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Bad Munki posted:Since I'd literally never even looked, I didn't realize inductance/capacitance meters were so reasonably priced. Is something like this probably going to be good enough for hobbyist purposes? The attempt to blatantly copy fluke is a turnoff.
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Feb 14, 2014 02:55
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It was literally the first product that showed up when I searched for "inductance meter," whatever. Any recommendations in, say, the less than $80 range? No real specific requirements, I just want something that'll be generally useful and reliable. Off the top of my head, one project I'm working on now I need to measure inductance around 30uH, but I don't know what else right now.
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Feb 14, 2014 03:44
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I think the australian guy (eevblog?) did a review of cheap inductance and capacitance meters as part of his series of reviews of cheap dmms
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Feb 14, 2014 03:50
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Thanks, I'll check it out.
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Feb 14, 2014 03:55
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So I'm trying to build myself a little desktop coil gun. Really simple, not especially dangerous*, just a couple of photo-flash capacitors and a heavy coil around a plastic tube. Put a piece of steel wire in the tube, close the switch (though I'm thinking of a high current SCR or something instead) and watch it go poink. I'm currently charging up the capacitors (330v, 180uF) using the original circuit ripped out of a disposable camera and I love the rising whistle it makes as it charges up. However, it's kind of slow to reach full power and gets slower and hotter as I add more capacitors. This isn't exactly what I have, but the circuit appears to be very similar:  Not all of it is directly relevant to my application. For instance the whole thing with T2 is just to pre-ionize the flash tube, I think, and that could be removed without affecting the noise or the capacitor-charging function. Right? Can someone explain (1) how this type of charging circuit turns 1.5v from a AA into 330v, because I think I get the gist but am still a little lost, (2) what part exactly is making the awesome whistling noise and (3) generally how could I beef up the circuit for more power but ensure that it still makes the same sound? *kinetically, I mean. The electricity is obviously enough to kill if you're unlucky.
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Feb 15, 2014 08:20
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Sagebrush posted:Can someone explain (1) how this type of charging circuit turns 1.5v from a AA into 330v, because I think I get the gist but am still a little lost, (2) what part exactly is making the awesome whistling noise and (3) generally how could I beef up the circuit for more power but ensure that it still makes the same sound? Background: Transformers turn a current in a wire into a current in a second wire via a magnetic field. The wires are wrapped in coils around a small circle, or bar, of iron. When you run a current in one wire, it creates a magnetic field in the iron, and that magnetic field travels through the iron, forcing current to appear on the other wire. If both windings have the same number of coils, they'll have the same voltage in and out; if there's a different number of coils, though, then the output will have higher or lower voltage, but lower current. The trick to a transformer is that magnetic effects only occur when the voltage/current on the wire changes -- it doesn't do anything if you just run a steady current through it. So, how does this circuit work? This circuit is actually somewhat unusual, because it uses a single winding for the secondary instead of the traditional feedback winding, and it makes describing the whole circuit a little tricky. When you press S1, two things happen at once with the current flowing through S1/R1: * C1 gets charged up. * Q2 gets activated; that current flow activates Q3 as well, which starts a burst of current flowing through the primary winding of T1. That, in turn, causes a VERY brief burst of ~330V to appear on the secondary winding of T1. Notice that the "positive" end of the secondary is connected to Q2/Q3 as well! The burst of high voltage on T1's secondary is going to cause Q2/Q3 to shut off. C1 then discharges, which reactivates Q2/Q3, causing another burst of energy, which repeats the process. So, Q2/Q3 are turning on and off very rapidly, which causes a wavering low-voltage input on T1, which causes a wavering high-voltage output on T1. This flows through D1 (a rectifier diode) and charges the big energy-storage capacitor, C2. The whining sound that you're hearing is coming from the transformer T1; when it's energized, the iron and wire slightly moves due to the magnetic forces in motion. (This is called magnetostriction.) The constant on/off pattern of T1 results in them vibrating, which you percieve as sound. As for why the sound goes up in pitch as the circuit charges: the design of this circuit has the property that the frequency of Q2/Q3 switching will increase as the voltage on C2 grows. For most of these circuits, they start switching at about 5KHz, and stop at around 11KHz. Now, if this were the only part of the circuit, this charging process would go on forever, and C2 would get dangerously charged. The combination of the NE charge light + R2 + D2 + Q1 is how the circuit stops charging: Q1 is a PNP transistor, and D2 is a Zener diode with a high breakdown. When the circuit has a low charge, the neon lamp doesn't conduct any current, so R3 has no current, and D2/Q1 are pulled to ground. As the circuit charges, around 200V or so, the gas in NE is going to ionize and start conducting (and lighting up). This results in current flowing across R3 and creating a voltage drop. Once it hits ~300V or so, the voltage drop across R3 is going to be bigger than the zener breakdown voltage for D2. This means that Q1 activates, C1 is drained, and the voltage inverter stops running. And yes, you could in theory remove the S2/T2 part of the circuit. The trick with Xenon is that it needs a very high voltage to initially ionize, but once it's ionized, you can dump energy through it at much lower voltages. So, when it's charged, the Xenon gas is fully exposed to the ~300V, but that's not enough to make it light up. S2/T2 form another small transformer circuit, just without the oscillation transistors. When you hit S2, it causes a small burst of current (at 300V) to travel through R3 and into T2's primary. This causes a very brief burst of 4000-5000V to appear on the output, which is enough to ionize the xenon; now that it's ionized, the entire stored energy can travel through the Xenon at 300V, and flash.
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Feb 15, 2014 23:03
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Sagebrush posted:So I'm trying to build myself a little desktop coil gun. Really simple, not especially dangerous*, just a couple of photo-flash capacitors and a heavy coil around a plastic tube. Put a piece of steel wire in the tube, close the switch (though I'm thinking of a high current SCR or something instead) and watch it go poink. I'm currently charging up the capacitors (330v, 180uF) using the original circuit ripped out of a disposable camera and I love the rising whistle it makes as it charges up. However, it's kind of slow to reach full power and gets slower and hotter as I add more capacitors. I made one of these before. Use a mcdonalds soda straw and a small plastic thread bobbin with 24 awg wire. It shoots BBs about 80 feet.
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Feb 16, 2014 07:49
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Sagebrush posted:I love the rising whistle it makes as it charges up. However, it's kind of slow to reach full power and gets slower and hotter as I add more capacitors. Back in elementary school a kid would always take these charging circuits out of the cameras and use them as a type of taser. That sound probably instills fear into people who I used to know. I just got some boards back from OSHPark that I think are pretty cool. I always wanted to get PCBs made up, but I usually make a mess of perfboard and put it in a project box anyway. This is probably the 10th board I've done layout and routing for that I've had produced. The intent for this thing is to turn the project into a Kickstarter, but we're still working on a library to make it way easier to work with if you're using an Arduino. 
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Feb 17, 2014 09:15
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UberVexer posted:I just got some boards back from OSHPark that I think are pretty cool. I always wanted to get PCBs made up, but I usually make a mess of perfboard and put it in a project box anyway. This is probably the 10th board I've done layout and routing for that I've had produced. Neat, but what does that... RJ45 connector on a board do?
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Feb 17, 2014 18:48
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I imagine it has SMD components on the bottom that do the thing the thing is meant to do but he's deliberately keeping them a secret 
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Feb 17, 2014 18:51
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Sagebrush posted:I imagine it has SMD components on the bottom that do the thing the thing is meant to do but he's deliberately keeping them a secret Maybe he's going to bitbang ethernet?
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Feb 17, 2014 18:58
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Parallel Paraplegic posted:Neat, but what does that... RJ45 connector on a board do? That RJ-45 connector plugs into an Arduino shield I had made also, it brings i2c and some analog pins over any straight cat-5 cable. Sagebrush posted:I imagine it has SMD components on the bottom that do the thing the thing is meant to do but he's deliberately keeping them a secret It's all going to be OSHW pretty soon. I'm big on sharing design documents. The entire board is SMD on the back side, yes. It's main purpose is to make development of accessibility gaming controllers easier and much more cost effective. I've worked with people who needed special controllers built out for different games, Call of Duty plays differently than whatever sports game is out at the time, so the guy had something like 3 custom controllers built out and they aren't really cheap. He asked if I could make a one handed MLB controller, so I did, but instead of ripping a controller apart, cutting the pcbs and rewiring the whole thing like anyone normally would, I just built on top of a software library for Arduino that allows communication as a video game controller. The small PCB I posted before is to be embedded inside of a controller, and is about 20 dollars, that plugs into the shield I mentioned before and then you've got an entire accessibility controller system for something like 60 dollars. For every controller after that, the person making the controller won't be taking apart a new controller, but putting in a 20 dollar PCB with standard headers or solder points. My real hope for this project is that a hakerspace picks it up and makes a bunch of controllers for people for basically nothing. I'm going to offer hackerspaces pretty big discounts. I also think that as 3d printing and whatever other home manufacturing technology gets bigger, people would be making things like FIFA controllers that you kick to shoot, or Train Simulator controllers that look like a real train, or whatever people would want. I'm trying to solidify how exactly I could get them made in Kickstarter volume without getting charged a ton of money. Getting the PCBs made up is all figured out already, and having the entire thing made in America is big to me  , so I was thinking of building up a small pick and place machine, as there are only about 5 unique components on the board and I like building robots that do my jobs... or I could just pay some engineering students to help.
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Feb 18, 2014 03:25
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Oh neat, that's a pretty feel-good project right there, I'd give to that kickstarter 
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Feb 18, 2014 03:54
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Parallel Paraplegic posted:Oh neat, that's a pretty feel-good project right there, I'd give to that kickstarter I think I've gained access to a pick and place machine from a university's engineering department, which means I just need to make a video that isn't terrible and I'll be ready to go. I'm really hoping it actually succeeds and I can make a bunch of boards for people. I just finished up some code that allows for different modes based on pin status, so you could theoretically have switches connected to the Arduino itself to toggle different features like rapid fire, or having like 3 'x' buttons, or functions that do multiple actions on a timer without the need to reflash the base module all the time. UberVexer fucked around with this message at 17:02 on Feb 18, 2014 |
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Feb 18, 2014 16:54
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I made a little numeric keypad to arduino to relay circuit for my dad's garage so he can enter a code to get into the garage (the old pushbutton entry from the 60s corroded and was not the safest). I just moved the prototyped circuit to one of these proto boards (similar to, might not be the exact one) and soldered it up: http://www.amazon.com/gp/product/B0040Z3012/ Everything seems to be working and I'm going to cut some holes for the power jack, relay, keypad plug and reset switch in a project box and get it all mounted in there soon. Should I coat the copper traces on the board with clear nail polish or something to protect them? I expect it to be inside a project box on a rafter in the garage for years. I'm going to do my best to seal around the openings with some sealant or maybe hot glue so I doubt much will get in, but you never know about humidity and the like. The project box is: http://www.amazon.com/gp/product/B00D5T8CQW/
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Feb 19, 2014 09:46
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Check out the closed captioning on this video; this woman's accent is so intense that youtube thinks she's saying some pretty messed up stuff about BACnet. https://www.youtube.com/watch?v=H3BNFqDYYcM
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Feb 19, 2014 16:02
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Rexxed posted:I made a little numeric keypad to arduino to relay circuit for my dad's garage so he can enter a code to get into the garage (the old pushbutton entry from the 60s corroded and was not the safest). I just moved the prototyped circuit to one of these proto boards (similar to, might not be the exact one) and soldered it up: Clean the traces with alcohol to get all flux and human-grease off, those cause corrosion. Then, yeah, I guess nail polish would work. You can get a spray-on varnish if you're really worried about humidity, which should be pretty much the same thing.
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Feb 19, 2014 16:55
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Rexxed posted:I made a little numeric keypad to arduino to relay circuit for my dad's garage so he can enter a code to get into the garage (the old pushbutton entry from the 60s corroded and was not the safest). I just moved the prototyped circuit to one of these proto boards (similar to, might not be the exact one) and soldered it up: Depending on how big the board is it might be worth it to get a PCB made up. I always find it fun to have a board manufactured and assemble it myself. It's how I decide a project is "complete" OSHPark or SeeedStudio boards come with a soldermask and a silkscreen to protect the traces and make the boards easier to solder. ante posted:You can get a spray-on varnish if you're really worried about humidity, which should be pretty much the same thing. I've seen people use something like krylon spray on clear coat before, I'm no chemist by any standards, and I'm not sure if it actually worked.
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Feb 19, 2014 17:00
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Hi folks. I can't wrap my head around this elementary circuit and I thought maybe you could help.  I'm getting two different answers depending on which current direction I select. When I select counterclockwise and apply KVL I get 5Ix-50Ix-5=0, so Ix = -0.011A indicating the correct direction is clockwise. But if I select a clockwise current direction from the start, the only way I see it is 5-50Ix-5ix=0, which gives a different answer of 0.091 A. What am I failing to understand here?
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Feb 19, 2014 19:14
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Something is missing from the drawing. The direction of Ix through R needs to be specified, otherwise the function of the current-dependent voltage source is ambiguous.
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Feb 19, 2014 20:02
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Alright that's good then. The book says "Here, the current direction is arbitrarily selected to be counterclockwise..." then in solving the circuit shows that it actually goes clockwise. I guess I'm still confused since changing the direction of the current before solving still yields a different value entirely. At least now I know it's just ambiguous that the "arbitrarily selected" current direction is part of the premise, not the solution. Thanks very much.
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Feb 19, 2014 20:35
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5 - 50Ix - 5Ix = 0 Ix = 5/55 OR 5Ix + 50Ix - 5 = 0 Ix = 5/55
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Feb 20, 2014 00:03
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Seems like that second equation would indicate a voltage gain over the resistor. Oh well, the way I was thinking about it isn't a real problem, I guess. Thanks for the help.
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Feb 20, 2014 02:18
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I want to set up simple machine with an input knob and a bipolar stepper motor so that when the knob is turned the stepper turns the same amount. Using an identical stepper as input seems like a convenient way to handle it. Just playing around I wired two motors directly to each other with no power source, and spinning one shaft will generate enough power turn the other one, which is kinda fun, but it only picks up fairly fast movements. Could I just slap a stereo audio amp in between the two motors(one audio channel per coil) and crank the gain to make it pick up more subtle movements? What would be the simplest solution for something like this? The motion doesn't have to be perfect, a missed step here or there would probably be fine, as long as it feels generally responsive and consistent.
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Feb 20, 2014 09:33
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Assuming your steppers are identical, with a nice simple scheme like that your resolution will be limited by the number of poles of the permanent magnet in the stepper's guts, I think. An [op]amp wouldn't hurt though.
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Feb 20, 2014 19:23
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The robust way would be to use a rotary encoder and a cheap microcontroller, but your way is more elegant.
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Feb 20, 2014 19:52
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The Royal Scrub posted:Seems like that second equation would indicate a voltage gain over the resistor. Whether it's a gain or a drop is just dependent on current direction. It may be a negative gain (a drop) or a negative drop (a gain) depending on the circumstances. It's all the same absolute value, whether you call it a gain or a drop and what the sign is depends on the direction you arbitrarily draw your current arrow.
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Feb 20, 2014 23:30
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Sagebrush posted:The robust way would be to use a rotary encoder and a cheap microcontroller, but your way is more elegant. Finally, the time I wasted reading that WW2 submarine manual pays off! https://en.wikipedia.org/wiki/Synchro
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Feb 21, 2014 03:43
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I have been playing with 5050 led strips. I am intrigued by the idea of combining warm, regular and cool white led strips that seamlessly change the color temperature and intesity during the day. I wake up to light, this would provide a nice alarm clock as well as give me some kind of guess to what the time is. Here is my concept: http://imgur.com/e546s24 In principle, one RGB controller would be enough for three white strips, but the cheap ones I have provide 3x4 A output max. Also, this provides the option of swapping out the white strips for RGB. The most fancy way would probably be to make a custom controller with arduino / raspberry pi that has 3 PWM outputs, but I am looking for the easiest way to accomplish this. Any thoughts?
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Feb 22, 2014 12:22
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What's the cheapest way to speak to a microcontroller wirelessly from a computer, assuming a relatively short range (10-20 meters at most) and an environment where you might have up to six computers and microcontrollers operating simultaneously and need to avoid interference between them? The little 315/433mhz RF pairs you can get all over eBay are certainly cheap and easy to implement on the microcontroller side, but you'd need a custom board to interface them with a computer, and I don't think they handle collisions and interference at all. The NRF24L01 is a lovely little thing that seems almost perfect, but it is infuriatingly hard to find a cheap USB bridge for one, so you'd probably need to roll your own and write drivers and the like. Wifi is probably out for cost reasons, but if anyone can point to a very inexpensive (<$10) wifi module that could be driven by something on the level of an Arduino that would be great. XBee stuff is another good option that's way too expensive for my project. Bluetooth seems to be the best way at the moment, with serial bridge modules available for about $6 and a USB bluetooth module being really cheap too. I would believe it's a pretty robust protocol re. collisions but I'm concerned about the range. Does anyone know of anything else that I'm missing and/or have any other recommendations?
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Feb 23, 2014 22:26
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Sagebrush posted:Bluetooth seems to be the best way at the moment, with serial bridge modules available for about $6 and a USB bluetooth module being really cheap too. I would believe it's a pretty robust protocol re. collisions but I'm concerned about the range. I used bluetooth on my old RepRap machines, and they were good for about 40 feet indoors.
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Feb 23, 2014 22:29
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Sagebrush posted:The little 315/433mhz RF pairs you can get all over eBay are certainly cheap and easy to implement on the microcontroller side, but you'd need a custom board to interface them with a computer, and I don't think they handle collisions and interference at all. Arduinos come preinstalled with everything you need to get it talking to a computer via USB, so it isn't actually that hard to get them talking.
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Feb 23, 2014 22:42
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No, I don't want a whole Arduino on each end. Ideally I want the minimum possible hardware on the computer side and an open-ended pipe on the other that I could hook to an ATTiny or MSP430 or whatever else can bit-bang a UART or I2C or whatever. The NRF24 appears to be the perfect device except for it not having a simple USB to serial bridge dongle or something, at least that I can find anywhere. Wifi is great because it needs zero extra hardware on any computer made in the last ten years, but it's harder to handle on the microcontroller end.
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Feb 23, 2014 22:50
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Bluetooth would be my choice, the receivers are just serial bridges and bluetooth already gives you adaptive frequency hopping to avoid interference. As a bonus most laptops and tablets already support serial bluetooth ports. I'd still want to have some basic checksumming on the data, and maybe retransfer if you need it but even an MSP430 should be able to do a CRC in real time. For range, if you could put the bluetooth modules in an elevated position with line of sight that should work very well, extending the USB cable is better than extending the antenna IMO.
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Feb 23, 2014 23:01
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Sagebrush posted:The NRF24L01 is a lovely little thing that seems almost perfect, but it is infuriatingly hard to find a cheap USB bridge for one, so you'd probably need to roll your own and write drivers and the like. You'd just configure libUSB to give you a generic serial port and you're good to go. Any way you slice it, you're still going to have to roll your own protocol between the host machine and the base station node regardless of which RF technology you use.
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Feb 24, 2014 15:10
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How are the FTDI cables for SPI? I've had great success using them with a micro on UART. $10 ought to be cheaper than an arduino, although certainly more expensive than rolling your own.
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Feb 24, 2014 16:34
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When I was in college, my friends and I hooked an old car battery to some thick threaded rod, and banged them together to make sparks, cleave through tin foil, etc. In retrospect, this was highly dangerous, but I'm wondering if it's possible to make it safe. Lead acid batteries have current specifications over various timeframes (e.g. 720 A for 5 seconds, 360 A for 30 seconds, and 50 A long-term). A naive solution would be to just cap current at 50 A, but what kind of circuit could do that safely? Even better would be to allow the short-term current bursts (e.g. 360 A for 30 seconds), perhaps governed by a microcontroller that's doing a moving window average or something. I have even less of an idea how to do that...
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Feb 24, 2014 20:53
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Stabby McDamage posted:When I was in college, my friends and I hooked an old car battery to some thick threaded rod, and banged them together to make sparks, cleave through tin foil, etc. Define "safe", "safe" as in the battery won't explode or "safe" as in if you get shocked you won't die? If you just want big cool sparks with a reasonable "shocked" safety margin I'd look into a Van de Graaf generator. EDIT: To be fair a 12 volt battery probably won't shock you anyway now that I think about it, but you'll still probably have a more fun time with a Van de Graaf
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Feb 24, 2014 23:45
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Stabby McDamage posted:When I was in college, my friends and I hooked an old car battery to some thick threaded rod, and banged them together to make sparks, cleave through tin foil, etc. Eh. Yes, if you weren't taking proper safety precautions, but it's inherently no more dangerous than stick welding. In fact, a pair of car batteries in series, sourcing a hundred or so amps at 25v, will do a pretty fine job as a welding power supply with simple rods like 6018 if you need to repair your 4x4's frame in the middle of the desert or something.
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Feb 25, 2014 02:24
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Sagebrush posted:Eh. Yes, if you weren't taking proper safety precautions, but it's inherently no more dangerous than stick welding. In fact, a pair of car batteries in series, sourcing a hundred or so amps at 25v, will do a pretty fine job as a welding power supply with simple rods like 6018 if you need to repair your 4x4's frame in the middle of the desert or something. I was looking to do some small time welding (like a nut to a threaded rod, maybe twice) I think I'll give this a go. Is it appropriate to just use jumper clamps for holding the stick and clamping the piece?
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Feb 25, 2014 04:07
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