asdf32 posted:

Random question, what do people use for calculators, graphs and especially algebraic solvers?

I just discovered Microsoft Mathematics and it's fantastic. But given that its years old I'm now wondering what else I've been missing. I've also long used wolfram alpha, but it can sometimes be hit or miss in terms of its willingness to solve your problem (and it's not super fast), though it's still the most complete solver I've found (it does laplace transforms and inverse laplace transforms and has many circuit tools etc). Is there anything else out there?

Mathmatics lets you leave things in symbolic form and do most of the manipulation that way. For example I started with a circuit and used it to simplify the S domain transfer function and find the roots all in symbolic form. A neat detail is that 'C1' is treated as C subscript 1 (as you can see in the picture) which is really well suited for circuits. At any point you can assign numeric values to C1 and re-evaluate to simplify or find the numeric solution. Or you can assign a symbolic expression to a variable as well, such as z1:=1/(s*c1).

Although it appears to run out of steam when you hit complex numbers. Although you can substitute s:=wi and i is seen as complex, it appears that it can't continue to find symbolic solutions in most cases when an i is involved. So I can't get the full symbolic representation of the gain/phase plots out of the transfer function.

Aurium posted:

I wouldn't bother, outside of analog signals in a very noisy environment (like audio when you hear stuff). It's slightly harder to work with/bulkier.

Grounding the wrap improves it's shielding immensely.

It'd be fine to connect it to the table.

Aurium posted:

I can't tell you it definitely won't be an issue.

Digital typically doesn't need shielding until you get long runs or high speeds. It's also typically low current and doesn't generate much noise.

It won't hurt, it will add fiddlyness. My suspicion is that you won't need it, I can't really give any other pointers.

Aurium posted:

In many cables there's also a bare wire woven into the foil that you can solder to. Here's an example that someone in the CNC thread linked earlier. This is the easiest best way to do it.

Many connectors crimp to shielding in addition to being connected to the internal wires. This is nice for production, not so much for prototyping unless you already know tons of connectors in all their sizes, as well as having the appropriate crimpers.

After that, your other ideas would be fine.

Zuph posted:

You can buy solder sleeves with a lead-wire attached. Slip it over the insulation, hit it with a heat gun until the solder melts, and you've got a good ground connection.

http://www.digikey.com/products/en/...d=0&pageSize=25

Murgos posted:

Are all the parts connected to the same power and ground? Also are you using single ended or differential signaling?

huhu posted:

Does anyone have experience seeking out a cheap-ish PCB manufacturer that's RoHS compliant? I currently have 10cm*10cm boards that I'm getting made for ~$2 each but they can't guarantee it's RoHS compliant so now I'm looking elsewhere.

Methylethylaldehyde posted:

Ok goons, I have a need for a ~36 volt power supply for a project, and I have two ways of doing it. One would be to get three 12V lead acid batteries in series and schlepping around 50 pounds of battery, the other choice is to do something like this to a Dewalt 40v battery pack. I'm leaning more toward the battery pack mod, just because eventually this project is going to need to be something you can easily carry.


On a scale of 'UL certified' to 'aboveground pool in the basement' how stupid is this mod?

Zero VGS posted:

I found some affordable 12v reversing fans I was searching for in an earlier post:

https://www.amazon.com/gp/product/B01MV5S321

Now, they come with a two-wire switch circuit shown here:



If I click in the switch, the fan stops then reverses direction; if I click it again reverts to the normal direction.

So I need to figure out:

1) A circuit or a cheap off-the-shelf component to make a fan alternate between intake and exhaust every 60 seconds, looping forever.

2) An RF transmitting/receiving circuit so all the other fans are synchronized to what the primary fan is doing.

Any ideas on where I should be looking? Thanks for the help.

Malcolm XML posted:

So my house lights use an unencrypted u authenticated protocol to set dim levels

If I change house number to, say 10, I gently caress with my neighbors


They came with the house and are wired in with 433.92 MHz wireless controllers, and are considered pretty high end which means the wall switches cost 125 earth dollars to replace

Cyril Sneer posted:

Okay fun RF question that's been bugging me. See the following image:

http://imgur.com/a/qHPjn

I have a parallel plate capacitor driven at some frequency. Between the plates there are three thin conductors with the electrical lengths shown (consider these as three different scenarios - the conductors don't actually "see" each other). Assume the plates of the capacitor are far away from the conductors and the field is uniform.

Question: what is the current distribution along each of the conductors?

This is really tripping me up for some reason. Typically, the boundary condition imposed is that the current goes to zero at the end points. So, for example, for the quarter-wavelength conductor, that would mean you have two current nodes. But, as its a quarter-wavelength, it "should" have a node at one end and anti-node at the other. Basically, I'm having trouble squaring these two assumptions about the physics of the situation. Any help here would be most appreciated!

Brekelefuw posted:

I am etching brass/bronze/nickel silver using a 30V 10A adjustable DC power supply but I can't seem to get the amps anywhere near what people talk about using when they etch.

When I etch nickel silver, I etch at 15-20V and I get about .100-.200A.

When I etch brass or bronze at the same voltage I get roughly .040A and then it quickly drops to 0 and stops etching.
I can't for the life of my figure out why this happens, or how to get the amperage higher. I have the knobs for the power supply on full amperage.

I am using salt water with hydrogen peroxide as the electrolyte which is what most people use. I connect the positive lead to the workpiece, and the negative one to the handpiece that has an electrolyte soaked rag on it, the same way they do with professional marking machines.

Typically in tutorials, people talk about using anywhere from 2-24v with a 10A battery/car charger/power supply.


PS. With 15-24V at lets say 1A, will I die?

Acid Reflux posted:

It actually does a pretty admirable job of protecting the surrounding components from stray solder bits and excessive direct heat, as long as you don't just mash the iron into it or point the air nozzle at it for long periods. It's also great for preventing the inevitable "oops" when you slip and smack your hot iron tip into an unidentifiable (and now missing) 0201 resistor or something.

Zero VGS posted:

eBay and such have a lot of off-the-shelf voltage regulators that step up/down from 5/24/36 volts to 12v and such, but i was wondering if anyone knew of an affordable, high-wattage (200-400w) voltage regulator that would take around 10-14v and bring it to exactly 12.0v ?

Trabant posted:

I think the answer is "eBay/AliExpress/disassemble a used monitor" but thought I'd ask:

I'm going down the path of making a briefcase to hold my Amiga emulator, a la this, because I'm a massive nostalgia dork. I need a display module that will ideally handle an HDMI input since that's the only signal my emulator device outputs, which in turn means I need a way to bring the audio signal out from the display to a pair of small speakers. Given that I'll be using it exclusively for Amiga game emulation, I'm not looking for some high-performance display and have zero need for touchscreen capabilities.

This guy would work well since it does HDMI and includes audio out, but it seems overpriced. Plus, I'd prefer something in the 13-15" range, which makes me think that my options are:

1) Cannibalize an old monitor which has either integrated speakers or (better yet) audio out
2) Try my luck with AliExpress items like this (which I know includes audio out because it's shown with speakers but has a massive bezel) or this (which should/might) or build-my-own combo of control board and display.

Is there an option I'm overlooking, or some parts source I just haven't thought of?

Thanks!

late edit: seller "oupin6" on eBay is probably the best single source I've found so far, e.g. this and many other items. Little confused by his warning though -- I have no idea how to parse this:

Stabby McDamage posted:

How do these work? These cables look passive, but isn't HDMI entirely digital?

RedChesterfield posted:

I'm super loving green when it comes to wires and burns, but here goes. I want to use some spare pc case fans I've got kicking around for a non-pc project.

These are some lovely 12v 160mA fans I've got on hand. So, am I hosed in my understanding, or can I just find a 12v 1A power supply from my local pawn shop bin and splice/solder/knot a pair of these fans to that? In parallel to the salvaged plug so they get equal voltage? Am I going to burn down my house?

peepsalot posted:

Yeah if you wire them all in parallel, then as long as you supply the correct voltage, and your power supply is capable of outputting at least the sum of the load currents, it will work.

johnnyonetime posted:

Will this be safe or will I end up with a high altitude fireball?

johnnyonetime posted:

I've got big dessicant packs from work? I might put one or two in there for good measure. I'm doing this in Colorado and the relative humidity here is usually low but again, didn't think about that.

TotalLossBrain posted:

It's possible that the router had a protective device on the input, like a metal oxide varistor. Those can be replaced or just be removed. But I'm not sure this type of protection is legally required in consumer level devices.

Edit:. However, as the poster above me points out, chances are high that other stuff fried even if there was a working protective device

kid sinister posted:

I always thought the toilet paper tube method of storing cables to be very clever. Doesn't work too well horizontally though.

I'd just go to the hardware store and get a couple plastic containers. See which size fits your shelves best, then buy a dozen and return the rest.

edit: and get some flat boxes with adjustable dividers for the really small stuff, like fishing tackle trays.

Ambrose Burnside posted:

Fender Anarchist posted:

I've got a stereo receiver (JVC RX 318) that's got fucky audio in both left channels. I'm suspecting a bad cap, but beyond that i have no idea what to look at; the board is some multilayer thing and i can't travel circuits to see where the traces from the speaker plugs go to. Is there a trusted repository of service manuals somewhere out there?

insta posted:

If you have stranded wire, use ferrules. They're neato.

sharkytm posted:

I've had good luck with the cheap Chinese 4-jaw crimper for ferrules.

babyeatingpsychopath posted:

I need to get a good deal on one of those. (The AF-8, AFM-8, HX-4). I recently found out the AF-8 can crimp coax pins; no more soldering!

babyeatingpsychopath posted:

We've got the crimpers at work, but when there are three people crimping on two different projects on opposite ends of the shop, it gets to suck. Having an AFM8 of my own would be choice. That and whatever that environmental splice crimper is (for M81824/1-xx splices). I wonder if there's an HX-4 die...

fake edit: oh snap there is! Hmmm, might have to invest in one of these.

Hypnolobster posted:

So, I want to switch a 30a, 110v normally open contactor with microswitches. Any single switch turns on the contactor, and they all have to be open to turn it off.

I'm assuming I could have a 12VDC system of several microswitches wired to a pair of busses, using a DC control/AC switch SSR to switch the coil side of a normal industrial contactor, right?


e: drawing at a 2nd grade level for some relative clarity

Hypnolobster posted:

Followup, if I'm running the DC control wire a significant difference (like 50 feet), do I need to think about voltage drop/load on the DC side of the SSR? It's hard to find a spec for that, but I'm assuming that I could pretty easily use 20 gauge wire for the microswitches and just run the DC side at 24v or so and not have any problem.

Malcolm XML posted:

has anyone made a usb-pd based power supply

Dominoes posted:

I need to evaluate if this is more dangerous than I thought to both life and the electronics. Ie quick googling shows that wet environments or unlucky factors could turn 24v DC deadly. Don't have a good grasp of how parallel-chaining these lights (which alone don't use that much current) would affect things, and affect the wiring/relay/AC adapter reqs.

Dominoes posted:

Got another one. Do y'all have any advice on what relays to buy for controlling relatively low (<2amp) currents? I've read several guides on solid state vs mechanical. From what I gather, either will work for my purpose (relatively infrequent switching), although solid state may be more reliable over time due to fewer moving parts. Should I just pick an arbitrary cheap SSR with the right current max? How many feet should the SSR have? They seem to come in many varieties.

I'm using standalone boards off amazon that have the circuitry needed to plug directly into a signal line. However, they make loud clicks when actuating. I was planning on putting relays on the main board, but from what I find on Digikey and elsewhere, they're about the same price as the full relay modules off amazon, and it's not clear how I'd wire them. (Although I've found some guides). Ie: SSRs on Digikey. Mech relays on Digikey.
Relay board on Amazon. 8-relay full board for the price of 2 digikey relays. Could probably just use these instead of designing a custom one.

Dominoes posted:

Peristaltic and submersible pumps. ~1/2 A. (And those daisy-chain lights which I'm dodging for now)

Ambrose Burnside posted:

something like a simple green-type gentle degreaser work as a substitute? I've had a nose out for IPA at the grocery store/pharmacy for weeks and havent been able to snag a single bottle

babyeatingpsychopath posted:

I came here to post https://www.youtube.com/watch?v=vq968AFgPhg, which I got from Hackaday today.

taqueso posted:

Free 130nm chip fab service for your open source design
https://fossi-foundation.org/2020/06/30/skywater-pdk
https://github.com/google/skywater-pdk
I'm going to make the 666 timer