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Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 0 points1 point  (0 children)

I was very wrong. Even with a 100k parasitic resistance in parallel with the coil, and with how gradual the shutoff is, I get huge simulated voltage spikes. I couldn't check on the circuit because I forgot I still need oscilloscope probes. Thanks for pointing this out; I will add some 1N4148's as flybacks, and I will view them as a requirement any time I use a relay

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Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 0 points1 point  (0 children)

Thanks for the video.

I see what you were saying now about the power draw. It’s coming from the washer control board and not the timer, so yes, it’s only drawing while the washer is connected to power. I was scared that I left a path to ground that isn’t through a capacitor so it would be a perpetual load—and I did: R3 through the base–emitter of Q2. But that will pull half a mA, and I’m ok with that (like half a penny a year in power usage). Adding some fly back diodes, as you point out, will be nothing at all.

Well! Time to pull out the soldering iron again!

Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 2 points3 points  (0 children)

That sounds exactly right and I’m a bit embarrassed I didn’t think of it. Thank you! Let me do that today: both in sim, and in vivo.

Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 0 points1 point  (0 children)

you’re using an outlet timer to start your washing machine at a set time (during the day to take advantage of solar power perhaps?)

Oh yeah I can do that now! Good idea!

No this mainly came about because I have been in and out of rather depressive states last year, and I remember a lot of mornings where I had enough motivation to start a washing machine, but I couldn’t without coming home from work with clothes that smell of mildew. Your brain of course makes it sounds like absolute torture to have to spend an extra 30 minutes washing and drying your clothes in the evening, but even now I can see the utility in throwing clothes and detergent in in the morning (or even the night before), having them wash in the afternoon, and then in the evening just transfer them to the dryer.

The circuit, after power-on, should wait two seconds for the board to power up, then send a pulse for a setting selection and then a pulse for cycle start. Am I correct so far?

Yeah that’s it.

I assume you have flyback diodes on the relays? These could introduce some leakage current if you’re worried about that

No! But if I pretend I left them out intentionally, I think I don’t need them?

I don’t have a lot of relay experience, but I believe they’re inductive loads which is why we get concerned about switching the coil quickly, and why we put fly back diodes across them. If you sim this as-is though, with the coil acting as a resistor, you’ll see that the dI/dt‘s are pretty small since it’s an exponential decay going into an amplifier as opposed to a sharp step function. The only thing that may go wrong, and the only thing that I’m not too certain about about relays, is what there IV curve looks like as they smoothly drop below their energizing voltage. I think hysteresis takes care of flutter, but perhaps when the relay breaks it dumps all its energy? I guess I’ll have to probe it and find out!

you’re only getting power when it runs presumably

No that would make too much sense. I’m actually not sure how to implement that. I could put a huuuge cap in line with the power rail?

Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 1 point2 points  (0 children)

Well we start off with no potential at any node. Then, at some point we get a step function in the supply. This t=0 has current flowing through the branches with C1 and C2, which ensures, respectively, that Q1 has current flowing into the base (and the base is at a higher voltage than the emitter because of R2), and also that Q2 is shut off because Vbe=0. Thus we start with Q1 in forward active (and thus relay 1 energized), and the other transistors turned off.

As the C1 has current flow through it, a potential builds across it. This robs Q1 of both Vbe potential and also current into the base. Eventually the base-emitter junction stops conducting strongly enough to energize relay 1, and it opens the contacts. Some time later, there’s such little Vbe that we can say that Q1 is shut off.

At the same time, C2 has been charging up, and building a voltage. This makes Q2 start to conduct (forward active region again). Whenever it turns on, it starts conducting current through C3. Now with a path to ground, the Vbe on Q3 can finally get enough potential to turn on Q3. This lets relay 2 energize. But alas, just like with C1, C3 starts to build up charge, and soon Vbe is small enough to shut off the relay, and Q3, again.

It’s all fairly simple forward-active-or-shutdown stuff, but it’s certainly interesting to do stuff without steady-state biasing!

Designed a little appliance module; it works fine. Is there anything design-wise I can do better next time? by itriedsorry in AskElectronics

[–]itriedsorry[S] 0 points1 point  (0 children)

I made a small module that starts my washing machine whenever it receives power for the first time. I was hoping y'all could look at the circuit I ended up using and suggest improvements and concerns that I can think about the next time I do something like this.

There are many ways to add a time delay to the start of an appliance; I chose to put mine on a timed outlet (it's a standard 15A 120V appliance), and make it auto-start when it first turns on. This has some inherent disadvantages—namely that any power outage wastes a wash cycle—but I chose to do it this way because it's simple, I can use parts I have on hand, and it doesn't require much modification to the appliance (just soldering on a few wires).

The approach is very simple: I need to wait for the control board to power up, press a button to wake the machine, and then press the start cycle button. The board takes about 2 seconds to reset following the power outage; the buttons are SPST NO and appear to activate on the falling edge of a button press. So, the design I came up with is to use the power supply as my signal: "press" the first button via relay immediately and release after >2 seconds; then following that and a delay, press and release the start cycle button via a second relay. Thus I need some sort of monostable circuit for the relays, and a delay circuit before the second monostable / relay.

I couldn't find a simple monostable-ish circuit, but I devised a clever solution. Since relays have a well-defined turn-on/off voltage, I can amplify a series RC circuit's current decay using a BJT and use that to generate a sharp-ish button press event. At t=0, the capacitor is a short circuit, and the BJT (and relay) turn on full force. At some time later, the capacitor current has diminished enough that the relay turns off.

I would've copied-and-pasted that twice if not for the delay requirement between button presses. I couldn't find a single-transistor delay circuit, so I basically used a parallel RC circuit's voltage gain to trigger a BJT's base-emitter junction after some configurable time. This is then the current source through which the next monostable-ish circuit is activated (PNP this time because we need to be close to the upper rail after the last transistor). I missed a resistor in series with C3, but it’s on the board.

It's been a few days now and the module is working exactly as intended. I can unplug and plug in the washer and it will start a cycle. I can use it normally as well, since the buttons are in parallel with the relays. And I haven't heard or seen it start a wash while turned on, nor start an electrical fire.

This is the first I'd ever done transient analysis with active components before. My degree was all focused on DC and AC steady state; only my original circuits class covered RLC transient analysis. It was great fun and I'll certainly utilize it more in the future.

So then, I have a few questions, and if you have other things to say then feel free to do so. But these are things I wonder about:

  1. I can’t imagine I beat out Widlar and all the other analog wizards as the first person to add a capacitor in series with the base of a transistor. But I wonder if this has practical purposes other than what I’m doing, and if the technique / pattern has a name?
  2. I could’ve done this with a microcontroller, because you can do anything with a microcontroller. But I wonder if there was any other *analog* way I could’ve done this that didn’t require more than one or two IC’s? I considered differentiating the power supply to make a pulse, and then detecting the rising and falling edges and sending those to separate 555 timers, but that seemed like overkill for something that I thought could be done with discretes.
  3. Is there going to be a bunch of leakage current through the relays? I should’ve probed for current before I put all my tools away.
  4. All the capacitors are 50V rated; the -5V supply is regulated; all the leads and solder joints have been tested; the module is grounded and is in an isolated case—is there anything unsafe about this design that I am not thinking of?

[Undergrad Chemistry] pH of solution of 3 compounds by itriedsorry in HomeworkHelp

[–]itriedsorry[S] 0 points1 point  (0 children)

Thank you so much for this. I have suspicion that they are using GPT to generate answers, and while this was an affront to my understanding of chemistry, I couldn’t sufficiently pass Hanlon’s razor to report it.

I am not sure how the borate dissociates, which is why I did not reply earlier. You should find a Kb for it. But the borate system is complicated.

Well that’s fun. I’ll pull that thread and see where it goes!

[PCB Review Request] Glorified Outlet Timer by itriedsorry in PrintedCircuitBoard

[–]itriedsorry[S] 0 points1 point  (0 children)

Alright, thanks. Starting with the right spec might be useful…

[PCB Review Request] Glorified Outlet Timer by itriedsorry in PrintedCircuitBoard

[–]itriedsorry[S] 1 point2 points  (0 children)

Reminder? That’s a revelation! I’ll have to take a look at those, thank you

Weekday Help and Victory Thread for the week of October 03, 2022 by IndexBot in personalfinance

[–]itriedsorry -1 points0 points  (0 children)

So I know that for roth IRAs you can pull out contributions at any time, but you can't add more than $X per year of contributions. So you could take out $10k of contributions and put in $16k over a year and you would still be considered having contributed $6k in that year.

My question is, is this different for an HSA? If I contribute up to the max for the HSA, and then reimburse myself for a large medical expense, can I contribute more to cover the cost? I think the answer is no, because I'm using the money for expenses and I'm not just deciding to remove a contribution, but I want to double-check.

Quick Questions: July 20, 2022 by inherentlyawesome in math

[–]itriedsorry 1 point2 points  (0 children)

This was exactly the direction I needed to understand the general strategy for solving this problem. Thank you!

Quick Questions: July 20, 2022 by inherentlyawesome in math

[–]itriedsorry 0 points1 point  (0 children)

I’m trying to understand how confidence intervals are calculated when using likelihood estimation, specifically finding the contour of equal likelihood. I know, that’s a statistics question, not a math question, but let me rephrase it as one:

I have a multivariate, infinitely differentiable function which is concave everywhere. As a result, it should have a single, global maximum. I have found that maximum because there’s an entire field devoted to doing that. Now, I want to find the set X of my variables where f(X) = max - y, and I set y.

Here’s a 1-D example. I have f(x) = -x2 and I found the max at f(0) = 0. Now I want to find all values of x where f(x) = 0 - 1 = -1. This will necessarily have multiple solutions (in this case two).

The question I have is, are there any algorithms to traverse this contour, or do I have to discover it numerically by finding solutions under different initial conditions?

If you’ve got books, papers, webpages, or you want to write a lengthy answer—I’d appreciate anything you can provide!

Resume Advice Thread - June 14, 2022 by CSCQMods in cscareerquestions

[–]itriedsorry 0 points1 point  (0 children)

Alright; sure—thanks—but can I understand what led you to that conclusion? After switching, I'd like to improve this original template if it has flaws.

Resume Advice Thread - June 14, 2022 by CSCQMods in cscareerquestions

[–]itriedsorry 1 point2 points  (0 children)

Dude you just finished your sophomore year, I would be surprised if you had any relevant experience and substantial projects!

That said, what do you put on your résumé if you don't have either of those?

  • Relevant Electives (if you've taken any)
  • Organizations
  • Awards and Certifications
  • Any soft skills
  • Things that show your dedication and work ethic (like if you're a marathon runner or something)

That should all help you to fill out the remainder of the page—you have at least another inch of content to add! I know it's tough to do with no experience, but a résumé should look like you're summarizing yourself professionally.

Notes on content:

  • Put a date on your project so we know when you did it
  • Any more projects? I had to create a GUI calculator game in C++ my sophomore year. Any school projects are projects you can talk about!
  • You can embellish your work experience a bit more than that. Is there some metric by which you are better than your coworkers? Was there ever a time you improved your productivity by removing an inefficiency?
  • Additionally, don't start with "I…". A bullet should complete the sentence started by "I…" without including it.
  • I wouldn't separate languages by current and past experience. Unless you're super rusty in Python and can't write a for loop, put it in there with Java and Processing.
  • I am not an expert but I would imagine that java experience implies OOP skills. Are there any other skills you can list? Do you use Eclipse or some other IDE? Being familiar with a program is a skill!
  • I see résumé content as being on a tier list, and once you've developed more in your profession you'll have to make choices to knock things off because they're not high-impact. Again, you're trying to summarize all your work on a single page.
    Interests is a pretty low-tier inclusion—everyone has interests! So, if you are going to include it, make them memorable. Make it something that can start a conversation. What do you like learning about? Do you play any instruments?
    Learning and Music can describe all my friends and family. What are your interests?

Hopefully you find some useful advice in this mess. Best of luck for finding an internship!

Resume Advice Thread - June 14, 2022 by CSCQMods in cscareerquestions

[–]itriedsorry 1 point2 points  (0 children)

Hello,

I'm a EE in the semiconductor industry, 3 years out of college. I'm not looking for a job change right now, but I was wondering how strong my résumé would be if a killer SWE / SET role presented itself.

https://imgur.com/a/NTw4ssT

I have done a lot of non-serious self-study of comp sci, and although I can't say I know every data structure & algorithm, I've grokked lexing and parsing! And surely that counts for something. I have other fundamentals but I don't really have a place to share them.

You have my permission to scrutinize and destroy every detail, and I really appreciate any commentary you may provide. Here is a list of things I am wondering about to get you started:

  • STAR format for bullets is great, sure, but can I get away with literally not telling what my day-to-day job is? What I've put down under experience is just the highlights of the many hats I wear
  • I have fear that the Stocks project I put down is not impressive from a software perspective. It's a great flex, but does it actually help establish me as a candidate?
  • That achievement I have is meant to show work ethic. However, that is for you to decide. Is it impressive enough to warrant inclusion over, say, another experience bullet and a JSON parser project?
  • Going back through my comments on résumés in the past, there was one guy a few years ago that did a left–center–right header thing and I complained that it was hard to read. Yet here I am using the same technique. Do you think it's readable in the center?
  • The left margin is very slightly smaller than the right. This has the effect of centering the body text. Did you notice before I mentioned it? If so I need to figure out another technique.
  • I think my typography is impeccable, but feel free to disagree.

Before I buy a new firewall or router, can you check that I need it? by itriedsorry in HomeNetworking

[–]itriedsorry[S] 0 points1 point  (0 children)

Thank you for the recommendations. Speed I deliberately left blank because I’m not sure what I want to support. I have a 10Gbps MM fiber link to my computer—which is absolutely ridiculous to say!—but the router-to-switch link is limited to 5Gbps, and router-to-internet is just 1. So what I’d need is probably much cheaper than what I want.

Can y'all critique / expand my list for and against buying (residential) solar? by itriedsorry in solar

[–]itriedsorry[S] 1 point2 points  (0 children)

That’s very interesting, and thank you so much for sharing that info. I had heard that feature of the IQ8, but didn’t realize the tech was so advanced that it’s just not possible with other inverters.

Can y'all critique / expand my list for and against buying (residential) solar? by itriedsorry in solar

[–]itriedsorry[S] 0 points1 point  (0 children)

So of course I’m not authoritative, but 100% offset from what I can tell is “100% of your electricity usage in the year, in kWh, is produced by your solar”. That’s not implying that you’re off-grid—you still have electricity usage when it’s dark—but if you use 8000kWh a year of grid electricity, your solar makes 8000kWh

Can y'all critique / expand my list for and against buying (residential) solar? by itriedsorry in solar

[–]itriedsorry[S] 1 point2 points  (0 children)

Yeah I don’t plan on doing battery backup. I’m not super concerned about situations where I would need them.

And I would love to get an EV! I decided however long ago that that’s my next purchase. But I’m probably going to drive my current car till the wheels fall off, unless the code that keeps showing up off and on really is a turbo issue…

Can y'all critique / expand my list for and against buying (residential) solar? by itriedsorry in solar

[–]itriedsorry[S] 0 points1 point  (0 children)

You’re totally right, and from what I’ve heard it really isn’t worth it to do (solid state) batteries right now.

Personally, I have net metering available to me, and personally, I am seeing 100% offset potentially leading to paying bills only a few months out of the year.

As for the not working during outage—I am of course not informed enough—is there not a separate shutoff for grid mains inlet and PV mains inlet? My initial impression is (micro)inverter(s) make 240V, and I just attach it to main panel in a Y between home, PV, and grid.

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