It's the weekend, need to build a sensitive magnetometer in time for Monday...

Here's are the constraints:

1. Can't order anything in for delivery on the weekend (digikey/mouser etc. are out), and our local supply houses are useless, can't get delivery till Tuesday at the earliest (1 day after the deadline)

2. Has to be quick to prototype

3. None of the big guys stock magnetometer sensors that are adequate for the needs anyway, these are specialist sensors and I'd need to wait.

4. Can be breadboarded initially to test, but due to the sensitive nature of the coils, things need to be locked down on a PCB (which can't be ordered in, in time for Monday)

Rapid prototyping MacGyver style, I need to get creative. Found some very old approx 35 gauge (0.15mm) magnet wire and some larger mystery magnet wire in the wire box. I must have purchased it 30 years ago when I first started electronics and was wrapping AM Radio ferrite rods.

I have an othermill, so at least I can prototype PCB's fast.

I've been desoldering everything with any type of ring core or ferrite core in from my stash of kept PCB's from old equipment. Old Motherboards, switched mode PSUs and router boards proved fruitful.

They are all mystery cores, tried investigating online to see if the color indicated the core material, but it doesn't. Some of the coils had numbers on, but most were made in China and old, so none resulted in a data sheet :-( Here's the resulting stash: