistors.Just thought people might find that interesting. If I get a chance, I may send a square wave through and see what it looks like on the scope.

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2019, 10:44:14 am
content: Quote from: rdl on March 15, 2019, 04:40:59 amThen try knocking the breadboard and generally moving it in ways that you would do when experimenting with a circuit. See if anything changes.Wait a couple od days, and repeat.QuoteMeasurement technique is important, so document the source characteristics, the scope, and how you connect those to the UUT.

author: rdl
author_rank: Super Contributor
timestamp: March 18, 2019, 05:36:48 pm
content: A couple of pictures to look at. The square wave from my function generator is pretty sad, but for comparison purposes it'll have to do for now.10MHz square wave at entry to board (blue) and at 47ohm resistor load 17" away (yellow)20Khz sine wave (same situation, blue at entry, yellow at load)I'll add this in case my previous description wasn't clear.The voltages measured previously were at A and B across the rails. The signals are compared between points A and B. The resistor (47 ohm) was connected to the negative rail, not disconnected as in the picture. Two resistors in parallel were used for the voltage measurements.

author: tggzzz
author_rank: Super Contributor
timestamp: March 18, 2019, 08:33:30 pm
content: 14ns risetime <=> 25MHz bandwidth, so your scope isn't the limiting factor.I suggest you look at the output of a logic signal. For bonus points, insert two 6" breadboarding leads in between the scope/signal and scope/ground. The 15pF scope probe tip capacitance is similar to a couple of CMOS/TTL loads.

author: rdl
author_rank: Super Contributor
timestamp: March 19, 2019, 10:37:33 pm
content: I was not sure what more information another 6 inches of wire would add, after all, there is already ~425mm of conductor including 8 wire to board insertions, but I looked at it anyway.I don't actually see much difference.While I was at it, I measured the resistance of one 425mm length of breadboard rails (plus wire jumpers) at 18 ohms. If I did the math right, this agrees closely with the 40 mV voltage drop I recorded previously. The capacitance across the pair of rails (all 425mm) was measured as about 85 pF.

author: bd139
author_rank: Super Contributor
timestamp: March 19, 2019, 10:50:38 pm
content: A point to bear in mind when using or not using breadboards: Sometimes signal integrity and layout doesn't actually matter that much!I'm doing some sub 1KHz stuff with opamps at the moment which requires a lot of trial and error. I'm doing it on a 3M breadboard and am giving zero fucks

author: rdl
author_rank: Super Contributor
timestamp: March 20, 2019, 12:55:08 am
content: One more thing, and this is something that I've previously seen evidence of potentially being a real problem. This image is where the crosstalk is looked at on the long 425mm path. The blue trace is the actual signal on the "positive" rail (red jumpers), and the yellow is the induced signal on the "negative" (black jumpers) rail.Here the same signal is running through one of the five hole vertical strips (blue trace) with the crosstalk that appears on the adjacent five hole socket strip (yellow trace). Doesn't look that bad actually.I'd like to point out to anyone reading this thread that running a 10MHz signal through 425mm of conductor, including multiple wire to board insertion connections, is somewhere beyond "worst case scenario". I'm sure decent quality breadboards have a limit to their usefulness, but I don't know where it is and I'm not inclined to go looking today.

author: bd139
author_rank: Super Contributor
timestamp: March 20, 2019, 07:56:47 am
content: On that basis you could have some fun and use the power rails as a directional coupler

author: rdl
author_rank: Super Contributor
timestamp: March 20, 2019, 09:25:47 am
content: Here are the waveforms with and without the extra 200mm jump wire inserted after going through the full 425mm rail length. I previously said I didn't see much difference. Taking a second look, the one with the extra jumper is actually shifted slightly more. While definitely something to keep in mind, it's not likely to be a problem in any circuit I would build on a breadboard. Signal connections there should always be as short and direct as possible, not two feet long with multiple jumper wire breaks.

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2019, 09:38:33 am
content: Quote from: bd139 on March 19, 2019, 10:50:38 pmYup.A 1kHz analogue signal isn't going to have much energy above 100MHz. A 1kHz digital signal would, though.The other issues with analogue circuits are that that although your signal may only be 1kHz, it is quite possible for the circuit elements to have much higher frequency response. Remember the old adage: "amplifiers oscillate, oscillators don't"

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2019, 09:43:51 am
content: Quote from: rdl on March 19, 2019, 10:37:33 pmThat's still a well-controlled slow risetime, unlike that seen with jellybean logic. Even with that signal, you can see some oscillation at ~100MHz.I don't know how 100MHz compares with your scope's bandwidth, but a 100MHz signal on a 100MHz scope+probe would be 3dB down, i.e. only 70% of the actual amplitude.

author: bd139
author_rank: Super Contributor
timestamp: March 20, 2019, 09:54:08 am
content: Quote from: tggzzz on March 20, 2019, 09:38:33 amIndeed.I've seen a 2n3904 oscillating well into VHF (190MHz) on a breadboard. I assume it was due to the breadboard stray capacitance and collector wire inductance acting as a colpitts style oscillator. I played with it for a bit to see if I could tune it then gave up and shut it up by leveraging the miller effect with a 47pF across collector/base. I was establishing DC operating point of a circuit before I moved it in situ on a manhattan construction board.

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2019, 10:09:09 am
content: Quote from: rdl onTodayat 12:55:08 amI'm not entirely sure what you are showing there, since the detailed wiring matters.However, NEXT and FEXT on signals can be serious problems. (NEXT= near end crosstalk, FEXT= far end crosstalk). But I doubt the traces show those.More important is ground bounce, whichdoescause serious problems even on well-laid out multilayer PCBs. It isoneof the reasons that modern busses tend to be serial rather than the old-time parallel busses.Do the calculation using, say, a 3V signal swing with a 10pF load capacitance and a 2ns transition time, and a 6inch/150nH wire:current icrequired to charge a capacitor C through a voltage dV in time dt is ic= CdV/dt, so ic= 15mAvoltage Viinduced across a capacitor by a changing current dI in time dt is Vi= LdI/dt, so Vi= 1.125Vand you can multiply that by however many outputs are changing simultaneously!Obviously you can play around with the precise numbers until the cows come home, but having a +-1V signal "suddenly" appear on the ground/Vcc line isn't going to lead to operation within the IC's specification.

author: rdl
author_rank: Super Contributor
timestamp: March 20, 2019, 02:07:49 pm
content: Quote from: tggzzz on March 20, 2019, 10:09:09 am

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2019, 04:50:45 pm
content: Quote from: rdl on March 20, 2019, 02:07:49 pmI don't see what the lower scope probe's shield is connected to.I expect the solderless breadboard has wide internal connections, in which case they will have a lower inductance than a wire of the same length.

author: rdl
author_rank: Super Contributor
timestamp: March 20, 2019, 11:27:23 pm
content: Quote from: tggzzz on March 20, 2019, 04:50:45 pmIt was connected to the same place on the resistor as the other probe and function generator when the screenshot was taken. I had disconnected it and was probing around at various places on the breadboard to see where and how much of the signal I could pick up. The induced signal was about 500 mV larger with the scope ground disconnected.

author: Jwillis
author_rank: Super Contributor
timestamp: March 21, 2019, 07:05:18 pm
content: I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.The results were not really surprising but interesting non the less .The bread board 145mm rail had a resistance of 46.5 mOhms .The 145mm 26AWG wire had a resistance of 40.2 mOhms . Trace 1mm on the 1 oz PCB showed a 120 mOhm resistance.All conductive surfaces will exhibit a resistance .And this resistance will increase with distance the narrower the path and increases in ambient temperature.This is unavoidable. If your expectations don't include this unavoidable variable then your project is beyond the realm of conventional conductors and into superconductors.Keep your paths as short as possible when prototyping your design regardless if you use a breadboard or PCB proto-board.

author: iMo
author_rank: Super Contributor
timestamp: March 21, 2019, 07:22:27 pm
content: FYI - the capacitance between the 5pin segments is 3.5pF.

author: tggzzz
author_rank: Super Contributor
timestamp: March 21, 2019, 09:24:32 pm
content: Quote from: Jwillis on March 21, 2019, 07:05:18 pmAnd what was thevariationin the resistance (a) with different (diameter, oxidation, dirt) wires (b) with different holes (c) when something was dropped nearby on the bench (d) tomorrow?Often the absolute value isn't too important, but stability and predictability is important. I would expect soldered joints to be significantly better in that respect.

author: Jwillis
author_rank: Super Contributor
timestamp: March 22, 2019, 12:44:40 am
content: Quote from: tggzzz on March 21, 2019, 09:24:32 pmIndeed its a static experiment .It wasn't meant to include other unforeseen variations as you describe.But it does have conclusive evidence that the rails resistance is not much more than a piece of wire yet much less than a PCB .Breadboards are not intended to be used as a final construction and I would agree that they have their own inherent draw backs .But soldering ,desoldering and resoldering over and over can have its own inherent draw backs as well .Component damage and wasted resources being at the top. Bread boards ,as mentioned before, have been used for years and years for experimentation prior to prototyping.Although today there are simulators but they have limitations as well like variations in component performance that may not seem apparent until a rough mock-up is put to a test.If some feel that the use of a breadboard is not in their best interest for experimentation so be it.The majority list them as one useful tool essential to experimentation.But like any tool proper use and maintenance is important as well.

author: rdl
author_rank: Super Contributor
timestamp: March 22, 2019, 01:46:38 am
content: Quote from: Jwillis on March 21, 2019, 07:05:18 pmYour measurements are not too different from mine, yet the op was seeing more than an order of magnitude higher voltage drop. It seems there almost has to be something not right with either his board or the connections.

author: Jwillis
author_rank: Super Contributor
timestamp: March 22, 2019, 06:26:05 am
content: More information on the step down converter might help. I would guess that its not preforming as required.Although so many amps may be supplied to it does not mean that's what you'll get out.Even small amounts of resistance can cause voltages to drop out when theirs not enough current supplied.Any circuit will only draw as much current it requires .But if the current isn't there the voltage will drop.

author: tooki
author_rank: Super Contributor
timestamp: March 22, 2019, 12:12:02 pm
content: Quote from: rdl on March 22, 2019, 01:46:38 amDefinitely. As I said earlier, I've got a few chinesium breadboards that have several ohms (!) contact resistance. (And many more that are just fine, in the dozens of mOhms like yours.) I've marked the bad ones. They're OK for really simple stuff like testing LEDs, but I don't use them for any real circuits. I suspect the OP has a similar issue.Additionally, some of those chinese "dupont" jumpers have poor connections or wire, and have excessive resistance, too.

author: Ian.M
author_rank: Super Contributor
timestamp: March 22, 2019, 01:34:42 pm
content: Can you test your crappy chinesium breadboards with a magnet? It would be interesting to find out if the problems with them are due to the use of steel contact strips.

author: tooki
author_rank: Super Contributor
timestamp: March 22, 2019, 03:25:56 pm
content: Quote from: Ian.M on March 22, 2019, 01:34:42 pmJust checked, does not appear to be magnetic at all.

author: rdl
author_rank: Super Contributor
timestamp: March 22, 2019, 04:34:02 pm
content: I have a lot of breadboards I've acquired over the last 30 years or so. There are quite a few I would describe as cheap junk, but only one is magnetic. It's a green mini size one that I had added my last ebay order of cheap stuff from China just to see if it was any good.https://www.ebay.com/itm/5-Color-Mini-Solderless-Prototype-Breadboard-170-Tie-points-For-Arduino-Shield/201677166530

author: Jwillis
author_rank: Super Contributor
timestamp: March 22, 2019, 07:33:25 pm
content: I only have one that I know is from China the rest are from North American suppliers with unknown origin.I tend to be a cheap son of a gun because my just a hobbyist.But non exhibit magnetic properties and all have similar resistance of approximately 0.5 - 1 mOhm between each socket.But magnetism might not be conclusive either because they may have nickel plating.I suppose my next order from Digikey I'll breakdown for a brand name one and see if theirs a difference.Aside from a few decade counters and timers most of what i do is mostly power electronics so my experience is admittedly limited.But I would definitely check that convertors output.