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On a PC the port should be limited but probably won't be. I think most USB ports just connect straight to the PSU 5V rail, on my board (nForce chipset) there's a jumper to select 5V or 5V standby (to allow the keyboard to wake the computer). Not recommended but I do power two external fans from the motherboard port and a PDA and some fairly beefy (200mA) LED lamps from a powered hub, no real problems with any of them. The hub stops working as a hub if the external power is disconnected though.
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Feb 10, 2011 15:41
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I should have been more clear, I was using the USB on an external powered hub, and now it resets occasionally disconnecting my mouse and keyboard. It was a cheap chinese-made hub and drawing a shitton of current probably stressed one of the parts. I haven't popped the case for a visual inspection yet, but I probably will eventually. And I meant "don't short out your power rails" not "don't use USB for power". I mean, there is 5v, regulated, ready to go. Why wouldn't you? 
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Feb 10, 2011 16:27
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I know not everyone follows the rules ( ), but a resettable fuse is required by the USB spec.
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Feb 10, 2011 17:02
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Delta-Wye posted:And I meant "don't short out your power rails" not "don't use USB for power". getting an FTDI usb to TTL cable has made micocontroller developing about 600 times nicer, since USB power is enough for about 80% of things I do. Basically what I'm saying is USB power rules, and the cable has a resettable fuse in it.
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Feb 11, 2011 00:25
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ANIME AKBAR posted:Yes. I'm actually jealous. I've tried to convince my superiors of the value of such a project but it keeps falling on deaf ears. You don't have to completely reengineer the scanner. Do your ADC and Tx at the coil, then do your Rx and DAC inside a module that plugs into the doghouse. There's at least one company out there that manufacturs such a module, and the big vendors are going to be incorporating this functionality into their future hardware.
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Feb 11, 2011 01:33
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I'm fairly new to this and something is still bugging me about current and diagrams. So, in actual current, the electrons flow from negative to positive terminals, because electrons have a negative charge. In traditional current, as in circuit diagrams, the flow is depicted from positive to negative terminals. But, it doesn't really matter as long as polarized components are hooked up positive to positive and negative to negative? Do the two current paradigms present any issues when following a certain diagram or using certain components?
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Feb 11, 2011 15:16
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standardtoaster posted:I'm fairly new to this and something is still bugging me about current and diagrams. For the most part, ignore the "electrons flow from negative terminal to positive terminal  " business when you're first starting out. It's needlessly complicating and doesn't matter until you start getting into the physical properties of materials (doping levels of silicon and stuff like that). Ideally by the time you get to talking about nitty gritty doping levels and stuff, this will be so old-hat to you it won't be an issue anymore.
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Feb 11, 2011 16:35
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standardtoaster posted:I'm fairly new to this and something is still bugging me about current and diagrams. You are correct that the traditional sign convention shows current flowing from positive to negative voltage while the physical electrons are actually flowing from negative to positive. It's a historical fluke, people began playing with electricity and had a notion that something was flowing long before they understood what electrons are. They just picked a sign convention at random, and from the viewpoint of a physical electron they picked the wrong one. The good news is that for normal circuit analysis the sign convention doesn't matter. If you pick one convention and stick with it consistently you will get the same answers as if you had picked the other convention. Only your interpretation of the current will change - you would describe a current as "1mA flowing from A to B" or as "-1mA flowing from B to A" depending on which sign convention you picked. Mathematically it's the same current either way. 99% of the world uses the postive-to-negative current flow definition, so just go along with it to avoid confusing yourself and others. The other 1% are semiconductor engineers who really need to know where the physical electrons are going from and to, but if you don't work at Intel it's not a problem. PDP-1 fucked around with this message at 16:57 on Feb 11, 2011 |
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Feb 11, 2011 16:53
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Thanks, that confused the poo poo out of me in that stupid Electronics for Dummies book. I ditched that and bought a Basic Electronics text book at a used book store for $5. Much better.
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Feb 11, 2011 17:09
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Cyril Sneer posted:I'm actually jealous. I've tried to convince my superiors of the value of such a project but it keeps falling on deaf ears. quote:There's at least one company out there that manufacturs such a module, and the big vendors are going to be incorporating this functionality into their future hardware.
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Feb 12, 2011 04:00
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So I need to run as many Infrared LEDs as possible off of a usb to serial port adapter. Can anyone recommend a simple circuit and some LEDs?
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Feb 12, 2011 08:38
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standardtoaster posted:Thanks, that confused the poo poo out of me in that stupid Electronics for Dummies book. Engineering textbooks go through editions so quickly that this is an excellent way to learn. Old editions are still plenty relevant and everything from fancy math to extremely convoluted electrical engineering nonsense can be had for less than  at half price books.
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Feb 12, 2011 16:07
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Tres Burritos posted:So I need to run as many Infrared LEDs as possible off of a usb to serial port adapter. Can anyone recommend a simple circuit and some LEDs? Which USB to serial port adapter are you using? Some adapters do an internal DC/DC voltage conversion that transforms the +5V of the USB line into the +/-12V signals normally used in RS-232. The USB port may be able to supply several hundred milliamps at 5V but after the voltage conversion you might only have 1-2 milliamps available on the serial port pins. For applications where you only want to connect two things for data communication the low current is fine since you would only be driving a few input pins on the RS-232 listening side, but for what you want to do 1-2 mA is not really enough to light up a bunch of LEDs. What are you plugging the cable into? It might have its own power supply that you could run the LEDs off of or you could run a second, unconverted USB line alongside the communication line to act as a power source.
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Feb 12, 2011 17:45
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PDP-1 posted:Which USB to serial port adapter are you using? Some adapters do an internal DC/DC voltage conversion that transforms the +5V of the USB line into the +/-12V signals normally used in RS-232. The USB port may be able to supply several hundred milliamps at 5V but after the voltage conversion you might only have 1-2 milliamps available on the serial port pins. For applications where you only want to connect two things for data communication the low current is fine since you would only be driving a few input pins on the RS-232 listening side, but for what you want to do 1-2 mA is not really enough to light up a bunch of LEDs. Perhaps if I explained what I'm doing it would clear some things up. I'm trying to control a mini helicopter from my computer. As it turns out someone has already gone through the trouble to do this and documented their struggle here. I'm already pulling axis information from my joystick, so my next step is to start coding the transmission part. Problem is, I don't have anything to transmit with. So I'm just trying to make a set of a couple (3?) leds that I can control from my computer. The hardware setup that the other guy used is right here. I figure, he can run 3 LED's off of usb, it should be within the realm of possibility that I can do it too. I figured since I had a serial port adapter already sitting around (a "PL-2303") I'd just use one of those instead, if I could manage to set it up. edit: Datasheet for the 2303 if that helps? Tres Burritos fucked around with this message at 20:27 on Feb 12, 2011 |
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Feb 12, 2011 20:23
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Ah, OK that does help. I thought you were talking about the cables that plug into a USB port and provide an RS-232 connection on the other end. Those have charge pumps inside to get the +/-12V RS-232 signals and the charge pumps kill your available output current. It looks like the guy you linked to is using a USB-Serial bridge chip without any charge pumps so the whole system runs off the 5V USB power supply. That means you can power the LEDs directly off of the USB line which is good. Skimming through the info he posted, it looks like he's doing something like this:  The USB connector is on the left and sends data to the bridge chip. The data gets converted to serial and sent out the transmit pin Tx. When Tx goes high it turns on the transistor and lets current flow through the LED. When Tx is low the transistor shuts off and the LED shuts off too. There should be some filter caps on the 5V line since the LED will draw a lot of current when switched on, and make sure that your Tx pin can source/sink enough current to run the transistor. Does that make sense based on your understanding of the helicopter control? Is there any data coming back from the helicopter?
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Feb 12, 2011 22:31
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Yeah. Makes perfect sense. Nothing gets received from the helicopter. The receiver that he built was so that he could decode the info coming from the transmitter. So I just need to find a female serial connector, some LEDs, a resistor and a transistor? Can you recommend any values for them?
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Feb 12, 2011 23:48
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The best bet would be to ask the guy if he'd share a parts list or schematic with you. He seemed to be pretty open with his info on that forum. If that doesn't work you could just get an infrared LED from Radio Shack. Assuming that it had a 1.5V forward voltage drop and drew 100mA, then for a 5V supply with 0.7V across the transistor when its on you'd need R2 = (5V - 1.5V - 0.7V) / 100mA = 28 Ohms The pdf spec sheet for that chip you posted was pretty vague, they just list the Tx pin as some kind of 'TTL compatible' output so you don't want to draw more than 0.4 mA or so when it's on. That suggests that you'd need a transistor with a beta of (100mA / 0.4mA) = 250 and R1 = 10.7k Ohms. You might also think about using a Darlington pair driver in place of the transistor so you could just connect the TTL signal directly into the input and drive multiple LEDs at once. PDP-1 fucked around with this message at 01:27 on Feb 13, 2011 |
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Feb 13, 2011 01:15
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PDP-1 posted:You might also think about using a Darlington pair driver in place of the transistor so you could just connect the TTL signal directly into the input and drive multiple LEDs at once. Double edit: These digikey part #s? Darlington LED Resistor Tres Burritos fucked around with this message at 04:01 on Feb 13, 2011 |
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Feb 13, 2011 01:30
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Anyone have a USB oscilloscope that they like? I'm looking for an inexpensive scope for small projects, and hoping to find a solid reliable one with decent software.
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Feb 13, 2011 04:35
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I'm currently sort of rebuilding the northpaw concept. ( http://sensebridge.net/projects/northpaw/ ) since I dont like their implementation aesthetics, but I'm fascinated with the idea. So here is my parts list so far: http://www.sparkfun.com/products/10181 http://www.sparkfun.com/products/7915 http://www.sparkfun.com/products/8449 x8 plus this for the seeeduino http://shop.moderndevice.com/products/usb-bub Now I've never programmed any arduino stuff before, so I'm pretty excited and I'll let you guys know how it goes. However, in terms of powering the thing, what I'd like to do is build my own lipo battery pack using a few of these cells http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7568 and some sort of protection circuit I assume. I'm thinking those cells because they're the right size to place around the anklet without interfering. I figure that my power usage will be around 0.2w (I'm basing this on the seeeduino and motor running constantly, which wont be the case, but design for the limits) so I'd like about 3-4w/hrs of battery, assuming 12-18 hours of use at a time, ie a full day. Has anyone attempted to build their own lipo battery pack before?
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Feb 13, 2011 12:58
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devians posted:Has anyone attempted to build their own lipo battery pack before? Yes, and the experience taught me all the fun things lipo batteries do when you don't treat them nicely; inflate like balloons, get hilariously hot, rolling black smoke, etc. If you're putting them in parallel you shouldn't have to worry much about cell balancing as they should self-balance. In fact, if you're wiring is correct I think you can treat them as a single large cell. Just keep in mind you need a dedicated lipo charger (or something like http://www.sparkfun.com/products/674) and you don't want to overdischarge them. EDIT: Be careful, the jokes about these batteries burning your house down aren't so funny if it actually happens to you. Be sure to double-check your wiring, and be prepared in case things go south. Those little batteries can source 5A a piece without problem, they can dump a hell of a lot of current very quickly through a dead short. Delta-Wye fucked around with this message at 19:38 on Feb 13, 2011 |
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Feb 13, 2011 19:35
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I'm looking for a cheaper alternative to this pressure sensor that has the same basic characteristics, i.e. just a couple pins, probably not requiring a huge amount of circuitry to drive it, and is good for use as an electronic weight scale. I don't need the whole flexible business, I really just need the sensor at the end with a couple pins. I'd look it up on digikey but I don't really even know where to start as far as picking one product over another. Oh, and the reason I don't want to get the one linked above is because I need 8 of them and that would cost me $160. Also really want to go with KISS on this one. (Since I know Delta Wye's about to say something crazy or whatever.) Bad Munki fucked around with this message at 06:19 on Feb 14, 2011 |
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Feb 14, 2011 06:17
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Bad Munki posted:I'm looking for a cheaper alternative to this pressure sensor that has the same basic characteristics, i.e. just a couple pins, probably not requiring a huge amount of circuitry to drive it, and is good for use as an electronic weight scale. I don't need the whole flexible business, I really just need the sensor at the end with a couple pins. I'd look it up on digikey but I don't really even know where to start as far as picking one product over another. I'm a fan of the idea of building a capacitive pressure sensor - something like this: http://blog.makezine.com/archive/2009/11/diy-capacitive-pressure-sensor-tile.html Then it's just a matter of measuring the capacitance (or use it in an RC oscillator or 555 circuit and measure frequency) to get the weight. Plus, you're not stuck measuring pressure on a quarter inch circle. And tin foil is a hell of a lot cheaper than $160! EDIT: Ouch. It's the electronics MEGATHREAD. Go complicated or go home!
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Feb 14, 2011 06:20
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Delta-Wye posted:Yes, and the experience taught me all the fun things lipo batteries do when you don't treat them nicely; inflate like balloons, get hilariously hot, rolling black smoke, etc. If you're putting them in parallel you shouldn't have to worry much about cell balancing as they should self-balance. In fact, if you're wiring is correct I think you can treat them as a single large cell. Just keep in mind you need a dedicated lipo charger (or something like http://www.sparkfun.com/products/674) and you don't want to overdischarge them. Ah yes, well aware of the 'burn down your house' factor. Mate of mine had his quadcopter fall out of the sky at 4 or so stories, the lipo hit the concrete pretty hard. Fun to watch, but he wasn't impressed. So in terms of wiring them together, i think i only need 3.3v, so in parallel should be fine. I'm going to pick up an assortment from hobby king to play with. Is it possible to mix and match capacities? ie 240 and 400 ma or will that cause fire? Also, should i be looking into something like this http://www.batteryjunction.com/prcimopcbfor.html ? Or at least something to prevent damaging discharge.
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Feb 14, 2011 09:14
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I don't wanna use lipos anymore.  http://www.youtube.com/watch?v=z3o_2mwRPdw
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Feb 14, 2011 21:23
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I've been looking at the LPC1114 version of the LPCXpresso boards: http://ics.nxp.com/support/lpcxpresso/pdf/lpc1114.schematic.pdf Some of the components, for example C19 & L1, have a value of "UL". I haven't seen this before. Does it mean unlimited? I don't feel like that makes very much sense. Maybe "Unused Location" or similar? Screencap showing on of the UL components: 
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Feb 15, 2011 19:02
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Bad Munki posted:I'm looking for a cheaper alternative to this pressure sensor that has the same basic characteristics, i.e. just a couple pins, probably not requiring a huge amount of circuitry to drive it, and is good for use as an electronic weight scale. I don't need the whole flexible business, I really just need the sensor at the end with a couple pins. I'd look it up on digikey but I don't really even know where to start as far as picking one product over another. I built something like this for a project a couple years ago. It was really similar to this: http://www.instructables.com/id/Flexible-Fabric-Pressure-Sensor/ Much cheaper than what you were talking about, and no need to measure capacitance like in Delta-Wye's suggestion. Resistance drops to nearly zero when when you apply pressure, just use a voltage comparator to measure the difference. I still have an image of the schematic I used if you want.
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Feb 15, 2011 19:50
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taqueso posted:I've been looking at the LPC1114 version of the LPCXpresso boards: http://ics.nxp.com/support/lpcxpresso/pdf/lpc1114.schematic.pdf The bottom of the first page of the pdf you linked has the note "UL = UnLoaded = normally not mounted component", so I'd guess there are just some holes on the PCB where you can solder in the extra components if you need some extra functionality, or maybe access to some debugging/prototyping abilities.
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Feb 15, 2011 21:34
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PDP-1 posted:The bottom of the first page of the pdf you linked has the note "UL = UnLoaded = normally not mounted component", so I'd guess there are just some holes on the PCB where you can solder in the extra components if you need some extra functionality, or maybe access to some debugging/prototyping abilities. Thanks for doing my reading for me. 
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Feb 15, 2011 22:25
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Corrupt Politician posted:I built something like this for a project a couple years ago. It was really similar to this: While that's more than a little awesome, I'm guessing he needs a little more accuracy for a weight sensor. There's a handful of Interlink resistive force sensors on Digikey that are pretty affordable (<$10). "Pressure sensor" seems to generally apply to industrial process pressure sensors which need quite a bit of hardware to be adapted to the sort of application I'm guessing you're after.
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Feb 15, 2011 22:45
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I ordered one of these from sparkfun. They say it might not be accurate enough for a scale, but looking at the datasheet, the response curve looks totally workable to me. Also, I figure I can just put various known weights on it to get some reference points. Worst case scenario, it doesn't work out, and I'm out $6 but have a nifty unallocated sensor. I'm okay with that.  Interesting tidbit: that sensor and the flexiforce one both cost about $3 MORE from digikey, for the exact same product. I would have expected to pay a small premium for going through SF, but apparently it's the other way around. Although I suspect that digikey's bulk discounts are better (but haven't checked.)
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Feb 15, 2011 23:00
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Digikey is actually about $0.10 cheaper per unit on that one than Sparkfun, so you might as well order from the place with lower shipping costs. The 1/2" has a bigger spread, $0.41. I like Sparkfun but I'd be crazy to ever order anything other than kits. Digikey ships (across the state) in 2-3 days maximum and they are incredibly good about doing small hobbyist orders. On another note, does anybody know an automated method for turning a SPICE model into a mathematical model other than good old pen and paper? I've been working on trying to convert some old synthesizer stuff to time-domain math for either computer or FPGA implementation. Linear things (filters) are pretty trivial but things like saw-square converters and oscillators are a huge pain.
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Feb 15, 2011 23:51
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Oh, I guess I was just remembering from the flexiforce sensor. Oh well.
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Feb 15, 2011 23:56
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sixide posted:I like Sparkfun but I'd be crazy to ever order anything other than kits. Digikey ships (across the state) in 2-3 days maximum and they are incredibly good about doing small hobbyist orders. I've gotten stuff from Digikey next day on their standard $8 shipping. And I live in Canada. Their shipping is incredible and is part of why I love them so much.
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Feb 16, 2011 00:06
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Thief River Falls is about as close to Canada as you can get without being directly on the border.
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Feb 16, 2011 00:11
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When did Sparkfun become all slow? It's been three days and so far, according to my order history, they've managed to print off the invoice. I admit it's been a while since I ordered anything from them, but I swear they used to be a hell of a lot faster than this. 
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Feb 17, 2011 00:03
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Bad Munki posted:When did Sparkfun become all slow? It's been three days and so far, according to my order history, they've managed to print off the invoice. I had a similar experience recently. Wonder if they're still backlogged from the recent "free day."
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Feb 17, 2011 01:05
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BattleMaster posted:I've gotten stuff from Digikey next day on their standard $8 shipping. And I live in Canada. Their shipping is incredible and is part of why I love them so much. it depends on where you are, I get stuff from Mouser the next day, Digi-key usually takes 2-3.
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Feb 17, 2011 01:27
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Bad Munki posted:When did Sparkfun become all slow? They've been out of poo poo I need for like a month.
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Feb 17, 2011 02:00
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At this point, I'm sorta actually considering putting in an order with digikey for the same parts, since I imagine I could get the stuff by Friday or Saturday. With SF, I suspect I may be waiting well into next week. This does not sit well with my need for instant gratification.
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Feb 17, 2011 02:11
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