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I'll just post a picture: Those hose segments effect the grounding, I think they're pieces of filter-line actually but they were the right size to press against the lid (I just super-glued them on top of the PCB).  This is the response with the extra grounding, it's "adequate" but a bit rough above 2 GHz (not a huge deal right now). The resonance was at 2.5 GHz. Plot is reading gain offset by 30 dB so the 0 dB is 30 dB gain. The preamp is nominally a ~100-3500 MHz 30-40 dB low-ish noise amplifier (around 2-3 dB NF). The amplifiers are ADL5610s (selected for suitable OIP3, P1db, and relatively flat gain). Amp bandwidth is set by some LFCN-3000 filters at the input/output. The output splitter is there since the box was a 3-port box already, so might as well use that port. This thing is designed as a laser diode driver (hence the high gain, and need for moderately precise P1db). Total flatness is not a huge deal, since the idea is to channelize multiple receiver antennas onto one link with sharp band pass filters, and apply separate AGC per antenna band. That way it's basically irrelevant if the gain at 400 MHz is not the same as the 1.5 GHz gain, since they have separate AGC amps. What is a problem is when there's a narrow 10 dB spike in the middle of the spectrum, hence the need to dampen that out. For now I haven't designed those AGC amps, but they will be in a larger box with similar construction, so I expect the resonant frequency to go down around 2x. So far I have a demo setup with 400 MHz and 1.2-1.6 GHz (GNSS + L-band services) antennas feeding the laser, and a passive PIN detector is able to detect the signal with no loss of sensitivity compared to a direct hookup! Those PIN detectors aren't entirely flat either, so the AGC adjustment for a flat response (e.g. equal noise floor in all bands) will be referred to the optical detectors, not the intermediate RF stages.
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Apr 1, 2021 12:14
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Huh, if the black cylinders don't conduct electricity, then I think they are just acting like RF absorber material. I don't know what filter-line is. Maybe just wallpapering the enclosure with absorber (sometimes it comes with adhesive, and you can apply it to surfaces like a sticker) will help you. If your RF lab has brick ferrite absorber, you can try loading the enclosure with that, especially in the vicinity of the 3 amps. I've never used an EMI test receiver, so I guess I don't know what to expect but I see periodic spikes with height of multiple dB in your gain plot. Are those an artifact of the measurement? Are you testing through a long length of cable which, when combined with a bad port match, would create the ripple? If not, that's a little worrying, if you are just measuring transmission through a limiter, 2 filters, 2 attenuators, 3 amps, and a power splitter (I think, from the photo), nothing there should be creating such sharp response with frequency. Are you getting the power gain you expect to see? Do you see the spikes when you test with the lid off? When you turn the power on to the device and and do not excite it with the RF signal source, do you see tones self-generated by the circuit, when you connect the output to a spectrum analyzer, with lid on/off? silence_kit fucked around with this message at 13:03 on Apr 1, 2021 |
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Apr 1, 2021 12:45
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The receiver is operating in spectrum analyzer mode for that picture, it's just a software package + some extra EMI filter options for the detector that differentiates it from a spectrum analyzer. The amp is not oscillating (I don't think it was actually oscillating before I dampened the resonance either but don't recall if I checked specifically for that). Those little ripple are presumably caused by an impedance mismatch, it's probably either component pad geometries being wrong, or (more likely) that the nominal trace impedance is off. I set the trace parameters up using AppCAD and the nominal parameters of the PCB process I was using, and it's not shocking if the actual results are a bit off. Could also be the pi-attenuators between the amps are too chonky for those frequencies (I'll probably buy attenuator-packages from Mini-Circuits next time). For now at least this is Good Enough for my purposes, but I'll probably investigate it further before designing more boards for the project and try to do better next time. I do have a nanoVNA v2 that can operate in TDR mode with not terrible resolution so might be able to see the transmission lines and get a reading of what the actual impedance is.
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Apr 1, 2021 13:03
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longview posted:Could also be the pi-attenuators between the amps are too chonky for those frequencies (I'll probably buy attenuator-packages from Mini-Circuits next time). You are right--your attenuators are probably not working like how you expect them to work past ~250-500 MHz or so. To accurately design RF lumped element circuits above this frequency range with this technology, you need to co-design the layout with the lumped element components, and absorb component parasitics into the circuit. But I don't think this would create such tightly spaced ripple with frequency in the measurement. The attenuators and the connections to and from them, aren't electrically large/long enough. I feel like maybe you are measuring through a cable which is not being calibrated out, and the match the box presents to the cable is not good, and this might be creating ripple, assuming that the circuit is not oscillating and that the ripple is not an artifact of the measurement system. I feel like there is nothing in the box which would create ripple that tightly spaced with frequency--I think your circuit is not electrically large enough. silence_kit fucked around with this message at 13:19 on Apr 1, 2021 |
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Apr 1, 2021 13:15
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I checked some of the pictures and I did swap cables at one point during the measurements. I definitely calibrated them for transmission losses, but the first set of cables (RG-316 double shielded) showed fewer ripples in the same setup. The picture I posted used some kind of triple shielded expensive test cables. Both cable sets were in the 1.5-2 m range. Using my DSA-815 I don't see any significant ripples (limited to 1.5 GHz), so could be a measurement issue. I checked gain both with a tracking generator and a signal generator, and gain was always as expected and no unexpected artifacts were found. I had a 70 dB step attenuator in series for all these tests tests (I calibrated at the 0 dB setting then connected the amp and attenuated; could be a source of error?). I'm not too worried about it, if I see ripples when I start running actual signals through it I'll have to investigate further (and worst case do a respin), but I'm doing this for fun so not planning on doing a root cause analysis here 
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Apr 1, 2021 13:53
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longview posted:I checked some of the pictures and I did swap cables at one point during the measurements. I definitely calibrated them for transmission losses, but the first set of cables (RG-316 double shielded) showed fewer ripples in the same setup. The picture I posted used some kind of triple shielded expensive test cables. Both cable sets were in the 1.5-2 m range. It isn't a scalar loss effect, it is a vector effect, and I got it wrong in the earlier post. If your cable surge/characteristic impedance at the output of your device is perfectly matched to the system impedance and if the next device is well-matched to the impedance level, the match presented to the output of your device and cascaded scalar match level will not change, and so will not create gain ripple, even if your device is not well-matched to the system impedance level. However, if your cable is not well matched, or if the next device is not well-matched, the effect of adding the cable between the two devices will add ripple to the gain measurement if your device is not well-matched to the system impedance level. The bad cable will either warp the match presented to the output of your device or the cable, even if it has perfect characteristic/surge impedance value, will rotate in phase the impedance presented to the output of your device, and depending on whether there is phase cancellation (example: series inductor + shunt capacitor can create a 'match phase cancellation', and in this way, you can create a good match by combining two poorly matched components), will make the match good or bad. In either case if the cable is electrically long, then the gain ripple can be tightly spaced in frequency. If the cable is electrically short, the gain ripple is not very tightly spaced. This is why I don't think the connections inside of your box is creating this effect, because they aren’t electrically long enough. Does this make sense? longview posted:I'm not too worried about it, if I see ripples when I start running actual signals through it I'll have to investigate further (and worst case do a respin), but I'm doing this for fun so not planning on doing a root cause analysis here You should be striving to achieve RF Perfection at all times! 
silence_kit fucked around with this message at 14:58 on Apr 1, 2021 |
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Apr 1, 2021 14:34
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Stack Machine posted:Have photos (or links/model number) by any chance? I'm super into the "densely packed forest of oversized components" aesthetic. i was wrong about this, btw, i was conflating legit cordwood assembly with just stacking multiple discretely-assembled modern PCBs via unsoldered pin-socket couples. Similar layout done for the same reasons, but trivial to fabricate and with none of the retro charm. If/when I revisit my surveillance bug scratch-builds and take them off the breadboard, I do want to attempt the traditional very compact assembly style that doesn’t use off-the-shelf protoboard, so sth in the neighbourhood of a cordwood build is likely. Ambrose Burnside fucked around with this message at 20:50 on Apr 1, 2021 |
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Apr 1, 2021 20:36
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That's different from what I thought you meant. I was reading "additional lid-ground points" as meaning connecting the lid and box at closer spacing with extra screws or something
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Apr 1, 2021 21:58
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I’m looking for a small solar panel, like 2x4in, to fit inside a case. The dimensions are pretty tight. Is there a “custom fit” panel that would work, or like a ‘cut to fit’ thin-film panel?
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Apr 2, 2021 07:07
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Browse AliExpress for some nice sized ones? That seems like it should be an extremely common size. Keep in mind you can serial/parallel a bunch to jigsaw your ideal panel
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Apr 2, 2021 07:26
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If you find one on aliexpress, don't forget to check if it's on amazon or something. You'll pay more, but you'll also get it sooner than waiting 3 weeks for the slow boat from China.
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Apr 2, 2021 07:39
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PRADA SLUT posted:I’m looking for a small solar panel, like 2x4in, to fit inside a case. The dimensions are pretty tight. Is there a “custom fit” panel that would work, or like a ‘cut to fit’ thin-film panel? Goldmine has these pretty cheap right now, $9 for 3.85" x 6.5" x 0.37" outputting "5.5VDC and 0.360Amp (about 2 Watts)" to a USB port: https://www.goldmine-elec-products.com/prodinfo.asp?number=G23903
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Apr 4, 2021 02:02
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Stack Machine posted:Well it's a shame that it didn't work but there is so much that could be going on there in the original product. So funny story. Short recap: tried to build an arcade stick out of a game pad. Ended up with all kinds of wacky input issues. Update: got the new controllers in. Better pcb than the first one however, it had wipers like the first one (just engineered differently) and yet again, the solder point with one of those ended up breaking off. I ended up doing a way nicer job resoldering it and attaching to points on the traces. Plugged it into the windows game pad indicator and... got the exact same errors at the last one. So I took a breath and plugged it into the system - and there was only a couple of small issues. The left input was always on, and three of the buttons didn’t work. I desoldered those buttons and could find that the left input had in fact been bridged with a tiny point of solder. Fixed that easy enough. The other ones I could see that I didn’t have a great contact and there were points where the traces on the pcb were rubbed / burned off. So I found new attachment points and just sucked up the burning in my fingers when the wires heated up. After 2-3 hours of moving back and forth to test and reheat the irons it worked. Moral of the story: test often but know that sometimes the input data that you see is not accurate. Yay! We did it, EE goons!
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Apr 5, 2021 01:42
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Not sure if this is the correct thread for this kind of question. If so, apologies, and I'll gently caress right off to another thread if I need to. I'm building a lightsaber and I was wondering if I could make it charge wirelessly, and ideally, horizontal rather than vertical like a toothbrush. My idea is to buy the strongest wireless charging base within my budget, build it into a saber mount like this:  and dismantle one of these, and wrap it around the outside of the hilt like a hotdog bun, then wire it to the usb-c charger in the chassis of the hilt. Then just covering it up with a leather hilt wrap. Is this even feasible? Is there an example of this type of charging in the wild? I read that wireless chargers can't be bent like this or else they won't work. Is this just dumb or even possible to do? Thanks in advance goons way smarter than me. 
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Apr 5, 2021 08:10
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Wireless charging can be quite tricky. The geometry of the two coils does matter, and so does the distance between them. Even a few millimeters of separation can be enough to effectively kill the transmission. For that reason I'm not sure that wrapping the charging mat around the hilt would work correctly -- most of the receive coil would be too far away from the transmitter. Those vertical toothbrush chargers work by having one coil in the base of the toothbrush and another one surrounding it when it's placed in the charger. That's a very efficient geometry for power transmission. You could do the same thing with your lightsaber but you'd have to make a mount that it slides into sideways. If you just want it to charge when dropped into place, and you're building this lightsaber from scratch, maybe consider putting a pair of charging contacts on the outside of the hilt and just installing some pogo pins into the stand/holder? It's not technically wireless but it'll still charge without having to plug anything in.
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Apr 5, 2021 08:26
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pogo pins would be my suggestion as well but you'd have to be somewhat careful in how you design the shell to not short out the whole system, seeing as how the whole thing seems to be an aluminum housing.
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Apr 5, 2021 12:39
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Other options I see could be: a) If the main body is conductive, use a ring of plastic (or two) hidden along the body somewhere so that the two ends are insulated. Then whatever you hang it on could be two contacts that charge it through the main body. b) Use a toothbrush style charger at the very base, so that it sort of slides in/locks in place slightly at one and and then tips down the last 10-15 degrees at the top to sit horizontally. The bottom of the assembly around the toothbrush receiver would have to be plastic most likely. c) If you do use pogo pins consider magnetic alignment to position/hold it precisely in place. The supply should have current limiting of some kind so that if they accidentally get shorted against the body it powers itself off. Rescue Toaster fucked around with this message at 14:06 on Apr 5, 2021 |
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Apr 5, 2021 14:04
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What you want should be physically possible, but I have my doubts about your approach, and solving the problems may be outside of the capabilities of a hobbyist. First up: when it comes to antennas, yes, geometry is important. It's practically the whole ball game. So your hot dog idea may be doomed from the start. But my experience in this field is limited, so I'll allow you the hope that someone else could tell you that it might work with severely downgraded efficiency. Secondly: inverse square laws are a bitch. Even if your antenna shape is sound, wireless power transmission works better the smaller the gap. Wrapping a layer of leather on top of anything is likely to kill whatever efficiency you did have. Again, I'll caveat this that my exposure is with systems that need maximum efficiency, so it's possible it could still work, just at a level that would be unacceptable for a product. But thirdly: there's hope! Were you counting on an aesthetic that had a leather grip? Most lightsaber designs I've seen have had a lot of exposed metal, so it might be possible to design a charging system that uses actual exposed contacts that blend into the design. There would still be challenges, but they'd be far more surmountable.
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Apr 5, 2021 14:48
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Martytoof posted:pogo pins would be my suggestion as well but you'd have to be somewhat careful in how you design the shell to not short out the whole system, seeing as how the whole thing seems to be an aluminum housing. This was my thought too, pogo pins with some magnets to align it when you plop your saber on the stand. Same idea as the (old?) macbook power adapter connector
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Apr 5, 2021 16:52
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KnifeWrench posted:What you want should be physically possible, but I have my doubts about your approach, and solving the problems may be outside of the capabilities of a hobbyist. Yeah, if you need to visualize it, if you've ever used an induction range for cooking, that's the exact same idea. That's a LOT more energy than you need being transmitted in that case, but that application has pretty much the ideal physical geometry to work really well with inductive power transfer, namely that the interface is a really huge area and can be really close to each other (coil in the range, big chunk of metal to be heated in the bottom of the pan). Works really well for a stove top with pots and pans because the standard interface from the user's perspective doesn't really change to accommodate the induction heating implementation
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Apr 5, 2021 16:58
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Just have it connect to an external power supply and claim it's an early prototype jedi design where the kyber crystal had to be strapped to your back 
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Apr 5, 2021 18:17
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Martytoof posted:Just have it connect to an external power supply and claim it's an early prototype jedi design where the kyber crystal had to be strapped to your back I thought after you imbued the Kyber crystal with The Force during a meditation session, the lightsaber doesn’t need an external power source. Maybe that’s the problem? Just a thought for the OP.
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Apr 5, 2021 18:32
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I mean maybe in version 1.1 but who has all the kinks ironed out on day one?
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Apr 5, 2021 18:40
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An electric toothbrush style inductive mount where the charger and lightsaber are coaxial with the charger surrounding the handle would work okay if you don't need great efficiency, but you'd want to be doing the transfer at hundreds of KHz, so need to be building an inverter on the charger side and a rectifier on the lightsaber side, which may be more circuit design than you want. It's basically an air-core transformer with extra restrictions on where you can put steel to direct magnetic flux.
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Apr 5, 2021 19:17
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This thing probably spends 99% of its life sitting on the stand, right? How about just a solar cell and MPPT to trickle-charge it?
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Apr 5, 2021 20:13
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How much power do you need to transfer is the big limitation here. If you want to fast charge it during a day of hard use the wireless idea isn't going to work. But if you only need it to top up and maintain over 24hrs you can build a simple inefficient one and that'll be fine.
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Apr 5, 2021 20:17
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Holy crap thanks for all the advice everyone! I'm phone posting at the moment, so I'll see if I can answer some of the posed questions. It's going to be powered by a single 3.7v 3120mah 18650 battery. There is a charge port in the chassis to allow for direct charging, but that requires opening the hilt and plugging it in. My initial aim was to be able to charge the saber while it wasn't in use on the base, which would be able to be switched on and off so the battery isn't constantly being charged while stored. Now that I think more about it, I might want to have the ability to charge it while I'm away from home as well, requiring an external charge port. For the sake of simplicity, I might just design the mount to act like a wired charger with the connection protruding from the bracket, similar to how a phone case battery connects to a phone. Part of the reason for my initial desire to go totally wireless/no connectors was there is nothing like this in the lightsaber building community. Most people simply dismissed the idea out of hand in 2016 and never really looked back into it as far as I can tell. The Qi charging and other forms of wireless charging have advanced considerably since then, even allowing a charge through most organic materials, even so far as an inch away from the device, or through a wooden table. I hadn't considered a solar cell to charge it, that might be a fun on the go option depending on the cost of the cell itself. I could have the chassis displayed separately, and devise some kind of pogo pin/magnetic alignment as mentioned to charge it as well. Here's what the chassis looks like as a 3d render  I might be able to wire the charge port in a different place in order to be able to basically plug onto the mount, both displaying it and charging it, but I don't know if I'll be able to wire it in such a way that the chassis is removable from the hilt. The workable space on the chassis is at a premium as it's designed to not slide around when flipping the saber all over hell and back. You guys have given me a lot to consider and look into! Thank you so much for your insight. I'll post updates in here as I work on it to see what can be done and what cannot. 
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Apr 5, 2021 21:32
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i love this electronics thread because seriously why are electronics people everywhere else on the internet literally always assholes oh well obviously the guy posting on r/arduino has bought a discrete QFP neo-6m GPS chip not even mounted on a carrier board, definitely, no way would he have one of the 10,000 identical arduino-compatible serial neo-6m modules available for 10 bucks on amazon, better not make ANY assumptions here eat poo poo Sagebrush fucked around with this message at 01:52 on Apr 6, 2021 |
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Apr 6, 2021 01:49
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Yeah this and other threads in this subforum are phenomonal. The more technical SA threads are v high quality. Some parts of SA are filled with jerks too though.
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Apr 6, 2021 02:02
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The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Try to learn electronics while we laugh at your misadventures
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Apr 6, 2021 02:15
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I've been sending a note with the latest batch of RTD modules to the effect of "oops, the silscreen is hosed! MOSI is MISO and MISO is MOSI. And those instructions by the standalone jumper? Reverse them. Gtg now!
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Apr 6, 2021 02:29
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silence_kit posted:I thought after you imbued the Kyber crystal with The Force during a meditation session, the lightsaber doesn’t need an external power source. Maybe that’s the problem? Just a thought for the OP. From what I understand about crystal charging, “meditation” is an interesting choice of phrasing for the process.
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Apr 6, 2021 02:32
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I guess that's a real knowledge vs wisdom kind of thing. Knowledge is knowing that the neo-6m doesn't have a battery backup, it has an input for one. Wisdom is figuring out that the guy bought a module from the internet and whatever he bought likely has a battery on it.
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Apr 6, 2021 02:53
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I mean yes, but mostly it's just being deliberately dense to show off how much smarter you are than the guy asking the question. Oh dohohohohoo here's a technically correct answer that doesn't give any useful information, I know exactly what you're really asking but I'm going to gatekeep it until you figure out how to play by my stupid rules. Every community I'm part of (motorcycles, electronics, aviation, machine shop stuff, etc) has its lovely grognards who do that poo poo to every newbie and then complain that no young people are interested in the hobby.
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Apr 6, 2021 03:19
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Yeah there are some communities that you learn by counterexample to just never ask questions, but the topic subforums of SA have always been different somehow. Hell I joined way back in 2003 because I couldn’t figure some computer thing out and a friend recommended I try asking in SH/SC. Well done goons
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Apr 6, 2021 03:43
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I've built a project around one of the NEO chips (though it's from the 8 series, I can't imagine they made the power consumption much better between them) and a CR2032 has lasted like 4 years so far and is still fine. It's just there to power the NVRAM to keep warm start data so the thing doesn't have to do a full GPS cold start so it lasts as much as like, a CMOS battery would. ... if anyone was curious.
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Apr 6, 2021 04:03
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It's because these forums are dead and gay. The NetBSD community is the same way  (seriously though, it's really awesome here!)
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Apr 6, 2021 04:48
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What do you make the pogo pins poke in an application like that anyway?
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Apr 6, 2021 07:24
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Dominoes posted:I've been sending a note with the latest batch of RTD modules to the effect of "oops, the silscreen is hosed! MOSI is MISO and MISO is MOSI. And those instructions by the standalone jumper? Reverse them. Gtg now! If you swap TX/RX every time, it's still a 50/50 shot if it being right. (vs. 0% if you don't  )
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Apr 6, 2021 08:00
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SchnorkIes posted:What do you make the pogo pins poke in an application like that anyway? Pogo pin receptacle 
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Apr 6, 2021 08:13
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