![[info]](http://l-stat.livejournal.com/img/userinfo.gif){kind=small}
exiledbear's journalLog in Create a LiveJournal Account Learn more
| You are viewing exiledbear's journal Log in Create a LiveJournal Account Learn more | Explore LJ: Life Entertainment Music Culture News & Politics Technology |
exiledbearRecent Entries | ||
|
|
You are viewing the most recent 20 entries November 20th, 2009: And you wonder why I haven't upgraded to Karmic http://linuxhaters.blogspot.com/200 Sometimes change you can believe in, doesn't mean it's good change... : Sigh I think I'll add some more black boxes to the next revision of the charge controller design. I've got a PCB on order, so this is the equivalent of a code freeze and branch. First black box - a PWM generator than can pump out a higher frequency. The size of the inductor goes as the inverse of the frequency. I've got that arduino going as fast as it can (61.25kHz), and that inductor is huge. I'd like to be able to cannibalize inductors from old computers and other junk electronics. Of course, that would mean a DAC or something cheesy like feeding the arduino PWM -> voltage smoother -> PWM generator -> switch, but I think the smaller inductor will make it worthwhile. I've seen what size inductors you can get away with at 500kHz, and they are a LOT smaller, even when rated at high current. Second black box - high side MOSFET gate driver. n-channel MOSFETs are somewhat cheaper and lot more common and available than p-channels are. As crappy as it is to work with them on the high side, I think it's probably a good long term thing to prefer them over p-channels. : I don't think I ever showed you the furnace fan control unit  I just completed some major upgrades to it - it wasn't quite stable before. The power supplies to the arduino and the relay have been beefed up, and I added a hysteresis loop in the control code to stabilize switch offs. I think at some point, I'll lay out a schematic and make a PCB for it, but it works as it is. May use batchpcb.com for this one, although I hate doing business with the Chinese. : Waxing cynical for a moment here http://www.nytimes.com/interactive/2 Yeah, I know, hard for me to do. Must hold back. If someone comes up with a religion that isn't too wierd, non-demanding, and easy to join but substantial enough to be taken seriously AND rejects health insurance as a mandate, I suspect that religion might become popular. Or heck, if I was running a kooky cult of any kind, and I was hungry for new members. I'd put that in my religion right now. And start using it as a selling point. November 19th, 2009: Yes! http://www.mcclatchydc.com/251/story/79 Now let's work on the other 49 states. Marriage should be illegal. Everyone is shacked up. : And it takes a while to get them back too once lost http://thearchdruidreport.blogspot.c When civilizations come unglued, in turn, all these indirect subsidies for economic centralization go away. Roads are no longer maintained, harbors silt up, bandits infest the countryside, migrant nations invade and carve out chunks of territory for their own, and so on. Centralization stops being profitable, because the indirect subsidies that make it profitable aren’t there any more. ... The resulting race to the bottom, in a small enough market, might end with nobody able to make a living as a blacksmith at all. You don't say. November 18th, 2009: Sailing on the high side  The left side of the breadboard has gotten a little more complicated, but not too much more. The n-channel is now a p-channel and it's sitting on the high side of the circuit. The p-channel isn't quite as beefy as the n-channel I got, but it's beefy enough - 100V at 16A or something like that. I don't think you'd want to try to run it at those limits, but at 50% capacity, that's 8A, which is what I'm shooting for. The voltage doesn't really matter too much, it's current that drives out the magic smoke. One pull-up resistor to hold source and gate at the same voltage level and a NPN BJT to sink gate to ~5V when the PWM pin pulses. That should allow the MOSFET to switch over the region I care about, gate has to be 5V below source, and that makes the minimum switchable voltage 10V or so. Below that, it shuts off, which is a nice failure mode, at least to me. I'm not sure about how it fails at the other extreme, these things supposedly have a tendency to latch up. I'll have to look at the datasheet. I suppose if I really wanted to, I can put a resistor in front of base on the NPN and lower it somewhat, maybe to 1 or 2V. Again, I don't really have a good test load to throw at it (without risking more magic smoke), but the voltage at the output responds to wider pulses with higher voltage. I think I can simplify the schematic a little after seeing how the critters all behave together, and then I'm back to deciding whether to go for a lead-acid battery or try to fake it out. And whether to go for a PCB or not as well. November 17th, 2009: Leave it to the Germans http://gajitz.com/morphing-material-kee I suppose all of europe has a precision fetish, but the epicenter is in Germany, for sure. I remember the beer - Dutch and Belgian beer would have a recommended temperature range. German beer had a temperature REQUIREMENT. It's the little things you notice that tell you about a people. Beer glasses have volume marks on the side, set at precisely 500ml. No more, no less. Washing machines don't have ambiguous settings like "hot" or "warm" or "cold". Oh no. That would be an affront to sensibility. They have settings like 90C, 70C, 50C, 30C. I'll leave it to you to figure out which ones mean which. Whether or not the washing machine actually honors the requested temperature is another matter, I'll leave alone. I'm sure that someone is constantly busy with a thermometer, to do the verification and send in the complaints. It is an interesting concept. They've invented a "thermal capacitor" basically. Dunno, if I care enough to ever get one, but interesting, yes. November 16th, 2009: No, that's OK, you can renege on your promise I won't mind. Not at all. No, don't do it. Nooooooooooooooooooooooooooooooooooooooo : Adventures in thru-hole soldering  I need to get a smaller iron tip. And a table lamp. And one of those magnifying glasses. If you do much soldering you start to want one of those. This is an assembled kit that follows the arduino standard. It's 100% thru-hole components. It has two less LEDs than the "official" arduino, and it doesn't do USB at all. But that's no problem - I have a USB to RS232 dongle laying about, and it works just fine with it. It's somewhat cheaper than the USB version, but the nice feature I like about it is that you can program it while it's hooked up to an external power supply. The other style, you have to program it, detach it from USB and then hook it up to your external circuits. And now I have a backup (or main) in case of another magic smoke event. : Hmm, charge pumps aren't that bad http://www.edn.com/contents/images/3218 I actually understand this schematic, and why everything is where it is. The basic principle is to put capacitors initially in parallel and then switch them in series. It's slightly tacky - it actually inverts the waveform, because those are PNP BJTs, but I can understand why he's using PNP's. Oh yes. He doesn't care - because he's dealing with a 50/50 duty cycle. For me, inverting a PWM pin means that the max value becomes zero and zero becomes the max value. Annoying but manageable. I think the RC values would have to be retuned as well. Not sure what frequency he's tuned this for. I dunno. The pMOSFETs are still more straightforward. : I should add Colorado Springs in there From Colorado Springs to Boulder to Littleton to Granby to Longmont to (now) Fort Collins, welcome to Colorado. Watch your back. November 14th, 2009: Take a walk on the high side Grr. nMOSFETs are really really annoying to use on the high side. Charge pumps, push-pull arrays, level lifters, and none of those things are trivial. Just on charge pumps alone, try it - do a Google search. People are patenting shit on that stuff, if they're not writing academic papers on it. There are people out there and that's all they do. Someone wakes up in the morning and says, I need to build a better charge pump. Must build a charge pump for my thesis advisor. pMOSFETs aren't quite as annoying, but not straightforward either. To get it to switch, you still need something that will sink to ground and you probably need a pull-up resistor to keep the gate stable. But still, it's a circuit I can visualize in my head, and a schematic that does not look hilarious. One of the design goals of this thing, is to keep the number of integrated components to a minimum. The only real black box in this whole thing should be the Atmega chip - and everything else should be widely available. I don't want to put another black box in the design, like a charge pump chip. You know, people publish these theoretical schematics, and you see a switch there, and there's some handwaving, and presto, this is how it works, and then you go and try to build something that actually does work, and nobody, and I mean nobody says something like "Oh, and if you're gonna switch something on the high side, you might want to use a pMOSFET and control the gate with a BJT and a pull-up resistor". Something that would've been really helpful to know. |
|
