Faraday Box Project

Thread Starter

SamR

Joined Mar 19, 2019
3,179
@OBW0549 Finally got off my duff and finished it. Been putting parts together for over a year and changed the design a few times. Went for plug and play. 2 BNCs to small shielded coax for Sig Gen inputs or frequency output. 2 BNCs for scope probes. 10 banana jack sockets for power, multimeters, etc. connections. Still need to fab the interior wiring using flexible silicone rubber #20 wire to either header pins or mini grabbers. Large enough to fit a full size breadboard (or 2) and 2 scope probes. Checked grounding continuity on the BNCs and all grounded and case grounded with banana cable to PSUs safety ground or I can leave it floating. Very pleased the drilling of the thin metal went as well as it did. Had to deburr a bit with the Dremel but no real deformation. Also already centerpunched to add more sockets if wanted. Ran into some problems trying to work with Op Amp uV levels with all the EMF interference so it put a burr under me.
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KeithWalker

Joined Jul 10, 2017
1,581
Looking good! It should work well. You may need to re-adjust the HF response of your scope probes. I like the coffee on the front - very inspirational.
Keith
 

Thread Starter

SamR

Joined Mar 19, 2019
3,179
Yes, if you want to connect it or you can leave it floating. If you connect to the scope it is also grounded so to prevent ground loops the chassis ground can be disconnected. I use stacking banana plugs so every time you connect a meter all of the grounds are stacked so it only has one grounding point than can be connected to earth ground or left floating. The scope is the only instrument that absolutely has an earth grounding.
 

Thread Starter

SamR

Joined Mar 19, 2019
3,179
Finished the interior with #22 silicone rubber insulated wire to header pins. All of the wiring is "bolted" onto the sockets so changing it will be a simple task if I want a longer wire or a mini grabber instead of a header pin. One ground socket also connected to the chassis for earth grounding and I have a second floating ground socket. All other banana sockets insulated from the chassis.
 

DarthVolta

Joined Jan 27, 2015
521
Nice. I made a wooden tray, to slot breadboards into. And added a big copper wire to attach all the GND clips to. I get put off by the sight of a wire rat's-nest and clutter/parts everywhere....I sewar I'd do more EE if it wasn't for that...I need more bin's/etc.
 

OBW0549

Joined Mar 2, 2015
3,566
One thing you may want to do, for better electrical contact between box and lid, is to remove the paint from the outer rim of the box (chemical paint remover, sandpaper, emory cloth, etc.) where the lid contacts it as well as removing the varnish from the inside of the lid in that area.
 

Thread Starter

SamR

Joined Mar 19, 2019
3,179
se some feedthough capacitors for the power connections:
Interesting... I did think about how to attenuate EMI getting into the banana cables to and from the power supply and multimeters and didn't have a good answer other than to keep them short or shielded. Problem with banana jacks is grounding the shield.

EDIT: Dang they are expensive! DK only keeps 4 in stock and @ ~$100 ea. And... I threw a bunch away that I did not know what they were. ~40 years ago a retired military ex-electronics HF Radio tech who had gone blind gave me boxes of parts he had that had several of them in it that I didn't know what they were and threw out years later when cleaning up my mess at the time. They seem to be more for higher voltages in high RF exposure environments than what I am doing.
 
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Thread Starter

SamR

Joined Mar 19, 2019
3,179
I get put off by the sight of a wire rat's-nest
Still kinda have that problem. The 2 larger black wires are some miniature 50Ω coax that has a solderable braided shield instead of aluminum foil that is grounded to the box. The Sig Gen is not earth grounded so it only has one ground point when the box is grounded. The backs of the banana sockets have threaded rod w/ nuts and a solder lug for the wire connection so they can be easily changed if need to. One is a Palomar socket that is grounded to the box to connect earth ground to it or not. The rest are the better of the cheap chinesium variety and those were somewhat hard to find. They make really some crappy ones in china that are truly pitiful. I had a couple of these strip their threads when tightening the nuts on them so they could certainly be improved on. Certainly not up to Palomar quality. I decided to terminate with header pins instead of mini grabbers but can easily add them if needed.
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Audioguru again

Joined Oct 21, 2019
2,833
I gave up using a Mickey Mouse solderless breadboard many years ago and used parts soldered onto a compact stripboard circuit ever since. All my input cables are shielded. Then I never needed a Faraday cage to block interference. I never tried using parts at random, instead I designed my circuits to work properly.

My job was making custom one-of-a-kind audio circuits and my prototype built on a stripboard was frequently sold as the finished product.
 

Audioguru again

Joined Oct 21, 2019
2,833
The capacitance between all the rows of contacts and wires all over the place frequently cause an amplifier circuit to oscillate and a radio circuit not to work.
The faraday cage shielding has nothing to do with it, it simply blocks interference.
 

Thread Starter

SamR

Joined Mar 19, 2019
3,179
Which I am experiencing especially at mV or less levels... There are still a bunch of wires in the box that could cause problems.
 
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