While I don’t revel in piling onto the criticism, and I absolutely do not want to discourage you, you did ask for feedback, so here goes:
A couple of months ago, designed some custom test leads for a solderless breadboard. They are 4mm Banana plug to male Dupont 2.45mm test leads.
Sorry what?
Do you mean 0.1” (2.54mm) pitch? Your cables do not allow for a 0.1” pitch, the grips are much too big. Pitch is the spacing between pin centers.
DuPont pins are 0.65mm in diameter
No. They are square, 0.025” (0.635mm) on each side.
the test leads are approximately 0.8mm. They fit perfectly in a breadboard and I haven’t had any issues with them bending.
The diagonal of a 0.635mm square pin is about 0.8mm, but when you insert those into a breadboard (which is already at the outer limits of what goes in them comfortably: on expensive breadboards they can be tough to insert, on cheap breadboards it stretches the contacts), you’re not doing it at a rotation where the diagonal is perpendicular to the contact axis.
Upshot is, if you’re designing something expressly for breadboard use, I’d shoot for 0.5-0.6mm diameter, and it needs to have tapered points or you’ll never get them in. (I’ve encountered Chinese breadboard jumpers with 0.5mm round steel pins, which would be great if they were tapered, but they’re not, so they often just snag.)
I agree that I should use a thinner wire.
I am planning on designing a second revision of the breadboard test leads. On the new design, I’m going to use a smaller wire gauge (20 or 22 AWG).
Why so huge? Breadboards aren’t intended for huge currents. 24AWG is more than enough, comfortably.
I’m considering changing the wire material from PVC to silicon. Since silicon is more flexible and easier to work with.
Well, silicon is a hard, brittle element. It’s not flexible in the slightest.
You mean silicone, and indeed I do prefer using silicone wire for breadboards. But more important than the insulation material is the wire stranding: 24AWG stranded wire can have as few as 7 strands and as many as 128 (like Kabeltronik LiFY). This makes a
massive difference in how compliant and limp a cable is. Not all silicone wire is made for flexibility. Also bear in mind that silicone has inferior abrasion resistance than PVC, and the surface tends to hold onto dust. So a super fine stranded PVC may be superior in some respects. I’d take that over low-grade silicone wire any day. The good Chinese silicone 24AWG I mention later has somewhere around 40 strands.
Also, do you think $17.98 is a reasonable price for a set of test leads?
If it’s a top-quality product in every respect then that is reasonable. (Top quality banana plugs cost $2-3 apiece, so that gives a sort of context. Hirschmann, a top-quality German manufacturer, sells a banana to female DuPont cable, made with ultra fine stranded 24AWG wire, for around $6-7 apiece. They don’t make one with male pins at all, alas.)
Have you measured the contact resistance of your cables? Cheap banana plugs often do poorly here, so that’s one thing you wanna check yours for. (Another is longevity: do the lanterns weaken over time? Cheap ones do after a few hundred insertions, whereas a Stäubli or Hirschmann lantern plugs remain as good as new even after decades of use. I have some that are likely 30+ years old and still work like new.)
I’ve attached some photos of a few cables I’ve made for breadboard use: the one with the banana plug is a 0.8mm pin intended for high-density D-sub connectors (like the HD-15 used for VGA). Even with the lovely torpedo-shaped point, they are quite difficult to insert into a 3M breadboard. Those pins aren’t intended for individual use, so I wrapped it in numerous layers of heat shrink to make a grip. It’s just baaarely within the 0.1” envelope. The plug is a Stäubli (top quality Swiss brand) stackable plug. The wire is French-made 24AWG test lead wire from Cal-Test, but honestly I don’t like the wire: it “takes a set” too much, so it’s always creased, and the surface is super rubbery (not slick like good test lead silicone). I don’t use those much, either, because of the insertion force required.
Next are two bundles of jumper wires made with delightful 24AWG silicone wire from China (from a specific supplier, they’re not all this nice). The male pins are good quality Chinese “DuPont” contacts, but the female ones are made with genuine ultra-high-force Mini-PV contacts from Amphenol. Chinese DuPont female contacts are looser to begin with and loosen a lot more after a few insertions, whereas the genuine Mini-PV are specified at 1000 cycles, and the ultra-high-force versions are expressly designed for use as single connectors. Despite the Mini-PV contacts costing upwards of 10x as much as Chinese contacts, their vastly longer longevity and the aggravation they prevent makes them well worth it.
The thinner red jumper on its own is one made with 28AWG Chinese silicone. Absolutely lovely for breadboard use.
Last but not least, I’d be remiss if I didn’t mention that Pomona sells its model 4691 banana to pin adapters. They come in a few sizes, the smallest being this, the 0.8mm. They have rounded points (more or less hemispherical), and they’re significantly tougher to insert than the aforementioned torpedo-shaped HD pins. The 4691’s shaft is bendy, so you don’t have to have your fat banana cable’s weight dangling from the breadboard. But honestly, I never use them.
I much prefer my homemade leads made with Chinese silicone with crimped male DuPont pins on one end and a soldered Stäubli or Hirschmann banana plug (for permanent installation) or a screw-mount Pomona 1825 or spring-loaded WAGO 215 banana plug (for temporary cables) on the other end.
I’ve also experimented with making jumpers with TE MQS contacts. The housings are 0.1” pitch multi-pin automotive monsters, but using heat shrink does work. The pins are 0.025” square just like DuPont. As automotive connectors, they’re very robust: the male contacts are actually a solid pin (like a PCB header) welded onto the crimp terminal. The female ones are luxurious to insert onto a pin. The downside is that they’re a bit fatter than DuPont contacts, so by the time you’ve put heat shrink onto them, you’re just a bit above 0.1”, so you can’t line them up on adjacent rows. 2 or 3 will work, but beyond that it gets tight real fast.
I just tested the Test Leads, and they seem to both fit in the holes next to one another (it’s a snug fit). The molded strain relief is flexible, which helps out a lot.
The real problem begins when you need more than 2, or when other components or plugs are adjacent. (It’s not uncommon for me to have 4 or more DuPont pin cables going off the breadboard: 2 or 3 for power supply, then 2 for a voltage or current measurement, sometimes more to a second or third meter.) DuPont pins in DuPont housings are designed to fit within the 0.1” pitch and can be lined up in any number.
As you can probably tell, I’m quite the connector junkie, and put a lot of thought and care into my test leads, so I absolutely understand your motivation for wanting to make these leads. But I do think a bit more thought needs to go into the design, because I don’t feel your design quite yells “I really understand the use cases and constraints”.