|
Maxim has a nice app note for "Audio Gain Control Using Digital Potentiometers." Naturally it's all maxim parts, but they also give you the characteristics to look for.
|
#
?
Jan 10, 2013 20:45
|
|
|
|
| # ? May 9, 2024 07:58 |
|
|
Does anyone know of any source of the PL2303TA chip in the SSOP28 package? I can't find it on Farnell, RS, Digikey or even eBay. E: This site http://www.actisys.com/Downloads.html has a workaround for Windows 8 that uses a driver that doesn't seem to bluescreen every time I unplug the device. longview fucked around with this message at 21:24 on Jan 10, 2013 |
|
#
?
Jan 10, 2013 21:12
|
|
|
icantfindaname posted:So I've wanted to get into electronics for a while, and seeing this made me wonder if making a copy of it would be a decent beginner project? I don't have any electronics experience so I don't expect to throw it together in an afternoon. But other than that, just go buy a soldering iron / some solder, the parts and take a crack at it? I am a fan of getting people to buy a simple kit with all of the parts included to get started into electronics. Like a build your own radio type of thing. They are pretty cheap and easy to do and will give you some experience in electronic soldering, while also giving the satisfaction that you made something.
|
|
#
?
Jan 10, 2013 21:58
|
|
|
Soldering is something you need to learn how to do effectively, and learning early will save you headaches and burnt fingers later on.
|
|
#
?
Jan 10, 2013 22:03
|
|
|
NoiseNoiseNoise posted:I am a fan of getting people to buy a simple kit with all of the parts included to get started into electronics. Like a build your own radio type of thing. They are pretty cheap and easy to do and will give you some experience in electronic soldering, while also giving the satisfaction that you made something. Adding to this: There are kits available that contain non-functional parts and shoddy circuit boards that are extremely cheap and are literally just meant to teach you how to solder (and fix bad solder joints). It's a decent option if you can find them and you're worried about breaking something you'll actually want to use later. Also, if you're getting a kit, grab something you'll actually have an interest in using (even if it's just playing around) instead of just the first or cheapest thing you see. I dropped a few extra bucks to get a FM transmitter kit instead of an LED flasher, and I actually had an incentive to spend the half hour I took fixing my crappy solder joints until the thing worked. It made a world of difference in actually motivating me to learn to solder properly.
|
|
#
?
Jan 11, 2013 07:21
|
|
|
NoiseNoiseNoise posted:Soldering is something you need to learn how to do effectively, and learning early will save you headaches and burnt fingers later on. I'm just learning this myself and can't agree enough. There is nothing more aggravating than doing it wrong and ending up with a lovely looking cold joint, or worse. My "favourite" is when I'm soldering some thru-hole component and I end up with a big blob of solder on the end of the component wire and it just refuses to flow down to the PCB. I'm sure it has something to do with oxidation and all that jazz. Slowly but surely I'm getting better at soldering, but I've got a long way to go.
|
|
#
?
Jan 11, 2013 17:51
|
|
|
Usually when it refuses to flow the pin is on a ground or power plane which can soak up and dissipate a lot more heat. Try using a wider tip in those cases.
|
|
#
?
Jan 11, 2013 18:01
|
|
|
Hmm, good call. I actually use a super fine tip because it's just easier for me, but I can see why that might be a terrible idea. I want to pick up a chisel tip of some sort. I hate the wide conical tip I have because it just feels really inaccurate, but I think a chisel tip that is wide but still sharp feels like it would be a perfect compromise.
|
|
#
?
Jan 11, 2013 18:06
|
|
|
For through hole work I prefer a 2.2 mm wide chisel tip, it has enough mass to solder heavier wires and works well for ICs.
|
|
#
?
Jan 11, 2013 18:13
|
|
|
priznat posted:Usually when it refuses to flow the pin is on a ground or power plane which can soak up and dissipate a lot more heat. Try using a wider tip in those cases. Nah, I've seen this far more from lack of flux. A hole with bad thermal isolation from a plane will more often give you a chunky-looking cold solder joint, since it will start to wick onto the the copper, and then stop.
|
|
#
?
Jan 11, 2013 18:27
|
|
|
Or the pad just isn't being heated at all. I've taught a ton of people to solder and usually they are either using a dry tip (no heat conduction) or only applying heat to the end of the lead and not the board (board is cold). http://www.circuitrework.com/guides/7-2-1.shtml If you're doing this, I'm not sure how you'd get that effect unless your tip is tiny or your pad is connected to a massive copper pour.
|
|
#
?
Jan 11, 2013 20:09
|
|
|
Slanderer posted:Nah, I've seen this far more from lack of flux. A hole with bad thermal isolation from a plane will more often give you a chunky-looking cold solder joint, since it will start to wick onto the the copper, and then stop. Yeah, flux it up! And then don't be afraid to wash your board with hot water and then rinse with DI water and let it dry. Clean boards are the best boards.
|
|
#
?
Jan 11, 2013 20:45
|
|
|
Those are also good tips but I stand by often people use tips that are too narrow for the application. You can actually get a lot done with a fairly chunky one. Also the dry tip, good call. I see that a lot (and not tinning the tips afterwards which drives me mental).
|
|
#
?
Jan 11, 2013 20:51
|
|
|
I know nothing about flux. Is it all the same or do I want a specific type of flux if I'm just working with through-hole components or what? A lot of my components are like 10+ years old (on the optimistic side) so I assume that oxidation is a huge problem with my soldering. If I just go buy a generic flux pen off ebay or newark, will that do the trick or should I be more discerning?
|
|
#
?
Jan 11, 2013 21:46
|
|
|
Martytoof posted:I know nothing about flux. Is it all the same or do I want a specific type of flux if I'm just working with through-hole components or what? A lot of my components are like 10+ years old (on the optimistic side) so I assume that oxidation is a huge problem with my soldering. If I just go buy a generic flux pen off ebay or newark, will that do the trick or should I be more discerning? There are a bunch of kinds of flux, but gently caress if I know what they all are. If you're curious, though, you can read this For most purposes, flux pens are great. 2 choices are: http://www.amazon.com/Kester-951-So...STER+ROSIN+FLUX http://www.amazon.com/Kester-Solder...STER+ROSIN+FLUX I honestly can't remember which I have at home...regardless, I think they differ in their solubility (water vs. alcohol). I think RMA flux can be left on the board in a lot of cases, but not if you want something that will last a few decades or will be in a very humid environment. I don't remember the downsides of no-clean flux--either it actually (and deceivingly) needs to be cleaned, or it gives you cancer, or something. Electronics, you know?
|
|
#
?
Jan 11, 2013 22:01
|
|
|
I found this video pretty helpful when I was picking up electronics again: https://www.youtube.com/watch?v=I_NU2ruzyc4 I think the same guy made a surface mount soldering video that was linked a few pages back.
|
|
#
?
Jan 11, 2013 22:10
|
|
|
We use PADS for layout at work. There's no way I'm shelling out that much dosh for home designs. OrCAD and Eagle suck (and Eagle's hobbyist version is way expensive for what it is). What free or cheap program should I use for PCB layouts?
|
|
#
?
Jan 11, 2013 22:14
|
|
|
I've posted this before, but I have this one and it's great. That guy on eBay still sells them for ~$6 shipped. Otto Skorzeny posted:We use PADS for layout at work. There's no way I'm shelling out that much dosh for home designs. OrCAD and Eagle suck (and Eagle's hobbyist version is way expensive for what it is). What free or cheap program should I use for PCB layouts? Check out FreePCB; it's what I migrated to from Eagle when I needed more than 2 drat layers and in my opinion is both more powerful and easier to use. I briefly tried KiCAD and it was a nightmare, and all of the other freeware programs I found like DesignSpark were junk. e; It doesn't have a schematic editor, but using TinyCAD to generate a netlist and importing it is easy enough. DethMarine21 fucked around with this message at 22:46 on Jan 11, 2013 |
|
#
?
Jan 11, 2013 22:23
|
|
|
Otto Skorzeny posted:We use PADS for layout at work. There's no way I'm shelling out that much dosh for home designs. OrCAD and Eagle suck (and Eagle's hobbyist version is way expensive for what it is). What free or cheap program should I use for PCB layouts? Eagle 
|
|
#
?
Jan 11, 2013 22:40
|
|
|
Otto Skorzeny posted:We use PADS for layout at work. There's no way I'm shelling out that much dosh for home designs. OrCAD and Eagle suck (and Eagle's hobbyist version is way expensive for what it is). What free or cheap program should I use for PCB layouts? I'm also looking for for alternatives to Eagle. There seem to be lots of software out there, the main ones that are free/cheap I found were KiCad, DipTrace & DesignSpark. I was leaning towards trying DesignSpark, does it have any major downsides?
|
|
#
?
Jan 11, 2013 22:41
|
|
|
For small designs we've been using PCB123, but the caveat is you have to get the boards built by them. They do a nice job though, we've done several small boards and have had no problems. Anything more complex than 6 layers we use orcad and contract out the layout for the high speed stuff, though. The good tools are so ridiculously priced it just isn't worth it for the number of boards like that we do. http://www.sunstone.com/pcb123.aspx The schematic part of the tool is kinda ehhh but the layout is quite well done. It's all integrated with their flow so it'll tell you exactly how much the cost per board will be.
|
|
#
?
Jan 11, 2013 23:08
|
|
|
Do never use PCB123, vendor lock-in is bullshit. I've seen people use gEDA (I think?) to do opensource layouts. They wanted foss software to do it so Eagle was out, KiCAD has got to be the worst piece of software ever written GUI-wise (it's up there with GIMP but a good portion of the userbase and documentation is in French) but the boards made with gEDA worked fine.
|
|
#
?
Jan 11, 2013 23:39
|
|
|
sixide posted:Air will rush in down the center of the coax given sufficient pressure differential (more than a few psig) unless the connectors have a strong seal at both ends. Basically, don't run cables straight through your bulkhead. I don't think I have to worry about air rushing down, as the space between the outer and inner sheath in the coax is packed pretty tightly with a dielectric (and I'm going to be sealing off the dielectric with epoxy on each end when I cut the outer layer off to solder and crimp). That connection might work, actually. I talked it out with another grad student, and I'm thinking about doing something like this:  The bottom attaches to where the wires come out of the top of the cryostat, seen here. Attached to this is a piece of metal that converts the smaller NW10 opening to a NW40 opening, which is sealed with an o-ring shut. The top bit is a piece of aluminum that I'll have made to fit in the NW40 flange and drill holes into to have the connections go through. I'm wondering now if I'll need something like you posted, or if I could seal it somehow with epoxy and a thru-hole connector. Do you think with the plug you posted I'd need to have SMA connectors/plugs on both sides (like they do in the pdf), or could I solder the coax on the vacuum side right to the hermitically sealed pin? SMA connectors/plugs, while not terribly expensive, add up with you're buying them in multiples of 8. This is similar to our current set-up minus the coaxial connections, as shown here. I finally got the cryostat system out and was able to take some measurements, and I think I might have to revise my plans for the bottom (extremely cold) half due to space constraints. I have the feeling the SMA connectors will be too large. Here's an image of what I'm talking about :  (5" long)A close-up of the current (as in time, not electrons) 20-pin connector with non-coaxial connections:  The signal heads down about 6 feet into this area, and then needs to go into some kind of connector that can be detached. The wire should end in a permanent connection (one that is never removed), which the detachable sample holder can plug into. 8 SMA connections are too large to fit in this area. I'm now thinking maybe SMB connectors (although they aren't threaded). The diameter I have to work in:  (1.5")Finally, the sample holder:  (open) (shut)My main question is this: How badly would the signal degrade if I didn't have RF connectors? The signal has to travel about 6-7 inches before it gets to the sample holder (including wrapping the wire around at the bottom to thermally couple the wire to the coldest part of the fridge). PDP-1 posted:I don't know a lot about this subject myself, but the lab down the hall does high frequency work in cryogenic/vacuum environments and I could try to corner one of their folks and ask what they'd use. I'm interested to know the answer myself. Basically, yep! I do measurements on electronic noise, so the signal is actually originating from inside the sample and coming out. We aren't dealing with large signals here, the largest currents we ever really send in are on the order of a hundred microamps. We use a He3 system in a He4 dewar, so we get down to temperatures around 250mK. Thermal load isn't really an issue, the main point of concern is to make sure the connections are thermally coupled to each stage of the fridge (hence the wrapping on the very bottom). If I can avoid using discrete connectors for each signal line like SMA or SMB that would be ideal, as I'm only using them out of lack of knowledge on how badly it would affect my signal otherwise.
|
|
#
?
Jan 11, 2013 23:48
|
|
|
Insurrectum posted:I don't think I have to worry about air rushing down, as the space between the outer and inner sheath in the coax is packed pretty tightly with a dielectric (and I'm going to be sealing off the dielectric with epoxy on each end when I cut the outer layer off to solder and crimp). quote:Do you think with the plug you posted I'd need to have SMA connectors/plugs on both sides (like they do in the pdf), or could I solder the coax on the vacuum side right to the hermitically sealed pin? SMA connectors/plugs, while not terribly expensive, add up with you're buying them in multiples of 8. quote:The signal heads down about 6 feet into this area, and then needs to go into some kind of connector that can be detached. The wire should end in a permanent connection (one that is never removed), which the detachable sample holder can plug into. 8 SMA connections are too large to fit in this area. I'm now thinking maybe SMB connectors (although they aren't threaded). quote:My main question is this: How badly would the signal degrade if I didn't have RF connectors? The signal has to travel about 6-7 inches before it gets to the sample holder (including wrapping the wire around at the bottom to thermally couple the wire to the coldest part of the fridge).
|
|
#
?
Jan 12, 2013 00:52
|
|
|
At 100kHz you should be OK with a twisted pair line and phone line style connectors ( like rj45). You don't need SMA yet. You could probably even get some sealed parts for underwater installations. Water always creeps through your lines. Especially if you are sure that it won't.
|
|
#
?
Jan 12, 2013 01:29
|
|
|
Insurrectum posted:My main question is this: How badly would the signal degrade if I didn't have RF connectors? The signal has to travel about 6-7 inches before it gets to the sample holder (including wrapping the wire around at the bottom to thermally couple the wire to the coldest part of the fridge). I wouldn't be concerned about signal integrity at all for only 6-7 inches when your max BW is only 100 KHz. At those distances you're so far below your maximum wavelength that you don't have to worry about transmission line effects. What I would be concerned with is picking up stray noise from somewhere else and having that mess up your measurement. You can buy micro-coax (<2.0 mm diameter) that could just be soldered at each end if you want to avoid using a standard connector and you need something small. You'd still need a way to vacuum seal it, but that would be a problem with any typical connector. As long as you have a connector with a reasonable number of pins, you should be able to intermix signals and ground to provide reasonable isolation, so I wouldn't bother to restrict yourself to only RF style connectors. I know samtec has some IP68 rated connectors, so they might even be able to provide some amount of sealing (I doubt they're rated for vacuum but you could always ask). I think samtec does custom cable assemblies as well.
|
|
#
?
Jan 12, 2013 01:55
|
|
|
Otto Skorzeny posted:We use PADS for layout at work. There's no way I'm shelling out that much dosh for home designs. OrCAD and Eagle suck (and Eagle's hobbyist version is way expensive for what it is). What free or cheap program should I use for PCB layouts? Eagle Pro  gEDA is an option I've seen other people use, but I've heard it can be pretty buggy and has tougher learning curve than eagle.
|
|
#
?
Jan 12, 2013 18:07
|
|
|
I need to design a system that can be submersed to a minimum of 200 meters, preferably 600 meters or more, sea water, it needs to stay under for up to 3 days. The system needs to be submersible, it needs to be able to sink, stay under for a given period and then rise to the surface and send its position over a system like APRS or AIS. I was thinking it might be possible to buy containers that are rated for certain immersion depths? I'm not sure what to google for here. The radio portion will pretty much require an antenna that's vertically polarized and as high above the water line as possible to reach the VHF receiver station, is it possible to find panel type RF interconnects or antenna chassis mounts that can be used under water? An SMA connector might be nice, if we could seal up the screw connections with silicon glue? Single frequency monopoles aren't extremely complicated, but does anyone know what kind of RF ground sea water is? A ground wave antenna might work better if the sea won't act as good ground. To make it ascend we'll probably drop some ballast using some kind of electromechanical system, none of this is set in stone yet and obviously the salt water makes everything more difficult but ideally we'd like a hook type thing that's held in place electrically, so that any battery failure makes it ascend automatically.
|
|
#
?
Jan 12, 2013 19:04
|
|
|
I used to know some guys who made submarine antennas. They had custom made Radoms made out GRP. I also think there is a milspec connector type for this sort of application. If you know some people in milcom you should call them. But all those things pretty expensive. The impact of sea water is very much frequency dependent. For the surfacing you might want to try a balloon and a bottle of compressed gas, like they use to emergency surface a submarine.
|
|
#
?
Jan 12, 2013 19:42
|
|
|
As a matter of fact I do know an ex military communications guy, I might give him a call. Gas was my first idea, but won't the compression effects of the water reduce the volume to a fraction of the volume at the surface, meaning we would need a very large amount of gas and a pressure relief valve to prevent it blowing up as it decompressed? If we need 60 liters of gas to surface a kg or two of negative mass then the weight of the container might be a deal breaker. A funky idea we had was to use a permanent magnet in the chassis and then attach a bit of scrap metal, then we'd have an electromagnet of opposite polarity to temporarily demagnetize it and let the metal go, I don't know if it's practical but it's a cool idea.
|
|
#
?
Jan 12, 2013 19:59
|
|
|
Anyone have some recommendations on a nice high precision multimeter in the $100-150 range? The specs on this Protek 608 look pretty sweet for $130. According to the manufacturers website this model is discontinued though this store still has some in stock. The replacement model Protek 6500 doesn't seem to be available for less than $200 http://www.tequipment.net/Protek608.asp datasheet http://www.tequipment.net/pdf/Protek/608.pdf I'm thinking about pulling the trigger on this unless there's any other recommendations.
|
|
#
?
Jan 12, 2013 21:50
|
|
|
EEVBlog did a bunch of review videos on multimeters in that range, personally I have a Fluke 17B that works pretty well in that range. Compared to my calibrated meter it was pretty much spot on IIRC, not amazing resolution though.
|
|
#
?
Jan 12, 2013 22:39
|
|
|
Yeah I don't know too much about the market for DMMs since I've never had to buy one (I've always had access to or been provide with a Fluke 87 V), but buying a discontinued item seems like a bad idea to me.
|
|
#
?
Jan 12, 2013 23:27
|
|
|
Inductor/DC-DC converter question here, for you analog experts: I got a LT1302 boost converter sample that I'm planning to build an iPhone charger around. Problem is, I don't have any 10uH inductors and can't really justify putting an order in to Digikey or Mouser for a single $0.50 part. I do have some ferrite toroids in my junk box. Is there any compelling reason I shouldn't wind 3-4 turns of wire on a toroid and use that as the inductor? The datasheet for this IC says the inductance value isn't critial, you just want low DC resistance and a core that won't saturate easily.
|
|
#
?
Jan 12, 2013 23:33
|
|
|
longview posted:As a matter of fact I do know an ex military communications guy, I might give him a call. I like the electromagnet, if it fails you just wind up with it floating to the surface too early and you try again, whereas if the balloon fails you lose it forever. Of course if you can't demagnetize it enough you also lose it forever, so you better be sure it's a good electromagnet, maybe build in some logic to try the electromagnet a few more times if it doesn't detect itself ascending the first time (in case the scrap metal falls off but then gets stuck to the permanent magnet again once you turn the EM off)
|
|
#
?
Jan 13, 2013 03:13
|
|
|
Insurrectum posted:cryostat stuff I chatted up one of the folks in our mK lab who runs a LHe3/4 dilution system that sounds like it's similar to the one you use. They use bulkhead connectors to go from room ambient into a header box on the top of the cryostat and then a second bulkhead from the header box down into the cryogenic environment. The header box sometimes has a dry N2 bleed line into it so the inside is non-condensing as the wiring from the cryostat might be cold enough to frost up or condense water on the connections. Once inside the cryostat the cabling is wound around the pumpout line so that any conducted heat is transferred to the cold gas exiting the system (it looks like you have that part covered). On the cold end of the cryostat they had some G10 DIP socket connectors that served as a dual connector port and sample holder. I have no idea if any of that is useful for you or not but it was fun to have an opportunity to hang around the mK lab for a bit, so thanks for that. I had no idea that their lab was basically a giant Faraday cage - apparently when you get that low in temperature things like electromagnetic power absorption from local radio stations or wifi routers becomes an important heat source. Nifty stuff. longview posted:If we need 60 liters of gas to surface a kg or two of negative mass then the weight of the container might be a deal breaker. A small compressed air cylinder like this one can hold 85 liters at atmospheric pressure, and you'd really only need to have blow out a ballast tank with a cubic foot or two of water to get ~10 pounds of buoyancy change. Set up your ballast tank with an air input port and a pressure release valve set to open at ~5psi differential, then manually fill it with water to sink the unit. Then have a solenoid set up to actively hold the secondary pressure regulator on the air tank output in the 'do not release air' position until your timer runs out or the battery dies. When the solenoid kicks off the ballast tank would blow out the water, and then eventually the compressed air as the unit ascends.
|
|
#
?
Jan 13, 2013 04:43
|
|
|
nobody- posted:Inductor/DC-DC converter question here, for you analog experts: Sure a handmade inductor can work, but pieces of ferrite/powdered iron can vary enormously in their permeability and frequency capabilities. So you should have at least a rough idea what the core's properties are.
|
|
#
?
Jan 13, 2013 07:46
|
|
|
ANIME AKBAR posted:Sure a handmade inductor can work, but pieces of ferrite/powdered iron can vary enormously in their permeability and frequency capabilities. So you should have at least a rough idea what the core's properties are. Ok, thanks! I used this guy's trick: http://dos4ever.com/inductor/inductor.html to get a rough measurement, and it looks like I can get about 15uH with four turns. I just got curious as most power supply inductors I've seen involve 10s to 100s of turns of thin copper wire around a cylindrical core, when it seems to me you'd get lower series resistance by using just a few turns of thick wire around a toroidal core.
|
|
#
?
Jan 13, 2013 18:10
|
|
|
nobody- posted:Ok, thanks! I used this guy's trick: http://dos4ever.com/inductor/inductor.html to get a rough measurement, and it looks like I can get about 15uH with four turns. Cost. Toroidal inductors are expensive. Tiny toroids are difficult to make via machine, while small cylindrical inductors are very easy. To wind a toroid, the entire length of wire has to go though the center hole. This is pretty easy if the center hole is large enough. This becomes a challenge to do quickly and requires lots of human intervention with a small hole. Using a large enough core to be machine wound on a small value inductor would substantially up the materials cost verses a tiny cylinder, as well as taking up board space.
|
|
#
?
Jan 13, 2013 19:27
|
|
|
|
| # ? May 9, 2024 07:58 |
|
|
longview posted:To make it ascend we'll probably drop some ballast using some kind of electromechanical system, none of this is set in stone yet and obviously the salt water makes everything more difficult but ideally we'd like a hook type thing that's held in place electrically, so that any battery failure makes it ascend automatically. I had the opportunity to play with Spray Gliders a bit along with a system that sounds a lot like yours. Both used similar systems to ascend and descend. The Spray Glider uses a screw drive to push oil from an internal bladder (inside the solid hull, so zero displacement) to an external bladder to change its buoyancy. It can also control its angle of attack by moving internal weights along screw drives and tracks to move forward or turn while ascending or descending. The other system (whose name escapes me) was a buoy that used the same principle to bob up and down and expose an antenna when it surfaced. It takes very little power to run the screw drive compared to most other solutions to this problem. I was surprised at it's effectiveness and would recommend you consider it; your problem sounds almost exactly like theirs, and this is the solution WHOI settled on.
|
|
#
?
Jan 13, 2013 19:49
|
|