Our theatrical lighting instructor in college told us a story of an overnight auto commercial shoot he worked. They had generators to run the huge lights they needed for the camera work, and there was all this surplus cable lying around. Some intern decided it was a tripping hazard and coiled it all up around a fire hydrant, basically turning the cast-iron water mains throughout the downtown city neighborhood into an electromagnet. Apparently lights were flickering in all the buildings for blocks around the shoot location when they fired up the generators.
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Very handy information to have… Will have to file that away…
The way EMI works, the current generated is proportional to the area of a loop. It is the area of the loop times the strength of the field.
Looping twice doubles the area. Looping one way, but then looping back the other way cancels out the first loop.
So a twisted pair of wires (like an ethernet twisted pair) are lots of little loops, but every other one is going in the other direction. +1, -1, +1, -1, etc. If you instead just had a positive on one cable and a negative on the other, if the loop they created could be a significant area.
If you loop the entire ethernet cable in a big spool, like a 12in spool, then both the positive and the negative are both spooled in the same way, so it will again cancel out, and you won’t have any current generated between that positive and negative. However, if you have those in a loop, and another cable not in the same loop, then the EMI will try to generate current through the positive/negative through the other loop (like a ground).
You can really hype yourself up about all of this though. A UART signal, for example, which is digital, and very little current (high impedance) can be susceptible to this. If and extra 1mA goes through a stepper wire, who cares? If 1mA goes through a UART, it might actually increase the voltage by 3V, and cause a 0 to look like a 1. This is why the LCD wires are susceptible to noise, and the motors aren’t.
The endstops are sort of in between, because when they are open, they are not a loop, so they can’t catch much EMI. When they are closed, they do catch some current. But the signal is being pulled up and the ground is at ground, so there is already some current moving through the endstop all the time, so a little more or less isn’t a huge deal. But it is a lot less current than a motor, so they are in between.
Another example is the CAN interface, which is used in cars and trucks to transmit digital signals in close to the noisiest environment there is. It always moves significant current from end to end, and the “idle” voltage is 2.5V. When something wants to send a 1, it pulls one wire to gnd and one to 5V. When it wants to send a 0, it pulls the first wire to 5V and the second to 0V. This keeps enough current going through the wire that 1mA won’t be the difference between a 1 and a 0. Some of that is also to manage multiple cpus trying to send messages at the same time.
It is all super interesting, but things that an RF engineer says are “Really Important” probably aren’t to someone working with A/C lights, or DC motors.
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I should also mention that the loops also generate EMI in the same way, so a loop of + and - power cables will create a lot of EMI too.
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I’ve Klein tool. A heavy-duty professional wire stripping tool that you can also use for shearing.
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What solder iron or station do you all use?
I got mine from amazon a few years ago, and it looks like it is no longer available. But I found it at walmart:
I posted it somewhere else, but I think the solder is something to pay close attention to. Maybe more than the iron. The iron should have temperature control and replaceable tips. Fine solder makes a huge difference. There are also some cheap tools, like tweezers and a solder sucker that help a lot. I have a knockoff panavise, amd I almost never use it.
If you get into very small stuff (surface mount parts) then magnification is really helpful. I am always shocked at how bad my soldering looks under a microscope if I soldered it with the naked eye. I am also surprised at how much more control I have over my hands when I can see better. My eyesight is generally 20/20.
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I wish I had found this video sooner. I wasted literally the entire supply of female connectors trying to get a proper method worked out. Now I put them in the slot one size too big, crimp that so it can fit in the correct one, then put it in the correct slot, squeeze four clicks (the second to last before it fully crimps) and slide the wire in and crimp that but I still have to flip it over and do it upside down for it to slide into the housing. I also had to loosen the strength on the crimper too by 1-2 notches Those cheap crimpers don’t come with any instructions and it was way more involved than a noob like me would have guessed.
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