Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I needed a rail-to-rail op amp in a DIP package to breadboard the amplifier for those toroids and came up dry, so I sawed out a protoboard square, glued a MAX4330 in SOT23-5 atop it in classic dead-bug style, rearranged the leads into the standard DIP pinout, and moved on:
MAX4330 dead-bug style on DIP adapter
The trick to getting the header pins aligned is to stick ’em in a pile of perfboards, which instantly makes them stand up straight and parallel:
Then wound them with grossly excessive amounts of wire (the up-armored core on the right appeared earlier):
Slit Ferrite Toroid current sensors
The smaller toroid is an FT37-43 that barely covers the active area of an SS49-style Hall effect sensor, but experience with the FT50 toroid suggests that’ll be entirely enough:
slit FT37 toroid trial fit to SS48-style Hall effect sensor
Data on the uncut toroids:
Property
FT50-61
FT37-43
Outer diameter (OD) – inch
0.50
0.375
Inner diameter (ID) – inch
0.281
0.187
Length – inch
0.188
0.125
Cross section area – cm2
0.133
0.133
Mean path length (MPL) – cm
3.02
2.15
Volume – cm3
0.401
0.163
Relative Permeability (μr )
125
850
Saturation flux G @ 10 Oe
2350
2750
Inductance factor (AL) – nH/turn2
68.0
420
Those overstuffed windings improved the sensitivity, but increased the winding resistance far beyond what’s reasonable.
Data on the slit toroids:
Toroid ID
FT50-61
FT37-43
FT50-61
Measured air gap – cm
0.15
0.15
0.17
Winding data
Turns
120
80
25
Wire gauge – AWG
28
32
26
Winding resistance – mΩ
530
920
100
Predicted B field – G/A
872
660
163
Hall effect sensor @ 1.9 mV/G
Predicted output – mV/mA
1.7
1.3
0.31
Actual output – mV/mA
1.9
1.9
0.37
Actual/predicted ratio – %
+12
+46
+19
The last few lines in that table show the transimpedance (transresistance, really, but …) based on the winding current to Hall sensor output voltage ratio (in either mV/mA or V/A, both dimensionally equivalent to ohms), which is why the toroid’s internal magnetic flux doesn’t matter as long as it’s well below saturation.
Gnawing the 80 turn winding off the FT37-43 toroid and rewinding it with 15 turns of 24 AWG wire dropped the winding resistance to 23 mΩ and the transimpedance to 0.36 mV/mA:
FT37-43 with 15 turns 24 AWG – Hall sensor
However, applying a voltage gain of about 28 (after removing the sensor’s VCC/2 bias) will produce a 0-to-5 V output from 500 mA input, which seems reasonable.
The first Wouxun (evidently pronounced “ocean”) KG-UV3D HT spent a month or two in my bike, lashed to a kludged version of the APRS+voice interface box and powered by its own lithium-ion pack. After I got the circuit worked out and built a duplicate, I picked up a second HT for Mary’s bike; as a result, that battery pack never got much use.
A pair of discharge tests shows the difference:
Wouxun 7.4 V Packs
The 2011-03 battery has almost exactly the rated 1.7 A·h capacity, at least if you’re willing to run it down to 6 V, and the 2012-06 pack delivers 1.9 A·h. Electronic gadgets measure state-of-charge using the battery voltage, so the older pack “looks” like it has much less capacity: it runs about 100 mV lower than the newer pack out to 1.2 A·h, then falls off the cliff. Looks to me like one of the two cells inside is fading faster than the other; so it goes.
I’m still thinking of using these to power some LED taillights, because they have a nice form factor and built-in latches:
Mary’s been picking blueberries and freezing them for winter treats, a process that involves inspecting each berry laid out on the tray.
This one failed QC:
Blueberry with eggs – overview
A closer look shows some remarkable structures:
Blueberry with eggs – detail
Unfortunately, they’ll probably turn into Brown Marmorated Stink Bugs. This is not a Good Thing, because those stink bugs will devastate fruit harvests, including all the apple orchards along the entire Hudson Valley, over the next few years.
They may be Predatory Stink Bugs, which would be unusual in Dutchess County, but not nearly so awful.
We are very much interested in some of your product. We try to contact you online but you are not online so we decided to attach the picture of the product we need to dropbox and put it in your offline. Open the bellow link and download the attachment to preview the product we need:
... dropbox url snippage ... /Product%20Pics.rar
Let me know if the product is still available for sale and how much it costs, also tell us the product details.
Regards,
Allen Moore,
Procurement Officer,
International Product Buyers
Well, I don’t generally rebuff the humble, but I don’t have any “product” for sale. Also pulling the suspicion trigger:
To: Recipients <Procurement@Officer.com>
Subject: Open Attachment For Product Picture
It’s not clear what “attach the picture of the product we need to dropbox and put it in your offline” might mean. Despite the Dropbox URL, the email sported an attachment named Product\ Pics.rar, showing they come from a different universe wherein every operating system has a native RAR extraction program.
Being a dutiful citizen of the Interwebs, I did what the nice man asked:
unrar e Product\ Pics.rar
That produced a single file which RAR described thusly:
Extracting Product Picjpg.SCR
At least that’s what it looked like on the command line. I think they were trying to overwrite the SCR with the jpg, as the file name was really Product Pic<U+202E>RCS.gpj, but the Unicode U+20E bidirectional text control character seems to be in the wrong place. I think they wanted Product Pic.SCR<U+202E>gpj, but I also confess to having no experience with sixth-level Unicode direction reversal rendering.
Anyhow, handing the entire RAR archive to VirusTotal produces the expected result:
VirusTotal – Product Pics malware file
It’s disconcerting to see ClamAV asleep at the switch on this one, but signature detection has become decreasingly relevant these days.
The Smell of Molten Projects in the Morning 