Learning electronics: Release the Magic Blue Smoke

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

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Mill Town: Apr 17, 2006

Hillridge posted:

I approve of this thread!

I currently work as an R&D Electrical Engineer, so I'm sure I'll be following this thread.

It can not be overemphasized how much of a difference a quality soldering iron makes when working on stuff. That $20 radioshack iron will probably solder two wires together, but there is no way you're going to solder fine pitch surface mount parts with it. If you do a lot of work with surface mount components then having a hot air gun also works well.

Also, get a little squirt bottle full of flux and apply it liberally to things you wish to solder. Do that and use leaded solder (the lead free stuff sucks) and things will go much easier.

Thanks for the info. I'm getting tired of buying new tips and irons every few months. I'm also interested in what other tools are needed for a good hobbyist setup. Heat gun and a big old pile of heatshrink tubing are definitely on my list of things to get. Should I look for anything in particular in a heat gun? Are temperature/CFM/BTUs/etc important or will whatever's in stock at the local industrial electronics store be fine?

I'm also interested in getting a vacuum rework station. How cheaply can I find a good one, and what brands should I look for?

Last question, when I started tinkering with things as a kid, my dad instilled a fear of flux in me, because ZOMG ACID. As a result, I've never used it, to this day. How bad is flux really? Will it eat my skin if I spill it on myself or just hurt a bit? What safety precautions should I take?

For other people who don't have tools yet, here are some of the things I find indispensable:
- Jeweler's screwdrivers . These are tiny little screwdrivers. Don't get the crap ones from Radio Shack, they suck and will fall apart or even be defective out of the box. I once got one where the tip hadn't been stamped or ground or whatever they do to form them, so it was just a rounded cone instead of a Phillips.
- Needlenose pliers. Obvious, probably.
- "Helping Hands." Those things with a weighted stand, a magnifying glass and two alligator clips on adjustable arms, for holding tiny stuff you're working on. They have a tendency to tip over if you even look at them funny, so fasten them to your workbench somehow.
- A jar of soldering iron tinner. This is an incredible time and frustration saver compared to tinning by hand. Everyone should have one (that reminds me, I need more). Sometimes if stuff won't fir in the helping hands for whatever reason, I just tape things to the board or my workbench while I solder them.
- 3-claw part retriever. A little round thingy with a plunger on one end and a springy metal claw on the other. You push the plunger and the claw opens up, let go and it springs back. Great for retrieving fiddly bits that you dropped into the case of whatever you're working on.

# ¿ Jan 8, 2008 22:17

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# ¿ May 1, 2024 09:18

Mill Town: Apr 17, 2006

Hillridge posted:

A good thing to do to keep your iron tips fresh and shiny is to "tin" them before turning the iron off. Basically cover the whole tip with a big glob of solder and let it cool on there. When you need to use the iron again, just let it heat up and wipe off the solder on the sponge.

Oh, that's cool, I had thought you were supposed to tin the iron about a minute after turning it on, which doesn't work so well when it's been sitting around for a while and is oxidized. That makes more sense.

quote:

By heat gun I actually meant one of these guys:

This thing is essential in reworking surface mount parts since it allows you to heat up the whole part at once. You can pop off a chip with dozens of pins in a matter of seconds, whereas I don't think you'd ever get it off with an iron. They also have a tip that fits over the end of the wand to reduce the airflow to a small tube rather than the big 1" or so opening, which is ideal for resistors and other small parts.

This works, but I solder parts almost exclusively with an iron, even the fine pitch stuff (there is a neat trick that involves dragging the iron along the pins). Have you ever looked at solder paste under a microscope? It's tons of tiny solder balls suspended in flux and looks really cool:

(Click for huge)

I have never needed a vacuum rework station for anything, but they are neat. You can save your money and buy a small manual solder sucker and a package of solder wick instead.:

I do use desoldering braid and a solder sucker, and I find they work great on single-sided boards, but take forever on double-sided boards and sometimes don't work at all. They both seem to get the solder that's on the bottom of the board, but any that's left in the hole will keep holding the component in place. I figured a powered vacuum rework station that would suck continuously would be able to get it all out. Maybe I'm just doing it wrong.

quote:

Flux is your friend. It makes everything solder related easier. The type I use around the lab is Kester 959 low residue no-clean flux. It's designed for wave soldering machines, but it works great for doing stuff by hand too. I've gotten it all over my hands when I'm working and it has yet to hurt me. I just wash up when I'm done. Don't inhale when the iron vaporizes it though.

Edit - From their site:
959
No-Clean Alcohol-Based | Fluxes

Kester 959 is a no-clean, non-corrosive, halogen free liquid flux that is designed for the wave soldering of conventional and surface mount circuit board assemblies. Kester 959 was developed to minimize the formation of micro-solderballs during wave soldering operations. This flux contains a small percentage of rosin (1%), which improves solderability, heat stability and surface insulation resistance. Kester 959 offers the best wetting and the shiniest solder joints of any no-clean, solvent-based chemistry. Kester 959 leaves evenly distributed residues for the best cosmetic appearance.

This may be a lot for someone just getting started. I went for years using a soldering gun (huge compared to an iron) on through hole projects.

Well, I definitely need to upgrade something. Desoldering a single part can take me half an hour or more if it's stubborn and has a lot of leads.

Thanks for the informative post!

Mill Town fucked around with this message at 01:15 on Jan 10, 2008

# ¿ Jan 10, 2008 01:11

Mill Town: Apr 17, 2006

Vaporware posted:

And here's the circuit from the chip manual

I think your LED might be hooked up backwards. You have pin 7 shown as LED- and pin 16 as LED+ in your first photograph, but the schematic I quoted has it the other way around.

# ¿ Sep 25, 2008 18:22

Mill Town: Apr 17, 2006

Delivery McGee posted:

If I do go the detonator route (with a few big batteries), I'm planning on wiring up a switch to pick between series and parallel on the batteries; is this possible?

Absolutely. Here you go:

Someone else should probably check this to make sure I'm not shorting anything out by accident. It's late and I'm tired.

Oh also, that's a single DPDT switch in there.

# ¿ Dec 27, 2008 09:32

Mill Town: Apr 17, 2006

mtwieg posted:

Okay I set up a filer account and I uploaded the technical report of my SODAR project. Before I make the thread on it I wanted to make sure I've got the hosting set up right. So just let me know whether this link works or not (should go to a pdf of the report).

Works fine.

# ¿ Dec 27, 2008 21:53

Mill Town: Apr 17, 2006

Delivery McGee posted:

Like ante said, any decent-sized city should have some kind of hole in the wall, or at least an electrician's supply house.

Flip up the cover, flip the switch under it, and the big button lights up, then press it to fire ze missiles/release the hounds/destroy the evidence/etc. Total cost of all parts shown (it's empty inside for now): $15 or so. The big button alone costs that much on the internet.

Depends where you are in Canada, though. Canada is loving huge. I can tell you where to find such things in Halifax, Montreal or Toronto. Are you anywhere near any of those places, BattleMaster?

# ¿ Dec 30, 2008 00:53

Mill Town: Apr 17, 2006

BattleMaster posted:

Awesome, I thought it was going to be hopeless to find something like that because Delivery McGee said his was military surplus. All the "military surplus" stuff we have here is stolen, fake, or pre-Korean War.

Anyways, I'm close enough to Toronto that it wouldn't be a big deal to make a trip one day. Thanks!

OK, what you want to do is head down to Active Surplus. I can't guarantee that they'll have the big red button, but they will have a nice assortment of similarly awesome things.

# ¿ Dec 30, 2008 08:48

Mill Town: Apr 17, 2006

Snaily posted:

I'm looking at making a dimmable LED light fixture by making a variable duty cycle square wave with a 555, and I was going to use this circuit.

However after running it in SPICE (TINA) the frequency is not constant for a given duty cycle percentage (not even for, say, 90% and 10%)! Do I just suck at simulating, am I missing something (like highly differing source/sink impedances on the output pin), or is the circuit wrong?

Do you mean that the frequency changes as you adjust the pot (this is normal) or that the frequency changes on its own without adjusting the pot (this is not normal)?

# ¿ Jan 26, 2009 18:25

Mill Town: Apr 17, 2006

Snaily posted:

Frequency changes as I adjust the pot. I was under the impression that this would not be the case (as stated below the diagram). Or in any case, I thought the frequency should be the same for 10% and 90% duty cycle if not in between.

Normally with a 555, the frequency depends on both the resistors and capacitors, so changing any one changes the frequency.

However, looking at that diagram again, it does look like they have designed it a bit differently, perhaps in a way that's supposed to avoid this. Maybe your simulation is wrong, I dunno.

# ¿ Jan 26, 2009 19:36

Mill Town: Apr 17, 2006

IfIWereARichMan posted:

(crossposted from the quick question thread)

It's just the guts of a Wagner heat gun which seems to use a standard type nichrome wire heating element, max power draw 1500 W. I want more control over the temperature in the low range than the panel will give me. My guess is that heat and fan are each just controlled by current limiting, so I need a way to limit current at like 200 - 300 watts (a guess pulled out of my rear end).

Potentiometers are out for not being rated at high enough power levels, and 225 W power resistors are $20 each at digikey, too expensive for this project.

Is this doable at all?

Resistors are absolutely NOT the right way to limit current in an application like this. Even if they were affordable or practical, the excess power bot being consumed by the heating element would be dumped by the resistor, generating... wait for it... heat. You might as well just stick part of the heating element outside the gun.

The resistive element is probably just controlled by a simple dimming-type circuit, with feedback from a thermistor to regulate the temperature. You could replace the controller with your own microcontroller, but that's kind of an involved project and probably would cost more than $20 overall.

Actually, maybe you could put another resistor in series with the thermistor to make the controller think the output temperature is higher than it is. That's assuming there really is a thermistor in a feedback loop.
Edit: wait, I think I got this backwards. We want the controller to think it's 350 degrees when it's actually 200, or whatever, which means we need to lower the resistance. So you'd need to put a resistor in parallel with the thermistor. Start with a very high value resistor and work your way down until you get the temperature you want.

If there isn't a thermistor, and it's a straight-up dimming circuit, you could probably remove all the electronic guts and just replace it with a light dimmer.

Mill Town fucked around with this message at 22:53 on Jan 28, 2009

# ¿ Jan 28, 2009 22:49

Mill Town: Apr 17, 2006

IfIWereARichMan posted:

I put a 600 watt rotary dimmer inline on the neutral lead from the power cord, allowing me to keep the control panel attached. And it worked without starting any fires! This was the major hurdle for this project, although unfortunately, the dimmer also slows down the fan, which has made it difficult to pin down the range of acceptable positions for the rotary knob.

I think the next step is to rip out the fan and replace it with another one that is powered independently.

My advice would be to put the dimmer knob in the body of the heat gun, attached directly to the heating element. Then hook the power cord up to the element/dimmer combo in parallel with the fan. Get rid of the existing circuit board entirely.

Edit: Although, since it's drawing 1500W max, you should get a bigger dimmer.

# ¿ Jan 29, 2009 06:02

Mill Town: Apr 17, 2006

ANIME AKBAR posted:

Well you could build your own dimmer with a triac and some simple external circuitry. Can't say how expensive the triac would be though.

The existing circuitry probably has a triac in it already so that's not a big deal.

# ¿ Feb 2, 2009 14:18

Mill Town: Apr 17, 2006

clredwolf posted:

if you think about it, it's the same is 'voltage is across, current goes through'.

Yeah, this. My brother works at an LED lighting shop and he's been calling me a lot recently with some "I've got these LEDs and I need to drop some extra voltage, where's it going?" type questions, and I've basically been repeating this to him. "Voltage is across things, current is through things."

# ¿ Feb 13, 2009 06:23

Mill Town: Apr 17, 2006

Plexiwatt posted:

Quick question: I've got a circuit built on a breadboard that I want to make permanent--can I just blob some hot glue over the components and encase them? It's nothing too high-current.

I know that using a proto board and soldering everything is the pro way to go but I don't have the time or my iron with me.

It seems like that should work, but 1) it's an expensive solution and you'll probably never get the breadboard back and 2) if something fails or comes loose it'll be a bitch to find and fix it. Just run out and buy a soldering iron and a perfboard. You can get ones with the same trace arrangement as the solderless breadboard so you can just transfer everything over to exactly the same spots.

ozziegt posted:

So I am messing around with microcontrollers and everything I have read said to buy BJT transistors. But the first post in this thread says MOSFETs are better. So just wondering why all the talk recommending BJTs...is it because BJTs cost about $.10 each while MOSFETs cost $2? Also, are they implemented the same way in a circuit?

The other cool thing about MOSFETs is that they don't need a current-limiting resistor on their gate (the equivalent of a transistor's base). In a circuit with a lot of outputs, this can save you a lot of soldering time.

The other uncool thing about them is that they're static sensitive so you have to be careful about handling them.

# ¿ Feb 15, 2009 01:47

Mill Town: Apr 17, 2006

Argh, some fucker in the shop lost the cap to the flux and then someone else left it near the drill press. Which someone else was using to drill aluminum.

Guess what happens when you solder a circuit using conductive flux? :argh:

# ¿ Feb 24, 2009 09:11

Mill Town: Apr 17, 2006

ANIME AKBAR posted:

aaaaaaaaaah christ

The best part was how when I took it off the bench and tested for shorts, I didn't find them. Then I'd put it back down (on a piece of paper to make sure I wasn't touching any scraps on the bench) and power it up, and it'd act fine for a few seconds until all the output transistors just turned on by themselves, and a few seconds later it would start smoking again. Or sometimes it would see a flash of light coming through the board and unplug it right away. It wasn't until I started thinking about why there were so many bits of crap in the flux that I figured out what was going on.

In related questions, what's the best way to get flux off a board? :suicide:

# ¿ Feb 24, 2009 20:23

Mill Town: Apr 17, 2006

Cyril Sneer posted:

Okay guys, a big one for ya. Wasn't sure if I should start this as another thread, but here goes.

I recently picked up this LED matrix at a surplus shop:

The only problem is I have no idea how to drive it. I've played around with it a bit and made a few discoveries. I've managed to at least figure out how the LEDs are arranged:

The entire matrix is split into a 2x8 grid, with each cell containing 8x4 (ie, 32) LEDs. Power is supplied to each column by one of the 8 power transistors on the left (you can see the thick traces running from left to right). The LEDs in a given cell are then wired to the bank of resistors (circled, on the left). LEDs along the bottom half (Row B) are wired to the lower 32 resistors. LEDs in the top half (Row A) are wired to the top 32 resistors. So, for example, if one were to apply voltage to the central pad of column 6, the LEDs in cell B6 would be illuminated sequentially by sweeping a ground connection along the bottom 32 resistors. The LEDs in cell A6 would be illuminated sequentially by sweeping a ground connection along the top 32 resistors.

Each of resistors, all 64 of them, are wired to 8 UCN5821 chips each with 8 outputs (8 x 8 = 64).

Here is a close-up of the logic circuitry:

Here the connections between the LEDs, resistors, and UCN5821 chips is clear. The ICs present are as follows:

UCN5821: 8-bit serial latch
AM26LS31: Quadruple differential line driver
SN74LS15: 3-input AND gate
M74HC238: 3-to-8 decoder.

I'm an RF guy, not a digital guy, so this is all pretty foreign to me. I basically understand everything up the UCN5821s. I have no idea how to feed data into this or how to clock it. I'm hoping that it might resemble some sort of "standard" LED matrix architecture.

Help me out guys! I really want to get one working - there are a whole lot more where this one came from!

I will provide as much additional information as requested.

That looks like the LED sign that the guys at hacklab.to recently reverse-engineered. Informative blog post here:
http://www.andrewkilpatrick.org/blog/?page_id=795

Also try their IRC channel at #hacklabto on Freenode if you have more questions.

Edit: Did you get that at Active Surplus?

Mill Town fucked around with this message at 01:11 on Mar 1, 2009

# ¿ Mar 1, 2009 01:08

Mill Town: Apr 17, 2006

Cyril Sneer posted:

My god, thats EXACTLY what I'm trying to do. And yes, I did get it at Active Surplus. Looks like I'll be emptying their stock tomorrow

You can also visit the hacklab and talk to the guys who got it working.

http://hacklab.to

# ¿ Mar 1, 2009 03:49

Mill Town: Apr 17, 2006

I'm in need of a logic analyzer that can do up to 500kHz (fortunately I only need 2 channels, I'm analyzing a proprietary serial protocol). Can anyone recommend a PIC or AVR based solution? I've seen a few plans on the Internet but I'm not sure what's good. It needs to be able to store a lot of samples (at least a few seconds worth) and I don't know which design to pick. Thanks!

# ¿ Mar 17, 2009 03:41

Mill Town: Apr 17, 2006

Delta-Wye posted:

Sparkfun sells [what sounds like] a really nice USB Logic Analyzer, which is overkill for what you're doing now but it might be worth investing in for the long run. I know I've been looking to invest in one since I first saw it.

I've basically got a pile of AVRs and PICs at my disposal thanks to the local hackerspace, hence my desire to roll my own. This one does look pretty nice, though, and I'll consider it if I can't find anything else. Thanks!

# ¿ Mar 17, 2009 04:11

Mill Town: Apr 17, 2006

Delta-Wye posted:

So I'm building a multichannel light dimmer, and I need 5V for the PIC from AC, but I don't have space in the box for any of the transformers I have handy. Is there a neat trick to get regulated 5v from AC other than your typical transformer->rectifier->filter->regulator circuits?

Cut the jack off a 5V cellphone adapter that you don't need any more.

# ¿ Mar 20, 2009 05:42

Mill Town: Apr 17, 2006

Nerobro posted:

An audiophile company could fund ALL of our stuff. ;-) Who wants to make the website. I'm handy with cable ends...

On a "I'm a teacher" note. Yeah.... me teaching. Laugh. I had my roomie build his first vreg circuit. And then use that to feed a 555 timer to flash a LED. He then did some experimenting. He found out that LED's have different voltage drops when he put a red LED with his white LED's and only the red LED lit.

Now here's the fun part. While I was out yesterday, he figured out that putting a resistor on the red led would bring it's voltage drop up to match the white leds.

I'm kinda proud of him.

It's funny, I was just thinking last night, "Man, I'm tired of being the guy who always tries to tell people about scams and flimflam and gets argued with. Maybe I should just throw my morals out the window and start selling ~~magnets with velcro on them~~ ELECTRON FLOW ENHANCERS to audiophiles for $100 each."

I've got hundreds of bits of velcro left over from some old telco gear. Who's got the magnets?

# ¿ Mar 22, 2009 23:04

Mill Town: Apr 17, 2006

Sweevo posted:

Going back a dozen pages or so: I've got an op-amp driving a MOSFET to switch a 5A load. Can I put an indicator LED in parallel with the load, or do I need to switch it separately?

Nothing wrong with using the LED there, no.

# ¿ Mar 27, 2009 15:55

Mill Town: Apr 17, 2006

TwoShanks posted:

I am currently building several robots which are attracted to light and have ultrasonic collision sensing. I'm now trying to think of a way to make the robots able to find and move toward each other in certain circumstances. I was going to use infrared emitters and detectors but the lights produce too much IR and overwhelm the LEDs.

Any ideas for sensing systems to allow the robots to find each other? The system also needs to be as cheap as possible.

Put a few kHz or so square wave out the LEDs and a high-pass filter on the detector?

e: high

Mill Town fucked around with this message at 00:22 on Mar 29, 2009

# ¿ Mar 29, 2009 00:16

Mill Town: Apr 17, 2006

CptAJ posted:

Quick couple of questions here. First of all, I don't really know much about electronics but I can't stop myself from breaking stuff open. That said, I was recently playing a mighty fine game of CIV4 and my computer crashed horribly. Seeing as the screen went to poo poo and I knew the videocard's fan was busted, I figured it was overheating. I decided to remove the fan and play mcguyver by putting a casefan pointing towards it. Thats when I noticed 3 bloated caps. Some of them have already started oxidizing or whatever.

So, any reasonable person would keep using the card for regular computer activities and wait to get a replacement card. But I don't have a car until tomorrow and I'm very bored. Obviously this meant rumaging through the boxes of crap in the house looking for some scrap that had matching caps. Well, the search paid off. I found the matching caps (I think) on an old motherboard. I used the soldering iron to remove them without too much trouble.

And this is where you guys come in.

- Is this advisable at all?
- How do I test the caps? I have a multitester here but I don't really know how to use it.
- Caps on the card: 6.3v 1000�f Skywell SHT (M) 105�C
Rumaged caps: 6.3v 1000�f G-LUXCON 0067 (M) LZ 105�C
Will they even work?

Thanks for the input =)

Yes, this is advisable. Worst thing that happens is you screw up the card and have to buy a new one, which you were planning to do anyway. Those caps are compatible, so no problem there. The basic guideline when replacing caps is: same capacitance, same or higher working voltage.

The only downside is that you can't really test them unless your multimeter has a capacitance test function. Does it?

# ¿ Mar 29, 2009 00:25

Mill Town: Apr 17, 2006

Bush Ant posted:

mine plays the mario theme song

not really but if there was one that did I would totally buy it

edit: it actually shouldnt be too hard to implement, fitting it all in the case would be another matter, I will look into this further

ATtiny13 + piezo buzzer

# ¿ Apr 3, 2009 23:06

Mill Town: Apr 17, 2006

Delta-Wye posted:

Here is a circuit only a mother could love!

This is so ugly I have no idea why I'm showing you

I did some back-of-the-envelope calculations, and I think my line-voltage->5V regulator is approximately 2.2% efficient. It's not a big deal as the power draw isn't huge, and I think the paralled 2W resistors should be a-okay.

One of my EE professors came into lab to see what I was tinkering on, looked at the project, looked at the calculations on the white board (including the drawn schematic), and after pondering this monstrosity for a few minutes said something along the lines of "If you show that to an electrician, he will never respect you again," and then walked out.

I wonder if the same applies to EE professors

I was working on the firmware a bit today, it seems like it is going to work! I hope this is what you were imagining Bush Ant, it was a fun idea to put together. I've only blown 2 fuses and popped the breaker once (all through sloppy probing).

EDIT: I vote microprocessor with a lot of memory and a DAC and a small amp. Install it between the current circuit and the speaker - when it sees the attempt to drive the speaker, it starts dumping values out through the DAC into a simple amp that then drives the speaker in turn. Seems like it would work.

what the christing rear end :psyboom:

You know, you could definitely fit a small switching supply in that large an amount of space. There are toroidal transformers that are smaller than that bank of resistors.

I didn't really think about it when you first posted, because I have a hell of a time visualizing things. I'm really terrible at it. But now I can see how much space you have to work with.

# ¿ Apr 6, 2009 07:09

Mill Town: Apr 17, 2006

Cyril Sneer posted:

I'm having a problem sourcing a common connector.

DigiKey and Mouser both offer these headers:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A1927-ND

that's the 640457-4 and the 640457-5. These are 4-position and 5-position headers.

However I'm having a hell of a time finding the appropriate mating piece on either site. DK lists the mating products, and it seems like 644512-4 is the appropriate one, except its listed as non-stock. Indeed, this is the case for both DK and mouser!

Why would they carry the header but not the connector?

Do any of you guys know where I could find the appropriate connector for the 640457-4/5 header? It's a pretty common part!

If you scroll to "mating connectors" and click "more" you can find some that are in stock. eg. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19093-ND

Edit: wait, that's wrong. You have to order 1000 of those. Hm. I'll keep looking.

# ¿ Apr 13, 2009 08:32

Mill Town: Apr 17, 2006

Sabretooth posted:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A31129-ND

Did you hit 'more' on the Mating Products section on Digi-Key? There are a ton of connectors there, and not all of them are non-stock.

e: too slow

Here we go, finally found one that's not non-stock.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A30816-ND

Ugly color, though :P

Edit x2: here's a white one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A31004-ND

Edit x3: Various other colors are also available. I'm partial to red:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A31122-ND

Mill Town fucked around with this message at 08:40 on Apr 13, 2009

# ¿ Apr 13, 2009 08:36

Mill Town: Apr 17, 2006

ozziegt posted:

I have an old set of Cambridge Soundworks DTT2500 Speakers. Recently some channels are cutting out...they just stop working, and if I fiddle with the knobs sometimes they cut back in only to cut back out again. Is there any basic thing I can look into and see if it will fix it? I've seen a couple internet posts which suggest it might be dirty potentiometers in the knobs...does that sound reasonable?

Dirty pots is definitely reasonable. So is broken wires as jonmitz suggested. Open them up and spray some contact cleaner into the pots. If it doesn't get better, keep poking and flexing wires until you find ones that make the sound cut out, then replace them.

Edit: most likely candidates are the wires that are outside the housing, the one that connects to your PC and/or the ones that go to the satellite speakers.

# ¿ Apr 14, 2009 23:08

Mill Town: Apr 17, 2006

Zaxxon posted:

why the hell are crimping tools so drat expensive? Anyone have a clue?

I think it's because they sell them to contracting firms, which is kind of like selling to the army.

# ¿ Apr 16, 2009 06:11

Mill Town: Apr 17, 2006

Scarboy posted:

I've been designing a simple PCB that is pretty much a breakout for 8 CMOS4066 chips and I've run into a few little issues.

Firstly, battery power. If I have dual supply 4066 ICs can I pass the positive and negative leads from a CR2032 or 2 AAs to power them? Will -3V on the enable lines be logic low? I haven't had a chance to test this since I don't have any dual supply 4066 ICs lying around. I don't really have 0V on my board, I can get it from elsewhere but it would be nice if I could just use the negative terminal from the battery.

Next, how can I calculate how long I expect the battery to last if the battery is just feeding these 4066ICs? The enable lines will be pulled down to -3V with 10k resistors 99% of the time, I don't know if that changes anything. On most of the datasheets I look at I can only find the leakage current and quiescent current (not really sure what that is) and they are usually around 1uA for a 3V supply. To calculate battery life in hours should I just do battery capacity / (2uA (for good measure) * 8)? I don't want to put in a power switch and I just want this thing to last a long time like a remote control.

My last issue is with finding connectors. For each set of 4 ICs I have two 16 pin headers (16x2), what better options do I have for connected wires other than soldering them directly or hot gluing them into a female header? I found this on digikey http://search.digikey.com/scripts/DkSearch/dksus.dll?FullDetail&name=A28757-ND#usewithchildren but I have no idea how to use it. I suppose I need a crimper and plugs for inside? I'm also wondering if putting two of these right on top of each other will be a space issue since they are keyed.

Is there such a thing as a dual supply 4066? Got a datasheet link? But if so, what you're proposing should work. Actually, a schematic might be helpful here. Do you need or have a virtual ground?

Quiescent current is how much current the chip draws when it's not switching. The switching current (at least in the 4066 datasheet I'm looking at) is calculated as part of the total supply current, and is dependent on the switching frequency. If you're not going to be switching very fast or very often, it won't matter. It's microamps per kilohertz.

Are you already stuck with this 2x16 pin header design? You should be able to get a 2x16 header and ribbon cable although I'm having trouble finding one on digikey.

# ¿ Apr 26, 2009 00:03

Mill Town: Apr 17, 2006

Otacon posted:

The LED I removed was a blue LED with no resistor (I checked under the heat shrink) which led me to believe it'd be a direct swap. I bought a 12v red one at Radioshack, and it wasn't bright at all, even after moving moving the molex pins to provide 12v. Then, I bought these - 3 of them - and moved the molex pins back to 5v. Each LED was blown.

I need the following - a clear LED that displays a red color that is very bright and will work with either 5v or 12v. Can anyone help?

Your blue LED and your 12V Radio Shack LED had built-in resistors, which is why they did not burn out.

Buy some more of those red LEDs, and put one in series with a resistor of 150 ohms or so on the 5V supply.

Full details on wtf is going on are available at this link:
http://www.kpsec.freeuk.com/components/led.htm

# ¿ May 3, 2009 07:54

Mill Town: Apr 17, 2006

CGameProgrammer posted:

Can someone tell me how to splice together speaker wire? I have headphones and attempted to shorten the wire for them but I can't figure out how to reconnect the two wire ends after cutting out a section in-between. When I strip the insulation, I get what appear to the naked eye to be one copper wire and one green-insulated wire, but macro mode with my camera reveals they're both woven metal wires with something else inside... this whole thing connects to my ipod via a simple 2.5mm jack so it can't be complicated. But no matter what I do, I can't get any sound to come out of my headphones.

Here's a close-up photo (my host). It's hard to see, the flash makes things bright, but basically there appears to be really tiny light-gray strands inside the woven copper and green wires. Don't know if the gray stuff is uncolored wire or if it's just fabric for strength. Also don't know how the copper and green wires stay insulated from each other, they appear to be right next to each other in the black insulation.

What do I do?

EDIT: Nevermind. A google search with a different search term turned up this SA post on the same subject. Apparently they're ordinary wires with a plastic coating to prevent them for shorting against each other, and I guess I'll just have to go ahead and solder them together and then try it again.

EDIT AGAIN: It worked! Yay. Heating the wires with a 40W soldering iron in an attempt to burn off the coating, then twisting them together, actually did not work, but when I then soldered that twisted connection, it suddenly worked.

For future reference, fine-grit sandpaper can help you remove the epoxy that's coating the wires. You can also burn it off with a cigarette lighter.

Edit: And that grey stuff is indeed fabric, for strength.

Mill Town fucked around with this message at 10:41 on May 3, 2009

# ¿ May 3, 2009 10:34

Mill Town: Apr 17, 2006

Delta-Wye posted:

I would guess this is the LCD connection here:

Click here for the full 640x480 image.

As far as how the LCD connects to it, I have no idea. I would also guess that it is a HD44780 or similar under the black epoxy, but it's hard to tell.

Can you get a non-blurry picture of the board and the back of the LCD? Sounds like a cool project, I would like to be able to help you but those pictures are pretty hard to make out.

I've seen those before, the rubber strip actually has conductive bits in it. Try taking an ohmmeter to it and you should find alternating bands of conducting and nonconducting material.

It will be next to impossible to rig up an extension that makes a good connection, though. Rather than extending the wires to the LCD, why not extend the wires to the ~~weight~~ position sensor?

Edit x2: That page you linked also explains how the data signal works. With some effort, you could probably write a program for an Arduino or other �C that reads the data and outputs it to an LCD or LED display.

Mill Town fucked around with this message at 06:37 on May 21, 2009

# ¿ May 21, 2009 06:33

Mill Town: Apr 17, 2006

Tmavomodry posted:

Does anyone have any source for cheap IR pass filter material?

Exposed developed film negatives.

Edit: apparently two layers give good results: http://www.davesastro.co.uk/equipment/irpass.html

Mill Town fucked around with this message at 20:04 on Jun 11, 2009

# ¿ Jun 11, 2009 20:00

Mill Town: Apr 17, 2006

BattleMaster posted:

I don't know how that function works, but you need to wait until the SPI module is finished before setting the I/O bit high again. It looks like all the function does is load the output register and tell the module to transmit, without waiting for completion. ~~There is likely a function that you can use to find out if the module is done transmitting or not that you can use with a while loop to wait until it's done.~~ Edit: Oh, there's no function for waiting? Take a look at the data sheet and figure out what bit in what register indicates that SPI transmission is complete and just check that in a while loop or something.

I don't know any specifics about the libraries you're using, though. For basic things like SPI I just roll my own code instead of use the included libraries for it. I mean why call a function when all you need to do is load a register and set a bit?

Yeah, looking at the datasheet, I think just waiting for SPIBUSY to clear is the best thing to do.

# ¿ Jun 19, 2009 23:47

Mill Town: Apr 17, 2006

SynMoo posted:

Hopefully you guys can help me out! I'm trying to come up with a simple circuit and it's been awhile and I want to bounce my ideas off of you guys.

I'm trying to drive an LED that is built into a switch assembly and has a resistor of unknown value inside. The LED is driven at full brightness when 12v is applied. I want to be able to light this LED at full brightness using a source voltage of 3v. Normally, I would just use a relay for this application because I'm more familiar with them, but I feel a transistor is more appropriate as the LED could be flashing several times per second in certain situations.

If I understand correctly, I want to connect the anode side of the LED assembly to +12v, the cathode side of the assembly to the collector, the emitter to ground, and the base to my 3v source. Am I on the right track here?

What model transistor would suit me best? I essentially want to be sure that I'm saturating the base to get full brightness, but I don't want to burn anything out of have heat issues either. Something I could pick up at the local radio shack for less than a buck would be ideal.

Thanks for the help!

Yeah, you can use a cheap 2N2222 for this. The Rat Shack should have them.

Don't forget to use a resistor on the base. Somewhere around 1k should do the trick.

# ¿ Jun 29, 2009 16:17

Mill Town: Apr 17, 2006

SynMoo posted:

Awesome, thanks!

I believe the 3v output already has a resistor as it is meant to drive an LED, should I still slap a 1k on there anyway?

Yeah, the resistor for an LED on 3V will be pretty tiny.

If you find your transistor doesn't fully conduct, lower the resistor value.

# ¿ Jun 29, 2009 19:14

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# ¿ May 1, 2024 09:18

Mill Town: Apr 17, 2006

ANIME AKBAR posted:

I work at a company called alphamicron, whose proprietary thing is liquid crystal shutters for use in sunglasses/visors/windows/etc.

You should talk to this guy, he's looking to do something like that on the cheap.

Got any slightly damaged engineering samples around?

# ¿ Jul 7, 2009 04:05

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

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