ryanrs posted:

Yeah, that's why you can't use SOOW rubber cord inside walls. Rubber deteriorates pretty quickly.

So what's a good 100-year insulation? I expect modern PVC will be cracked and brittle by then. Maybe PVDF?

PDP-1 posted:

At work we have a couple of rolls of teflon coated wire that are supposedly surplus from the Apollo program. The wire itself looks like it could have been made yesterday but the tin rolls it comes on are very obviously old and have 1960s-ish style design. One of our old engineers bought it at an auction then gave it to the lab before he retired and nobody has used it because nothing we work on is cool enough to warrant breaking into the moon wire stash.

I'm on vacation right now but if anyone cares remind me after the 15th and I'll post some pics when I get back.

Skinnymansbeerbelly posted:

I have some questions about the the SPS30, because I have never had to care about the supporting bits of an I2C circuit before. The datasheet says on p 16 to use 10kΩ pull-up resistors, but if the Adafruit module already has pull-ups on the bus, then they're not necessary, yea?

The S8 and SPS30 both spec 5V input while outputting 3.3V, so I guess I'm running everything off of the 5V. That Adafruit module says it can run off either 5 or 3.3, but I don't understand: will that work with it's level shifting circuitry if the I2C bus needs to stay 3.3V?

The Senseair sheet states on p 2 that it is unprotected against surges, do I need some sort of power conditioning, and if so, how? The manual for the power supply I'm looking at says overvoltage protection kicks in at 6.5V, which is more than the sensors specs. Also I hate that fake USB C power bullshit. Can I cut off the ends of a micro B power cord, crimp dupont connectors on and raw dog it?

kid sinister posted:

So you're saying I should be replacing my WW2-era radios with stuff from the space race?

ryanrs posted:

The Adafruit sensor can run on either 3.3V or 5V, but not with a split 5V supply / 3.3V I2C. If you feed the Adafruit module 5V supply, it's going to pull SCL and SDA to 5V through 10k resistors.

I suggest powering the Adafruit SHT40 with 3.3V from the S8's regulator output DVCC_out.

The built-in 10k resistors in the Adafruit module are sufficient to pull up the bus. You don't need to add more unless you're trying to run long wires or faster bus speeds.

I'm not exactly sure what you're asking re USB 5V, but the Senseair manual is just saying that if you plug it in backwards or to 12V, it's gonna kill it. Or if your power supply fails and somehow gives out 6.5V, that might kill it, too. IMO just hope your power supply doesn't fail.

Shame Boy posted:

My dad's getting into playing with Arduinos and wanted some recommendations on an Arduino C++ book to buy. He's an old EE who's very good at that side of things but in the past has always thought that getting everything set up and learning to program was "too complicated" so he'd just write all his microcontroller programs in assembly (because that's somehow less complicated to him). Now that Arduino has kinda made that entire thing trivial he's giving it another shot and wants a book to learn with, but I'm so far on the other side of that experience scale (what with being a professional code rear end in a top hat for nearly 15 years now) that I haven't really looked at programming books since college. Is there anything good out there, preferably aimed at my dad's somewhat unusual niche of already knowing the electronics side real well?

some kinda jackal posted:

I have a shower thought project that I'd like some advice on.

some kinda jackal posted:

I guess this is less an electronics theory question and more a "is there anything obvious I'm missing" question.

One Legged Ninja posted:

I was also going to suggest getting a replacement needle from an automotive instrument cluster instead of printing something, but then I looked some up, and they're more than a simple piece of plastic should ever cost.

kid sinister posted:

Got a local DIY salvage yard? They'd probably have the best price.

Ambrose Burnside posted:

A buddy of mine seems dead-set on loving around with high-voltage plasma stuff, low current (he says 20mA or less) but i'm pretty sure that's not of comfort to the human heart at 5k-20KV. using one of those purpose-made HV adjustable bench supplies. can anyone provide/recommend a concise safety guide or series of rules i can deliver to him, couple minutes talking or less, that is specifically tailored towards preventing him from dying in this endeavour. I know its a very bad idea but I can't articulate the harm reduction crash-course that will prevent him from ending up in series across his heart with the bench supply

Cojawfee posted:

Here's a nice rule: Don't. Direct him to some photos of what happens to people who mess up when they set up microwave transformers to do that wood art that looks like lightning bolts. 20mA is not low current when talking about putting 5000 volts across your body. If he still insists on doing it, make sure that he only touches it when the power is off and everything is deenergized. Even if he's careful, all it takes is one slip up when he turns it on and realizes he just needs to adjust something real quick and zap. I was messing with a CRT kit I was building and was careless when adjusting it and got a nice tingle in my hand and luckily it was only as bad as that.

ante posted:

Sagebrush posted:

20 milliamps at 5000 volts (1000 watts)

Cojawfee posted:

Here's a nice rule: Don't. Direct him to some photos of what happens to people who mess up when they set up microwave transformers to do that wood art that looks like lightning bolts. 20mA is not low current when talking about putting 5000 volts across your body. If he still insists on doing it, make sure that he only touches it when the power is off and everything is deenergized. Even if he's careful, all it takes is one slip up when he turns it on and realizes he just needs to adjust something real quick and zap. I was messing with a CRT kit I was building and was careless when adjusting it and got a nice tingle in my hand and luckily it was only as bad as that.

LimaBiker posted:

Let the guy start out with a TV flyback or a car ignition coil.

Both hurt like a motherfucker, and the voltage can be around 30kV. However, the current and power are more limited (think 1 to 4mA or so for the TV flyback, <10mA for the ignition coil). Few TV repairsmen have died from the 27kV supply, more died from hot chassis TVs that carry mains.

If he can play around with one of those for a year and not get shocked a single time, then he could consider getting a bigger transformer. If he does get zapped, he is not competent enough.

Either way, at the multi kV levels, things do not always categorize nicely anymore into 'conductor' and 'isolator'. Any bit of moisture in or on a surface can become a pathway for tracking, and continue to zap you.

The most important thing is to realize that it's all a lottery at those high power levels. Many people have survived it with just a little crater in their finger or hand. But he can easily be the one who gets 'stuck' onto the wire and can't release until his hand has burnt through, or never at all and die the worst death you can imagine.

Stack Machine posted:

Well, it's not an arduino book specifically, but a good place to start might be the second half (Ch. 11 and on in the 3rd edition) of Patt and Patel's textbook Introduction to Computing Systems. The first half of the book builds up from transistors to assembly language so your dad can safely skip that, but the second half is all of the foundation knowledge for programming in higher-level languages. My reasoning here is that there are plenty of arduino tutorials online, and both GCC and the Arduino API are very well documented, but the sort of person who prefers to program in assembly might be comforted by a more formal understanding of what the compiler does and how things like low-level library functions and device drivers are implemented.