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If anyone wants a good small project to begin on, try the Mintyboost. It's a great, simple project that only costs $30 and is a good introduction to soldering.
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Jan 9, 2008 05:19
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Hillridge posted:Don't scratch your face while holding the iron. I got a nice burn on my nose from doing that. Also, don't solder barefoot. One drip on your foot and you learn that lesson. Jesus christ, I don't think I could ever mentally get a soldering iron near my face. The first burn I ever got was the result of a surface mount resistor getting stuck to the tip of my iron. Tried wiping that off with my hand, heard sizzle, realized hand was burning, ouch. It was kind of cool though, because I found out that you can use a soldering iron to remove your fingerprints (at least for a month or so).
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Jan 9, 2008 18:38
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So I finally have a working theremin built from this site. Right now I have it working through an AM radio, but I need to hook it up to an amplifier to get it through a speaker so I can also have volume control. Would that be something I could just build, or something that I would need to purchase?
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Aug 19, 2008 02:34
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If you need to get good at soldering just join a research group that requires 5000 0402 sized surface mount components replaced. My hands are fairly shaky but after that summer I was able to solder a flea's dick to ant's oval office. It's a zen experience. No lie, I've killed a fly in midair by swiping it with the tip of a hot soldering iron.
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Jun 28, 2009 06:04
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Is there anything I should keep in mind when designing a system that has to accurately transmit signals up to around 100kHz? I'm trying to implement a system that's meant to measure high frequency noise signals in a cryogenic environment. I'm pretty confident about most of the details, but I'm trying to see ahead of time if there's going to be any problems related to the high-frequency part of it. Everything past the breakout box part has to fit in a tube approximately the diameter of a soda can, so space is a premium. 1) Breakout Box - Box that I plug my instruments into that leads down into the belly of the cryostat. They attach through BNC connectors, and here's where I'll have low-pass pi filters installed to help stop outside electronic noise from getting to my samples. 2) Transmission lines - I'm going to be using Thermocoax cabling as my transmission lines. Thermocoax cables are designed to be used as heating elements, but they also act as high frequency filters due to their small size which causes losses from the skin effect. The pi filters get rid of noise up to around 1GHz, but due to parasitic inductances you get spikes in the filtering above that. The thermocoax cables don't start attenuating until around 1GHz, but they're pretty effective after that. There's going to be 6-8 of these lines but they're pretty small so space shouldn't be an issue. 3) Connection to sample holder - I have to solder the wires to some kind of connector that attaches to my sample holder. The connection has to be removable, as the sample holder can be switched, so the connections have to be able to plug in and out. This will be attached to a PCB (that I'll have to design) that I plug my sample into. I'm slightly unsure about how I should attach these wires to the sample holder - our current set-up has 20 wires soldered into a plug, but it's just plain copper wiring and doesn't carry high frequency signals. I've heard of other labs using SMA connectors, but I'm wondering what is necessary in order to keep the integrity of the signal intact. How important is the connector when maintaining the integrity of the signal? What type of connector should I be looking for that does not affect high frequency signals? 4) Sample holder - PCB attached to a machined piece of copper which has a small holder in which we plug in our samples. This is small, on the scale of a credit card or two. The signal lines go to the place where we plug our sample into, which then goes through connectors we made with a wirebonder to our actual devices under study. Anything I should keep in mind when laying out the PCB for this?
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Jan 7, 2013 21:16
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sixide posted:I'm not a cryogenics expert but I know a thing or two about coaxial components. If you are only going to 100 kHz, you have basically nothing to worry about electrically. Focus on the mechanical challenges. Ok, I have a much better idea on what I'm doing now.  Here's a general overview of what I'm doing. There's a problem, though: Thermocoax: Here's a pdf with another group who did something similar to what I want to do. The main difference is they solder the sample end of their wire directly into the chip holder, while I have mine go into SMA connectors (because my sample holder has to be detachable). My problem is on the other end, where they have to somehow go from vacuum to atmosphere, and preferably through a connector (so I could take off the breakout box if something in it needed to be adjusted). Our current set-up uses Fischer connectors mounted through a vacuum sealed port (picture here). Is there a way to have something similar to this with coaxial cables? Or should I do something like this, where the coaxial cables go straight through? And maybe I have SMA connectors on the other end outside of the epoxy, and screw them into my breakout box? I'd basically be building my own connector, at that point. Still thinking this out. Any ideas?
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Jan 9, 2013 21:51
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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.
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Jan 11, 2013 23:48
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sixide posted:Anything other than SMA or BNC will hit your pocketbook, but I'd look at SSMA/C for tiny threaded connectors and MCX/MMCX for snap-on. SnoPuppy posted: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. PDP-1 posted: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. Thanks for the help, y'all! I'm considering two set-ups now: 1) The transmission lines all separate from being closely packed on the way down into the cryostat into their own floating MMCX jack at the bottom of the fridge (like peeling a twizzler), which I can then individually connector to the corresponding plug from the sample holder. After all the connections are made, I tape down the wires to mechanically secure them. 2) A DE-15 connector, with half of the connections as ground to help shield the signal lines from each other. I found one laying around in our lab:  And I was thinking about doing something like this:  I+ and I- lines just carry DC signals. I'm only likely going to be using 6 of 8 of the pins at once, so another two of those lines will be grounded (the entire system is going to share a common ground). The most important thing is that V+(-)2 and V+(-)1 have minimal crosstalk. I'm doing a cross-correlation measurement between the two of them, so they need to be as independent as possible. Will some grounding pattern like this actually help at all? Outside of this connection, the wires are going to be coaxial until they get to the sample holder. I don't know if I've mentioned this yet, but all of this is contained in a pretty thick copper sheath that acts as our vacuum chamber/faraday cage, so we don't have to worry too much about outside noise. It's mostly the inter-transmission-line noise that I'm concerned about.
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Jan 17, 2013 23:17
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| # ¿ May 3, 2024 18:53 |
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SnoPuppy posted:MMCX is going to have the best SI and isolation, but the DE-15 won't be bad either. Cool. V+1/V-1 are indeed halves of a differential pair. What do you mean by "connections to the connector are coax"? For DE-15, it's basically a choice between solder and crimp connections. And all of these connectors will be totally contained in vacuum, so there's no worry about vacuum sealing.
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Jan 18, 2013 20:01
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