Stupid question about DIY test leads - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: April 11, 2020, 10:29:50 am
content: I would be happy to DIY my own test leads and can imagine what i would do for the cable and handle but what can you do about the test lead itself?Thicker sewing needle?

author: t1d
author_rank: Super Contributor
timestamp: April 11, 2020, 12:01:49 pm
content: An easy solution and readily available/free part would simply be a scrap pin, cut from a component, or a single header pin. I use single header pins, all the time, to make the probe for PCB-style test gear... Like a DIY Logic Probe... The PCB serves as the handle. The front end is tapered to a point and the pin is attached to an enlarged pad, placed on the tip of the point. To avoid having to bend the pin to be horizontal to the board, just use an SMD pad, instead of a through hole.

author: Rerouter
author_rank: Super Contributor
timestamp: April 11, 2020, 12:15:26 pm
content: Depends what your connecting to, for 0.1" headers I bought some terminals for automotive connectors that took the same terminal but with a much higher cycle rating, crimped them to my test wire and fitted heat shrink over them, they stay connected better than the dupont leads, and can pack more tightlyFor others, I ground nails to a rounded point, sanded them shiny then coated them in solder, attached a test wire at about half length, coiled some of the wire around the top of the nail for strain relief then fitted glue lined heat shrink, have been my most reliable set of test leads so far, and I can tack them in place when testing things (dont recall what metal, but they are the small nails, like 20mm long)For alligator clip leads, there is a big difference in quality out there, the cheap ones you can barely even press open because the rubber spins so easily, other ones barely open etc, we managed to get our hands on an old bucket of test lead parts including high quality clips a few years back,For your wire, the higher strand count the better, avoid solder getting under the insulation or past any strain relief, and choose suitable thickness for the current, a lot of the alligator clip leads rubber ends will melt at 8+ amps,for weirder leads, work with what you have, if your using the same gear over and over again, try and get a dead one and make a connector harness into a test loom, in the extreme cases you can make up PCB's with pogo pins soldered to it and the plastic clip on pcb spacers for the existing mounting holes to make easy diagnostic boards.

author: t1d
author_rank: Super Contributor
timestamp: April 11, 2020, 12:18:25 pm
content: More random thoughts... A sewing needle is not engineered to be low resistance. This could effect your readings. Even the resistance of a header pin needs to be considered, for super accuracy, or use with tiny voltages/currents.And, a sewing needle is not intended to be soldered. Soldering it is likely to make for a struggle. Keeping heat on it to try to get it to take solder could lead to lifting a pad off of the board.I have some extra long header pins, just for this purpose. I bought some very small diameter heat shrink that I use to cover them. I just leave the very end exposed to make contact. So, I end up with a long, narrow pin that is easy to work in among all the components on the board and it is insulated to prevent shorts.I like Samtec HTSW-150-29-T-S, for this purpose. The plastic on these is made to handle higher heat. They don't melt so easily.

author: t1d
author_rank: Super Contributor
timestamp: April 11, 2020, 12:22:47 pm
content: Quote from: Rerouter on April 11, 2020, 12:15:26 pmWell, that's just down-right clever! And, the solder coating negates any connectivity issues. Good job.

author: t1d
author_rank: Super Contributor
timestamp: April 11, 2020, 12:25:57 pm
content: MP3, I see that you are in the USA. If you are in the lower 48 States, I would send you some of the Samtec pins to try... Free, of course. Just send me a private message with your mailing address.

author: Mp3
author_rank: Frequent Contributor
timestamp: April 11, 2020, 10:38:38 pm
content: Some really cool ideas(and generosity!) here. Thanks guys.I found some copper soldering tips i forgot i had. No idea when i bought them, maybe i can repurpose them into test leads. Lol

author: Mp3
author_rank: Frequent Contributor
timestamp: April 12, 2020, 10:07:43 am
content: These will have to do until my new Fluke’s get here and I can chop up the connector to fit my bench meterDon’t remember where I put my box of heatshrink though, so just a light kapton wrap for now.Seems nice and stable at 0.4 ohms on each lead. It’s nice speaker wire after all.I knew I saved those copper tips for a reason

author: Ian.M
author_rank: Super Contributor
timestamp: April 12, 2020, 10:27:55 am
content: To make a cheap sharp probe, you can dismantle a used up Bic Crystal biro, pull off the empty ink tube, wash the remaining ink out of the tip then punch the actual ball out of the brass part of the tip using a pin from the inside. Then you can take a thin gold plated sewing needle, solder it into the brass part with a few mm protruding, solder the test lead wire to the needle eye , fit the plastic collar over the wire and reseat the brass part in it, then re-fit the tip to the body, taking the wire out through a hole drilled in the end plug.Don't use a plain steel sewing needle - they are very hard to solder successfully without the gold 'flash' aiding wetting. Properly soldered, the resistance from wire to needle point will be a small fraction of an ohm. If you are going to keep the leads in a toolbag, and don't want to stab yourself, keep the biro cap!Caution: The Bic Crystal biro bodies are fairly brittle and have a tiny vent hole, so don't treat them roughly or use them for probing high voltage circuits.

author: Mp3
author_rank: Frequent Contributor
timestamp: April 12, 2020, 11:32:40 am
content: Quote from: Ian.M on April 12, 2020, 10:27:55 amSuch a cool idea!

author: wizard69
author_rank: Super Contributor
timestamp: April 12, 2020, 06:02:11 pm
content: DIY test leads can be just about anything, the only thing is that they need to be user safe. Test lead wire itself can be bought in just about any length but in a pinch almost any wire can be used. Of course any flexible wire could be used in a pinch If you are tying meters together semi permanently even building wire can be used for those long term connections.For test probes tips you ultimately need to use steel for all of its positive properties. That is sharp, fine points, that can probe tightly spaced pins on today's electronics. If you have serious reservations about conductivity then plate the steel with a conductive material. This is where sewing needles and similar high quality steel pins become valuable in DIY probes as such are the only premade materials that are easy to get and meet the required parameters. If you have a machine shop of course you can machine whatever you want.if your interests are move electrical you can use brass for the probes tips. In fact many commercial probe tips are made out of brass but the tips are normally bulky. On the flip side you can buy brass in round bars fairly easy. Even braising rod could be leveraged in this case. Finding premade brass items similar to sewing needs is a lot harder though; you might find brass pins or nails at a hardware store. One possibility is to make use of crimp style pins for use on circular connectors, but at this point you might as well buy your test probes unless you have a supply of such pins.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: April 14, 2020, 03:59:20 am
content: Maybe look at those:https://www.eevblog.com/forum/testgear/useful-adaptor-techniques/msg1223935/#msg1223935

author: Mp3
author_rank: Frequent Contributor
timestamp: April 14, 2020, 07:07:31 am
content: Quote from: Neomys Sapiens on April 14, 2020, 03:59:20 amThese look really nice.Thanks for sharing.