A weird breadboard contact resistance problem. - Page 1
Forum section: electronics / general

author: analogueAdder
author_rank: Contributor
timestamp: May 24, 2020, 10:45:39 pm
content: I encountered this odd and unexpected problem and made a video about it.Now I'm thinking of buying some higher quality breadboards and I'm thinking of 3M but I'm still not sure.Has anyone else encountered this before?

author: Ian.M
author_rank: Super Contributor
timestamp: May 25, 2020, 12:05:14 am
content: Its not particularly clear from your video what your problem was as you appeared to have great difficulty getting stable repeatable readings when probing round your breadboards. Also for %DEITY%'s sake, SAY WHAT YOU ARE DOING, what readings are, etc. If English isn't your first language and you are unhappy with your spoken English, you may prefer to subtitle your videos, or for readings, edit in a closeup of the DMM display, overlaid in the corner etc.You either need good quality croc-clip adapters for your probes to go onto component leads, or short adapter leads terminated in gold plated Dupont pins or similar, or best yet, good quality 4mm banana plug to Dupont pin leads, which avoids the extra contact resistance problem of adapters. Although probing around is the most convenient for quickly locating a problem area, when you want to take a reading to share with others or for your lab notebook, to get stable results, take it hands off - i.e. connect the leads then take the reading without touching the circuit.There are a few breadboard traps for the unwary (apart from their generally poor performance at higher frequencies due to inter-strip capacitance and lead inductance):Some long breadboards have split bus rails, and if you want end to end continuity, you have to install a jumper over the gap in the middle. This is usually indicated with red and black or blue lines along the bus rails with a gap in the middle where the split in the rail is, but some breadboards may have split rails with no or continuous rail markings so always check a new breadboard with a multimeter!Cheap & nasty breadboards are generally problematic, mostly due to poor quality contacts, that often require grossly excessive initial insertion force, then distort and fail to hold reasonable contact tension, or even block the hole. The contacts are made of mystery metal - often mild steel 'flash' plated with low grade brass, nickel or tin, so are very vulnerable to corrosion if the board is exposed to atmospheric or other contamination + high humidity.Perhaps the most irritating fault is if the bus strips aren't made with a single un-cut strip of contact groups, but instead are two or more strips with a butt-joint between them, that typically goes high resistance.Using a breadboard for more than 50V, 500mA is insane, and in practice, its better not to exceed a few hundred mA through *ANY* breadboard contact, even good quality ones. Also if you don't want to melt the plastic shell, don't exceed 1/3 of the wattage for any resistor, 1/2 W for any un-heatsinked TO-220 package, and derate the power rating of other semiconductors by at least 50%!Cheap Dupont pin jumper wires are *EVIL* - use 24AWG solid hookup wire, cut to the actual length required.

author: analogueAdder
author_rank: Contributor
timestamp: May 25, 2020, 02:07:24 am
content: Quote from: Ian.M on May 25, 2020, 12:05:14 amThat's the problem I'm talking about. Three of the breadboards I tested where supposed to be made by Wish and I was expecting them to be decent. However, the best connection I could get had a resistance of 0R4!That's literally the lowest resistance I could get, I even tried to secure wires to the leads with the banana jack adapters (I'm using what I have at hand), and measuring the resistance hands off but the connections where just as erratic...Quote from: Ian.M on May 25, 2020, 12:05:14 amI know and have been using solid cooper wire for years.Anyways, I would like to thank you for your speedy reply and would like to ask for breadboard recommendations as these are not as good as the Wishboards that I remember.

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2020, 08:38:53 am
content: Quote from: analogueAdder on May 25, 2020, 02:07:24 amSolderless breadboards are the work of the devil, for many more reasons than those you have rediscovered. I refuse to touch them since I know I will spend more time debugging the breadboard than my circuit.Much better to use the techniques the masters use, especially manhattan. FFI this isa starting pointand there are many more resources out there.

author: analogueAdder
author_rank: Contributor
timestamp: May 25, 2020, 07:32:18 pm
content: tggzzz: I haven't touched wirewrap for over a decade! And I should get myself the required tools, prefboard, and wire...Goddammit, I feel old now...

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2020, 08:08:14 pm
content: Quote from: analogueAdder on May 25, 2020, 07:32:18 pmThe wire is easy, but the other items are expensive.More importantly, with todays' jellybean logic the wirewrap pins act as transmission line stubs - not good!(Realise that 74lvg1g* gates have <1ns risetimes - I can use them to get a clean 2.5V <300ps transition in a 50ohm cable)

author: trevatxtal
author_rank: Contributor
timestamp: May 26, 2020, 08:05:40 am
content: The use of WD40 or any Silicon containing spray on low voltage circuits has a lot to answer.Maybe not this problem but has caused many problems in the past.

author: Ian.M
author_rank: Super Contributor
timestamp: May 26, 2020, 08:17:48 am
content: Regular WD40 is silicone free, although I certainly wouldn't want it contaminating any light-weight contacts. Silicones are only a significant problem for non-sealed contacts that make/break under load, but if you are using e.g open frame relays, you shouldn't even use spray silicone furniture polish the other side of the same room or in rooms sharing a ventilation system. Apart from gunking it up, dunking a clean breadboard in silicone oil would cause no problems except causing any dust its exposed to to stick.

author: srb1954
author_rank: Super Contributor
timestamp: May 29, 2020, 06:13:38 am
content: Many years ago when I was designing equipment for telecom applications the customer banned the use of silicon grease or thermal paste for heatsinks because of the migration of the silicon oils onto relay and switch contacts within the same cabinet.