Stupid Octopus question - Page 1
Forum section: electronics / beginners

author: DPotts245
author_rank: Newbie
timestamp: February 12, 2024, 10:12:18 pm
content: OK,New member here and I've got what I'm sure is a stupid question but I'm currently stumped.I built an octopus a few years ago. It's the small gray box under the top shelf in the photo. I moved to be near the grandkids and my bench spent a year or so in storage. I've got it set up again recently and found my octopus was giving me some crazy readings. Like a moron I disassembled it (without taking photos) thinking something was bad on the little board I used. Everything checked out so I proceeded to build another.There are still unresolved issues regarding the readings but I'll save those for another post. My stupid question for today is what do the BNC connectors in the octopus get grounded to? I've breadboarded the octo trying to sort it out and I'm at a loss.The attached schematic is the one I'm using except I run it off of an Elenco AC/DC power supply I built from a kit years ago.

author: Ian.M
author_rank: Super Contributor
timestamp: February 12, 2024, 10:17:52 pm
content: They don't have to be grounded to anything for the octopus to work, just connected together and to the black probe, but if you include the mains transformer in the box, they should be connected to mains ground and to the transformer core for safety.

author: DPotts245
author_rank: Newbie
timestamp: February 12, 2024, 10:26:40 pm
content: Thanks for the quick reply.I had both BNC's grounded somehow in my original box. I must have grounded to the black probe.and I have no idea why the first photo turned on it's side.

author: p.larner
author_rank: Frequent Contributor
timestamp: February 12, 2024, 11:39:42 pm
content: are you powering the test leads with ac or dc?.

author: DPotts245
author_rank: Newbie
timestamp: February 13, 2024, 12:02:18 am
content: Quote from: p.larner on February 12, 2024, 11:39:42 pm6.3V AC

author: CaptDon
author_rank: Super Contributor
timestamp: February 13, 2024, 01:56:55 pm
content: I have never heard that circuit called an octopus? P.Larner, looking at the schematic it is obvious A.C. as the leads go to the transformer with no diodes in sight. We made good use of the commercial version featuring selectable voltages, currents and frequencies with a built in C.R.T. display. The Huntron Tracker, various models.

author: wasedadoc
author_rank: Super Contributor
timestamp: February 13, 2024, 06:39:56 pm
content: Quote from: CaptDon on February 13, 2024, 01:56:55 pmPut "octopus tester" into a search engine and it will return lots of hits.

author: Gyro
author_rank: Super Contributor
timestamp: February 13, 2024, 06:47:39 pm
content: Yes, the Octopus is a venerable and handy little basic curve tracer...https://www.eevblog.com/forum/beginners/dirt-cheap-and-simple-scope-based-component-tester-curve-tracer/You can always rely on somebody to poke it to death with their digits though!https://www.nutsvolts.com/magazine/article/build-an-oscilloscope-octopus

author: themadhippy
author_rank: Super Contributor
timestamp: February 13, 2024, 06:48:25 pm
content: Quoteshouldn't cost more than six quid to get it sorted