Electrical Engineering

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jippie

07:34

morning

7 hours later…

Niall C.

14:57

Hello all. I've got a "waterproofing electronics" question on Home Improvement. Would it be on-topic on EE?

Q: How best to waterproof a small electronic device?

I have a small electronic device that's dimensions are roughly the size of 2 poker chips stacked on each other. It's powered by a watch battery that needs to be replaced after a few months and sends out a wireless signal. I'm trying to find a waterproofing solution for this device that I can tak...

waterproofing

2 hours later…

W5VO

16:29

@NiallC. Eh, not really

rakesh

16:40

HI, could some1 tell whether .mif file is supported by mentor graphics ?

W5VO

@rakesh that's a really vague question

rakesh

oh sorry, ..

W5VO

heh... do you know how many different software packages they make?

you're probably better off finding the user manual

rakesh

i want to initilize my RAM with some data.. so i decided to read it from a file. certain tools support certian file types. like quartus supports .mif file. i am using model sim and precision synthesis . so i want to know what type of file i should have to initialze my ram

i write in vhdl

W5VO

@rakesh did you try googling "Modelsim initialize ram"?

rakesh

16:53

thanks .. i didn't try exactly with these words..

Niall C.

17:15

@W5VO Fair enough. I'll leave it where it is. Thanks.

jippie

17:41

Anyone know how I can measure current in circuit lab?

in time domain analysis

The Photon

18:00

@jippie I tried to do it when looking at a question the other day but couldn't figure it out. Only spent a couple minutes on it, though.

jippie

@ThePhoton I found it, you can click on a component's node. Then it adds voltage and current for the component,

trying to snubber a simulation, but I'm not really happy with the result

guess I have to install full blown spice

I'm trying to wrap my head around what the underlying design criteria for an RC snubber network should be

jippie

18:31

Let's just ban inductors from power electronics, that simplifies things a lot.

The Photon

@jippie For certain interpretations of "simplifies".

jippie

at least we don't need snubbers

Why not use a gas discharge device to limit the voltage across the swithc?

W5VO

19:17

@jippie Snubber design is basically finding the right "ballpark" and then using trial and error.

jippie

@W5VO there must be better rules of thumb than mine,or at least more.

@W5VO you make electronics (and snubber networks in particular) sound like black magic

MLM

19:43

Do you think a 5/16"(.3125") rod could fit well with a 8mm(.314961) bearing?

I am thinking of getting rod from a hardware store which only has imperial stuff (atleast for rods).

The Photon

Engineering fit

Fit refers to the mating of two mechanical components. Manufactured parts are very frequently required to mate with one another. They may be designed to slide freely against one another or they may be designed to bind together to form a single unit. The most common fit found in the machine shop is that of a shaft in a hole. There are three general categories of fits: 1) Clearance fits for when it may be desirable for the shaft to rotate or slide freely within the hole, this is usually referred to as a "sliding fit." 2) Interference fits for when it is desirable for the shaft to be secure...

MLM

A press fit to be more precise

W5VO

@jippie It's difficult to accurately simulate and estimate what's really happening in your system - so following guidelines and general rules of thumb will get you close

The Photon

@MLM According to another thing I found, you are too loose for a press fit.

More like an "RC7" sliding fit.

kanabco.com/vms/eng_mhandbook/eng_mhandbook_08.html

You have about 0.003 clearance on a size of 0.3",

jippie

@W5VO I'm trying to figure out the guidelines; actually trying to find them first

W5VO

19:53

@jippie I've got a few papers, give me a sec

jippie

@ThePhoton are these rods actually manufactured to .003 precision?

MLM

@ThePhoton RC7 says "precise guiding of shafts" I wonder if this is good enough to not bind with a linear bearing block like:

W5VO

@jippie newark.com/pdfs/techarticles/cornell/design.pdf

The Photon

@jippie Good point

W5VO

That should get you pretty close

jippie

19:54

@ThePhoton question

The Photon

@jippie Which makes the point that @mlm oughta check on that.

W5VO

@jippie space.dianyuan.com/blog/u/50/1170381240.pdf Here's another, but I don't like it as much

jippie

@W5VO thnx. I'll have a look at it

@W5VO yeah it is much slower to load

the first document seems to answer couple of my questions, at least that what it looks like while scanning it

W5VO

The first one is good because it has a few "quick and dirty" recommendations to get you in the ballpark, and enough advanced analysis to hang yourself later

jippie

@W5VO thnx, I appreciate it.

MLM

20:03

@ThePhoton Not sure on that one. The online ones I am looking at say: precision g6 h6 (looking it up). But I guarantee the hardware store (Menards will be different). Assume some tolerance. I am also looking for a rule of thumb on that

jippie

any links on AC RC snubbers too perhaps @W5VO?

MLM

I am looking at this pdf and I gather that a g6 h6 is a clearance fit for what I assume is the stated value.

But take that with a grain of salt as I do not plan to buy online

@ThePhoton Thanks for the "fit" links

The Photon

@MLM NP

W5VO

20:24

@jippie Sorry, that's what I have. In theory it should be similar

the impedance of your load is ideally constant