Morning all.....

@NathanOsman I'm at starting level of studies, I want to know one thing in you circuit.

@KrishnShweta Yes?

As you said you want to split that into eight wires, I want to where you will connect it?

I mean from where you will split?

The wire is hot from a wall socket. It connects to eight relays. I need to know how best to connect them together.

OK OK....

@NathanOsman what gauge are the wires, and what sort of box are they inside?

Let me check for you quickly here...

Looks like 18 gauge.

It connects to the wall with one of these:

(Not exactly that model but one similar.)

so all 8 wires are going into that one plug?

Well, not in the plug.

Here's a really really crude drawing of what I'm trying to do.

The wire coming from the outlet needs to split so that it can connect to the eight channels.

righty-o

Forgive my truly awful drawing skills :D

other than the fact your black and white wires in the diagram are backwards -- always switch the hot, never the neutral!

what sort of box is this being enclosed in?

I know, I realized after I drew it that I had the wires mixed up.

@Shalvenay Well, I know this isn't going to impress anyone, but the whole thing was going into a cardboard box.

All of the exposed wire should be where it connects to the relay.

@NathanOsman ugh. can you get a better box, something with a UL 94 rating?

I'm open to suggestions :) I want to do this safely.

(if nothing else, a fiberglass junction box of the type used for electrical work + a matching cover plate could be used?)

Out of curiosity, what is the potential hazard of cardboard?

@NathanOsman sparks + cardboard = fire

/facepalm

Of course.

I was thinking "cardboard is not conductive, what could go wrong?"

Yes, that makes sense.

Would a wooden enclosure work? Perhaps plywood?

are there any other leads from this gadget (relayboard + controller + wiring) to the outside world?

@NathanOsman wood's a bit of a pain in the arse for electrical chassis at small sizes.

@Shalvenay Well, the other side of the relay connects to a microcontroller but it's optically isolated and 50 mA / 5V DC.

@Shalvenay Ah.

@NathanOsman right, good that it's optoisolated -- is there anything else that connects to the microcontroller board besides its own power supply?

Just a WiFi chip.

cool. no buttons for the user to push I take it?

And it's bus-powered.

@Shalvenay No, it is controlled via WiFi.

right...so it's powered off a USB power supply?

Well, it's a Raspberry Pi. I've got it powered by a USB hub that is connected to the wall with its own adapter.

@NathanOsman can you take the USB hub out of the picture and wire an AC adapter directly to the RasPi?

(well, not a typical boxed AC adapter...)

I haven't been able to find one that could supply enough current. It needs 2-3A.

Most of the adapters I have laying around are 500 mA or 1A.

Here's another (really terribly crude) drawing.

The USB hub connects to the wall.

Both the WiFi chip and the Pi itself connect to the front of the hub to draw power.

ah, why not bus power the wifi chip from the pi?

It draws too much power.

ah, arrgh.

I know, it took me a while to figure that out.

It sort-of worked but it would cut out every so often.

The hub provides 3A total.

...which is enough for the Pi and WiFi chip.

The red wires connect to the relay.

the problem becomes cramming this all into a box :/

Thankfully none of this is very big.

@NathanOsman relative to typical electronics packaging, the hub and the power supply are the worst problems -- mainly because their connectors impose a ton of chunkiness

can you replace the hub with a smaller one?

It was hard finding one that put out 3A to begin with :P

I honestly don't care if the box ends up being a little large.

I might eventually want to add more relays.

true

does this actually all have to be wrapped up into a neat-ish package, or are you OK with the power supply living outside the box?

Sure, it can be outside the box.

That's fine.

or actually, NVM I think

It doesn't have to look pretty :)

get a pile of these: homedepot.com/p/…

What are those?

cable clamps -- they allow you to get all those power cords out of the box without snagging or otherwise damaging them

homedepot.com/p/…

that box should be plenty of space

(they have smaller ones too if that's too big)

Okay, cool.

Thanks for the advice.

you should be able to get the appropriate size bit for putting 1/2" conduit KOs in that box while you're at it

What should I use for connecting the wires, though?

and as to the actual wire connectors? Wago type box connectors like homedepot.com/p/… are your best bet (better than wirenuts even)

well, let me double check that

yep, go for it

those connectors will work grand

So how exactly do those work? (I've never seen one before.)

you'll need 2 of them per, spliced with 18AWG appliance wire jumpers between the two (you can get that at the orange borg too)

@NathanOsman strip end of wire, (twist together if you're dealing with stranded stuff), stick in hole in connector, repeat for other wires/holes

they're designed to be wirenut-substitutes

That easy?

yep

Cool!

I was looking at using a terminal block before, this sounds much better.

(electricians don't have time to be fussing around for 5 minutes making 1 connection :P)

ya, it's way better

Thanks for the assistance.

as to the power supply? stick a field-mount receptacle on a length of cord material....

something like this: homedepot.com/p/…

and have that inside the box, wired up to the mains junctions

Sorry, I got a bit confused. That's a female receptacle. Don't I need to a male connector to plug into the wall?

this is for plugging the power supply into :)

and then you wire it to the mains junction points, which get wired out through another length of cord to the wall-plug

as to the cord to plug into the wall: homedepot.com/p/…

Organic, Free-Range, Gluten-Free LEDs

Out of curiosity, why wouldn't I plug the adapter into the wall and have its other end run into the box and connect to the equipment?

Is that bad?

@NathanOsman it's not nearly as neat a package, and also the adapter's secondary side could get accidentally crossed to mains

Ah, okay.

I'm glad I got started on this project early. It's going to take a while to get everything together :D

(also, you can get some decora-style duplex receptacles and make decora-shaped holes in the front of your NEMA box, and mount them to your box -- or you can have your box be a cable-squid, whichever you prefer -- as long as things that put mains out are all sockets like the receptacle I linked for plugging the power supply in inside the box, you're good :)

That's exactly what I had planned.

Should be good to go then.

yeah, glad I was able to help :)

I will try to remember to write this up on my blog when it's all finished.

@NathanOsman All the best... :-)

Is anyone here

nope

These electric mosquito squatters are not really a pleasant feeling

Try TV deflection

They leave these nasty brown marks on my arm

I hate their sounds...

I always snuggle them to sleep

Question

The smallest drill bit I have is 5/64 of an inch and it seems way too big

@R_Misra You can buy a smaller drill bit. Actually I've seen used bits from PCB shops being re-sold as surplus.

You may also need a smaller drill chuck or pin vise to hold the smallest bits.

What size drill bit is usually used for through hole stuff?

@R_Misra In a pro design, you size each hole according to the pin that will go through it. Maybe 5 to 20 mil (0.1 to 0.4 mm) bigger than the diameter of the pin.

Perfect. Thanks!

Dremel with precision chuck + 1/8" shaft standard rills I manage to make holes as small as 0.15mm with relative ease on my revised and upgraded dremel holder

can parts designed for wirewrap termination be used in solder termination applications?

(i.e. as substitutes for garden-variety through-hole parts)

?

looking at these Samtec SSA right-angle breakaway header socket strips

and they're apparently designed for wirewrap termination

digikey.com/product-detail/en/samtec-inc/SSA-132-W-T-RA/…

No idea where you got wire-wrap from a datasheet that mentions Board Mount a bazillion times

@Asmyldof digikey's listing apparently is not to be believed then. xD

When is it ever

oh, a-ha -- it's a part suffix option

-S is the standard solder tail, -W is the wirewrap, and the -RA option requires -W

sadly, Digikey is out of stock with a 2 week lead time, and Newark lists it as a manufacturer direct ship (why?!?!)

same for the gold finish...this feels like a total pile of WTF

@Shalvenay Samtec just does a lot of parts like that. Also with Digikey.

i.e. I've ordered Samtec parts from Digikey and had them shipped direct from Samtec rather than from Thief River Falls. Same thing with Arrow (or was it Avnet?).

@ThePhoton yeah -- it seems that it's a Samtec thing

it makes the lead time a total PITA though

@Shalvenay Depends on the parts. The stuff I ordered came in a couple days. Wire wrap is probably pretty low demand, though.

hrm...so why would DIgikey say 2 weeks then?

@Shalvenay Because wire-wrap is probably low demand, so it might actually take 2 weeks to get those parts (maybe they don't keep the pins in stock)

@ThePhoton nods Newark seems more optimistic though?

(2-3 business days)

Anyone here?

@Shalvenay You can always call and ask.

can anyone explain the input impedance of an op amp?

@ThePhoton worth a shot at least

@hacker804 do you want to the basic of input impedance of opamp?

Yes that would be helpful

electronics.stackexchange.com/questions/73689/… see this, might be helpful

Thank you

:)

Actually I am currently in my 2nd year of EE

And I would like some book suggestion, from a design perspective

Because in our courses although we learn a lot of theory and models but there is very little room for practical design issues

recently I have seen this, electronics.stackexchange.com/questions/616/…

What are your thoughts on The Art of Electronics

If it is not what you want, so might any other user will help you.

I am from India, and I used the books which were provided by my college.

Can you name some?

which were my local editors.

U.A.Bakshi.

ok I will look them up

What are your qualifications

I guess you are from India. Is it?

I'm in 3rd year of Electronics and Communication Engineering.

From across the border :P

Great

Border, Umm Pakistan or Bangladesh?

or China?

Pakistan

Okay :)

@Asmyldof and @PlasmaHH today was the first time I helped someone. Of course not with my knowledge but helped him. :D

@ThePhoton called DigiKey and indeed it's a 2wk lead time on their end. I suppose Newark's next on the phone-call list

@Shalvenay I keep not understanding why you USicans are so afraid of calling a supplier directly!?

@KrishnShweta As long as it isn't with cookies. Cookies are my domain!

I'm making cookies!

Not sure which yet

@Asmyldof there's a general assumption over here that 1. will get shunted off into no-mans-land if you aren't mentioning 10k units (and sometimes even if you are)

and 2. many distributors don't deal in B2C at all it seems, only B2B

also, some would probably consider it quite rude to call a business outside of the normal 9-5 business schedule

@Asmyldof Cookies!! Chocolate ones?? :)

@inkyvoyd I was looking for the questions whose having more than 10 answers in our EE.SE. So found this electronics.stackexchange.com/questions/1024/…

@inkyvoyd also the simulator you suggested me was mentioned there. I have used it and found how to see the waveform which I was unable to get previously :)

@Shalvenay You have an incredibly weird country

@Asmyldof there are the Big Five that do B2C (they all started life as small quantity catalog distributors and moved naturally into the online space): DigiKey, Mouser, Arrow-NAC, Newark, and Allied

outside of that, GLHF.

@KrishnShweta Maybe. Probably not

Cool.... make which you want :)

I get stuff directly from: Wurth (WE Direct), AMP/TE (Local Rep/Dist), Yageo (Local Rep/Dist), Murata (Local Rep/Dist)

And whichever other I need more than the sporadic from

@Asmyldof I've ordered stuff direct from Maxim/Dallas through their website -- and am about to take the plunge with Samtec even though they insist on charging me $15 for next day air ;P

The only very regular use articles I get from others are ICs (higher MOQs I almost never reach), Transistors etc (Because NXP doesn't do less than 10 reels, but happily picks up the phone), Resistors (because I have almost any value in 0603 from Multicomp in stock)

Oh! I do do ICs!

Analog

but a lot of manufacturers will just shunt you to a distro, even for samples (ON Semi's samples were through Avnet IIRC)

They supply me directly whenever I need a whole reel, mini reel or tray

But Analog only does whole packing quantities, but no HUGE amounts for direct

Maxim is actually ridiculously nice, you can order direct from them even for onesies

And Wurth is by far the easiest.

But then you do need to want to use Maxim parts

Which is a very, very verrrrryyyyy rare occasion for me.

@Asmyldof :P although sometimes they make stuff that nobody else does (like a RTC that implements the full Gregorian leap year algorithm(!))

@Shalvenay Don't need a chip for that

Plenty MCU's support full calendars and options between both popular ones and implementing leap-years, if not already in hardware, is insanely easy in software

Actually an entire calendar is laughably simple

I'm sure there's a million people open-sourcing solutions for just about any core

@Asmyldof so you set an alarm for 11:59:59 on Feb 28 and manually reprogram March 1 00:00:00 into the thing if it's not a Gregorian leap year?

You could.

You can do it entirely without calendar hardware and then it becomes even easier

Just uses a bit more RAM and an MCU that has a sleep function deep enough to give you the same 1uA losses

of which there's dozens from each brand