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My PoE injector is a 48V 12.5W unit, you could get a standard PoE injector and make your own step-down at the other end. Otherwise for getting a working system running I recommend just buying eBay step up/down converters. They usually work up to 15W with passive cooling and can typically do 30V. I bought a pile of them to keep around, very useful for quickly hacking together things.
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May 18, 2012 09:17
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I have a circuit with two parts. A has large changes in loads, B has a LDO. The supply to the LDO varies slightly when the load of A changes, this causes the output of the LDO to ring. So I was trying to figure out how to reduce the ringing on the LDO. I tried adding various caps and also adding an intermediate LDO. I then measured the ground clip and found that the ringing was on the ground as well. Now I'm confused. How does the oscilloscope measure a non zero voltage when measuring it's ground clip? So the basis setup is DS1052E, two probes with ground clips connected to the same circuit ground at the same point. One probe measure the output of the LDO, and is triggered when it rings. The other probe is measuring the ground clips and also has ringing.
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May 18, 2012 13:36
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FSMC posted:I have a circuit with two parts. A has large changes in loads, B has a LDO. The supply to the LDO varies slightly when the load of A changes, this causes the output of the LDO to ring. So I was trying to figure out how to reduce the ringing on the LDO. I tried adding various caps and also adding an intermediate LDO. I then measured the ground clip and found that the ringing was on the ground as well. Now I'm confused. How does the oscilloscope measure a non zero voltage when measuring it's ground clip? Seeing this kind of thing isn't surprising, especially when the transient load has fast rise/fall times. What you're seeing is either common mode signal coupling through the scope's earth connection, or EMI coupling into the loop formed by the probe's ground clip. An easy way to test if it's EMI is to just clip the ground lead of the probe to its own tip (but not to the circuit ground, the circuit should be isolated), then bring that loop close to the circuit. If you see the ringing, then it's EMI (partially, at least). Try shrinking the size of that ground probe loop, with something like this:  It that doesn't make the ringing go away when probing your own ground, then you may need a true differential probe.
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May 18, 2012 14:25
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FSMC posted:I have a circuit with two parts. A has large changes in loads, B has a LDO. The supply to the LDO varies slightly when the load of A changes, this causes the output of the LDO to ring. So I was trying to figure out how to reduce the ringing on the LDO. I tried adding various caps and also adding an intermediate LDO. I then measured the ground clip and found that the ringing was on the ground as well. Now I'm confused. How does the oscilloscope measure a non zero voltage when measuring it's ground clip? It might be worth including a schematic or block diagram. Where are you measuring the power rail? Directly across the power/ground pins of the load? Or directly at the output of the LDO? Or do you have the ground at the LDO and the power at the load? Ground is not always constant, especially if you have inductance in the ground connection, like a wire or a small trace. When you added capacitance, were you adding that at the load, or at the LDO output? Of course, this could be caused by a few other things as well. Depending on your circuit, your LDO could be slightly unstable or have low phase margin. This might be true if you didn't follow the recommended output capacitance of the LDO (ESR and total value) or placed the output capacitors too far away. It could also be caused by the scope itself - some scopes will include a DSP filter to compensate for losses in the signal chain. This filter can ring when you get a fast transient, even if there is no problem in the actual circuit.
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May 18, 2012 14:44
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ANIME AKBAR posted:Seeing this kind of thing isn't surprising, especially when the transient load has fast rise/fall times. What you're seeing is either common mode signal coupling through the scope's earth connection, or EMI coupling into the loop formed by the probe's ground clip.
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May 18, 2012 15:40
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Let's make out.
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May 18, 2012 19:11
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Let's say I have four current drivers and four rows of LEDs. The positive wire from each current driver is connected to the positive terminal of the first LED of each row. On the negative side of the last LED in each row, can the wire splice back into a single conductor and then divide again back into each current driver or will this not work correctly? Here's a diagram if I'm wording this in a confusing way:code:
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May 18, 2012 20:16
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The side of the current sources that you can connector together depends on whether the sources are sourcing or sinking current. Which might also vary with the type of source--buck regulator or boost regulator (the latter is less common for powering LED strings, usually just for powering one or two LEDs on mobile devices). On the other hand, there might be some LED drivers that require each string be completely isolated, but that'd have to be some weird topology, I guess... EDIT: Thinking about it for another minute, I'm still pretty sure that drivers using some sort of buck topology could go either way, in terms of sourcing or sinking current, at least if they were meant for low voltage + low current (otherwise you enter the realm of having to worry about different requirements for high or low side switching). Slanderer fucked around with this message at 20:33 on May 18, 2012 |
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May 18, 2012 20:28
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FSMC posted:Thanks, I used that attachment you suggested and it worked perfectly and got rid of the ringing. I'm a bit surprised because I didn't realise that EMI would have such a large effect, on the LDO output, Average of 3.3V but the ringing went from 2.0V to 4.8V which is quite a lot. It looks like an inductor in section A is causing the EMI.
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May 18, 2012 23:53
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ANIME AKBAR posted:So you mean that when using the ground pin adapter, you don't see ringing on ground, but you do on the LDO output? That's surprising, since in general LDOs have excellent transient response. I'd bet you're either still seeing EMI, or the LDO is bad or isn't being used correctly (some require certain amounts of capacitance with some amount of ESR to work properly). Sorry I wasn't clear. The ringing on the LDO pretty much disappeared when I used the ground pin adapter to measure the output. I was just surprised by the magnitude of the effect EMI had on the measurements when using the ground clip.
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May 19, 2012 00:48
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Hidden Under a Hat posted:I have some more issues with solid state relays. When you attempt to turn off the solenoid its self inductance is causing a large voltage spike to appear at the contacts of your solid-state relay. This spike is causing either a false trigger of the gate-drive or perhaps even a breakdown of the switching FET in the SSR. Either event can cause the FET to continue to conduct and leave the solenoid coil energized. The simplest way to inhibit this voltage spike is to use a diode wired in parallel with the solenoid coil. The anode needs to be on the low side and the cathode on the high. (If the polarity is reversed from this the diode will essentially short out your load.) This "catch diode" will limit the voltage at the SSR terminal to a forward-voltage drop higher than VCC (if switching on the low side) or a forward drop more negative than ground (if switching on the high side). The datasheet for the SSR illustrates this on page 3. One downfall of the above clamp circuit is that it can inhibit the actual mechanical action of the solenoid. The reverse voltage that appears at the solenoid coil is a manifestation of the magnetic force which the coil exerts on the valve. If you reduce this voltage then there's less force applied which yields a longer switching time - and worst case the force might be so low that the solenoid "sticks." A better approach is to allow the coil to produce some "safe" amount of reverse voltage but not enough to cause a switching problem with the SSR. This can be accomplished by adding a zener diode in series with the clamp diode. (Some experimentation will likely be required to determine the proper value.) The above are both examples of a diode snubber. More generally a snubber refers to any circuit used to inhibit voltage transients either by reducing amplitude (the clamping diodes above) or dv/dt. Reducing dv/dt is accomplished with a series RC network in parallel with the switching component. Generally these are used only when you need to reduce the high-frequency content in switching waveforms in order to meet EMC requirements, or if a diode snubber isn't suitable such as with a triac. Boy With Stick fucked around with this message at 12:14 on May 19, 2012 |
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May 19, 2012 04:12
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Can anyone recommend a good beginners book on electronics? I've been getting those little Velleman kits from Radio Shack and they're good for soldering practice, but I want to know how/why these parts make an LED blink.
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May 19, 2012 18:00
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Fooley posted:Can anyone recommend a good beginners book on electronics? I've been getting those little Velleman kits from Radio Shack and they're good for soldering practice, but I want to know how/why these parts make an LED blink. I guess I'll be the first to recommend the Art of Electronics by Horowitz and Hill. It's the best comprehensive guide to a broad range of electronics topics that I've found, and it's pretty accessible to beginners.
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May 19, 2012 19:13
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The art of electronics is extremely dated in a lot of places--namely, the digital and microprocessor stuff. The lists and tables of transistors and op amps are a funny look into the world before the internet, when you had to look up (really short) datasheets in big books...a time which scares me, since I cant imagine working without parametric search tables, free samples sent via UPS, $30 dev boards, and above all, digikey. That said, I hope that the 3rd edition still has small, updated tables (maybe as a supplement though). The general op amps I use always end up being more expensive than necessary, since picking new ones that I know will work is annoying.
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May 19, 2012 19:31
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I'm going to be moving to a new desk in my company's office that is in something of a blind corner. I'd like my teams to be able to see if I'm at my desk without having to walk a maze so I'm thinking about a way of broadcasting my presence if I'm in the area. My first idea was having a light perched on the top of my cube. The light would be connected to a Bluetooth module paired to my iPhone so that if I come within range of it, light goes on. It's the same idea as BlueProximity only with discrete components instead of a PC doing the work. My basic problem is that I've never worked with any sort of component more complicated than a Nokia LCD and I don't know if what I'm thinking about is possible for an amateur. I'm fairly comfortable with the MSP430 value line (Launchpad) microcontrollers - that particular uC might not have the stones to connect to a Bluetooth device but I could probably source one that does with a little pointing in the right direction. I have one fundamental question before I begin asking more: Is this even going to be possible, specifically with the iPhone? I was doing some initial reading on Sparkfun and in the comments on this module and apparently there's some authentication chip that Apple requires to pair with an iOS device - except possibly for HID devices? Could I get a module configured for HID and rig that somehow?
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May 20, 2012 04:12
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I've got a children's toy that I need to make louder (it's barely audible, a frequent complaint on this particular toy). Would adding a single amplifier be as easy as connecting power to the existing power switch, ground to battery ground, then splicing the amp in between the speaker and the main board? It seems too simple to me. It runs off of 3 AA batteries. Also, any suggestions on adding a charging circuit to some plug in toys? The #1 toy I have in mind is a keyboard (Vtech Kidijamz Studio, if anyone cares) that runs off of 4 AA batteries or a 9v plug. Seems like it would be simple enough, so I know it can't be that simple. Would I need to have the circuit disconnect the batteries from the rest of the circuit before charging, or can the charge the batteries without worrying about that? On a completely related note, whats the general opinion on inductive charging mats and the like? I have a few remote controls that seem like it would be great to just put them on the table and they charge. Oh, and why not just use rechargeable batteries that you replace? It's more of a case that I can't find a decent charger that lets me recharge a dozen or so batteries and keep them charged (I have 2 chargers, both handle 4 batteries each, and one of them stops charging when the batteries are charged (no trickle charge), and then starts draining the batteries for some really stupid reason. If I throw them in for a 2 hour charge, I can come back in 4 hours to dead batteries).
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May 20, 2012 22:09
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csammis posted:I'm going to be moving to a new desk in my company's office that is in something of a blind corner. I'd like my teams to be able to see if I'm at my desk without having to walk a maze so I'm thinking about a way of broadcasting my presence if I'm in the area. My first idea was having a light perched on the top of my cube. The light would be connected to a Bluetooth module paired to my iPhone so that if I come within range of it, light goes on. It's the same idea as BlueProximity only with discrete components instead of a PC doing the work. I thought about this briefly today, but maybe you could use a bluetooth module that's configured in master mode, and get it to list bluetooth devices, and look for your phone? I'm really not too sure, though, as I've never done that, and it's only briefly mentioned in the manual for one of the bluetooth modems I've used.
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May 20, 2012 22:50
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Question about ground. Is ground ground the world around? I'm still playing with this power over ethernet thing, and I've been curious a few times over different projects... Let's say I have a battery on end (A), then I send power down this long ethernet cord to a regulator, and on that far end I have a serial device, also going through that ethernet cord is the serial connection(tx and rx). Now, right now I don't bother grounding the far end of the serial connection, I just connect the ground on the battery's end to the computer's serial ground pin, and it works. I'm curious if that's really ok, or I'm just getting away with it in this circumstance. Same thing on something like a voltage regulator. Is it ok to connect whatever the regulator is powering to the battery's ground, or should it be connected to the ground pin on the regulator? That wouldn't seem to matter to me, since the regulator's ground pin is already connected to ground, but I was curious none the less.
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May 21, 2012 23:23
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Ethernet cable is shielded (Edit: depending on which kind you have). Your ground should be connected to the shield on both ends, and your components should be connected to that ground which connects to the ground of your source of power. This will keep both sides at the same ground. Ground is what tells your circuit what 0V is. If you didn't have that, then your positive voltage would not have the same meaning. What is 5V? It's 5 more volts than your ground. Without ground, that 5V is no longer 5V because it doesn't have anything to reference. As for your voltage regulator, the ground pin must go to ground not only for reference but as a temperature sink. Krenzo fucked around with this message at 07:31 on May 22, 2012 |
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May 22, 2012 00:04
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The shield should absoutely not be earth grounded at both ends. If both sides are at different galvanic potential you will cause a large current flow through the cable, which can transfer dozens of amps and potentially start a fire. And, not all ethernet is shielded. Only shielded ethernet is shielded.
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May 22, 2012 00:38
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Krenzo posted:Ethernet cable is shielded.  More information than you want to know (but less than you need to know!) about transmission lines: http://www.vagrearg.org/?p=transline
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May 22, 2012 00:54
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Delta-Wye posted:UTP - Unshielded Twisted Pair Oh, I've been using CAT-7 cable which is shielded. So yeah, your cable might be unshielded in which case, disregard what I said. Krenzo fucked around with this message at 07:46 on May 22, 2012 |
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May 22, 2012 07:07
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Krenzo posted:Oh, I've been using CAT-7 cable which is shielded. So yeah, your cable might be unshielded in which case, disregard what I said. However, if you use a shielded cable, then you won't have to worry about wasting any of your conductors on ground. You shouldn't have to "waste" any conductors on either power or ground. Just send it as common mode with power on two of the diff pairs. In ethernet they should be xfmr coupled anyway, so you can tap off the center pin. Use A/B or C/D to maintain a semblance of compliance with the 802.3 spec. And try not to push more than a few 100mA over the cable, to reduce losses and inefficiencies.
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May 22, 2012 07:57
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SnoPuppy posted:Just send it as common mode with power on two of the diff pairs. Geez, I had no idea that's how PoE worked. I was actually wasting conductors in my PoE design by sending power and ground on their own separate conductors. Though, signals in my cable are DC coupled, not AC, due to long dead time so it wouldn't help me. insta posted:The shield should absoutely not be earth grounded at both ends. If both sides are at different galvanic potential you will cause a large current flow through the cable, which can transfer dozens of amps and potentially start a fire. Can you clarify what you're saying here? I suggested he connect both sides' grounds to the shield. If he doesn't connect one side to ground which is carried through the cable, then how will his circuit receiving the power over the ethernet cable function? Krenzo fucked around with this message at 09:21 on May 22, 2012 |
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May 22, 2012 09:11
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I said earth grounded, not grounded-to-shield. Both sides will need to be grounded to the shield to complete the circuit, but only one of those sides should be tied to earth ground to mitigate EMI.
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May 22, 2012 14:57
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insta posted:I said earth grounded, not grounded-to-shield. Both sides will need to be grounded to the shield to complete the circuit, but only one of those sides should be tied to earth ground to mitigate EMI. The concept of ground is purely a notational convenience - there is nothing magical about it. Neither side needs to be at "earth ground" for EMI reasons. They could just as easily use system ground. Or +5V. Or -12V. Or any other potential that will carry the return current. So long as any current flowing through the center conductor has it's return path along the shield, the EM fields will cancel due to Gauss's Law. Concern about connecting both ends of the cable to the same "nominal" voltage (i.e. earth ground) is that the "nominal" voltage may not actually be the same at both points. Now you have a circuit connecting the cable shield between two different voltage potentials. The cable will likely be the lowest impedance between them and will conduct a large amount of current.
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May 22, 2012 17:11
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While we are on the subject of ground, I've always been confused by circuit diagrams that show a typical DC power source like a battery with positive and negative, but then also show the negative connected to a ground symbol. Other diagrams, never show the ground symbol. I've never seen this explained in any of the intro to electronics books, nor have I ever need to make some sort of connection to another ground source to get the circuits to work. Why is that ground symbol there?
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May 22, 2012 18:22
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Probably just for clarity, in a battery powered circuit there's no actual objective "ground" (there never is, voltages are relative), the net connected to a ground symbol is the system reference ground (i.e. a voltage potential that the other voltages are references to). It's helpful for larger circuits too, since you just put in more ground symbols instead of having a large wire going all over the schematic. Plus the negative side of a battery might be a negative power supply, you can call the plus side of a battery "ground" and then the negative pole would be a negative supply compared to ground. I spent a lot of time getting my head around what ground is exactly, and I doubt my explanation helped much... I think this video might help understand the practical implications though: https://www.youtube.com/watch?v=xaELqAo4kkQ Everyone should be following the EEVBlog anyway but it seems relevant.
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May 22, 2012 18:40
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longview posted:Everyone should be following the EEVBlog anyway but it seems relevant. I....I just can't listen to that man talk. Actually, watching him is annoying as hell too. I'll stick to my books, thank-you-very-much. And don't anyone get started on Jeri Ellsworth...
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May 22, 2012 19:28
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bobua posted:While we are on the subject of ground, I've always been confused by circuit diagrams that show a typical DC power source like a battery with positive and negative, but then also show the negative connected to a ground symbol. Other diagrams, never show the ground symbol. Really, the ground is just there for clarity; it serves no 'physical' purpose, but helps show the reader what the designer was trying to say. For instance, let's say you were trying to get a bipolar power supply (+- 4.5V) from a 9V battery. Something like this would give you 4.5V referenced to the batteries negative terminal:  However, if you call the 4.5V point in the middle of hte resistor divider 0V, the negative terminal becomes -4.5V and the positive terminal becomes 4.5V. Note, we haven't changed anything physically about the circuit ; it still behaves the same, we've just changed our naming. This particular circuit is common in audio applications, such as this guitar pedal:  The 'floating ground' is used bias the opamps, who draw their power from the +/- 4.5V rails.
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May 22, 2012 21:15
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I typed this up for someone in #cobol, thought you also might like to see it here. https://docs.google.com/spreadsheet/ccc?key=0AlfCS4tz1qLJdHJ3QjZwVjFVSl9lT2dsOWRzUUJsNEE This is a list of components in some EE/CompSci kits I got off of eBay. They're from the 1980s, apparently they were used at MIT. I suppose they're using FPGAs by now! At any rate this is what you need to get started with the wonderful world of digital logic. edit: Also I suppose it would be interesting if anyone had any suggestions to improve this 30-year-old kit. I'm sure we're all past low-power Schottky logic chips. Silver Alicorn fucked around with this message at 02:33 on May 24, 2012 |
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May 23, 2012 19:41
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I'm replacing some lamps in a vintage receiver (HK 430 if you're curious), and I require six 6.3v 250mA fuse lamps, which I found at parts-express. The ones online are actually 6.0v but that should be okay, right? Anyway I also need one more which is a 6.3v 30mA lead lamp and only 3mm in size. The closest match I could find was this, which is 6v and 35mA. The only problem is it looks like that product is discontinued. They have a 12v version, but it's 5mm in size so it's out of the question. Anyone know another source for these lamps? Shipping to Canada is a must.
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May 28, 2012 03:20
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Probably not the right place to post this, but I don't really think we have a better thread for it. This single image manages to capture what I hate so much about the Arduino "movement". Ugh.
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May 28, 2012 08:20
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The poorly waxed mustache really pulls things together.
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May 28, 2012 14:19
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My Rhythmic Crotch posted:Probably not the right place to post this, but I don't really think we have a better thread for it. This single image manages to capture what I hate so much about the Arduino "movement". That looks like a Photoshop. . . his Head. His head looks like a conglomeration of Bill Paxton, Michael Biehn, and Jason Priestley's face, hair and mustache from the movie Tombstone. I can't unsee it now, and it took me a minute before I noticed a CCT board the size of an 80's boom-box in there. Seriously, does that board use transmission tower lines as it's power source?
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May 28, 2012 14:26
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My Rhythmic Crotch posted:Probably not the right place to post this, but I don't really think we have a better thread for it. This single image manages to capture what I hate so much about the Arduino "movement". And he's still using it to just blink a god drat LED.
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May 28, 2012 15:06
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Hey, not sure if this is the right thread but on the hottest loving weekend ever my air conditioning dies. We had a guy come out because we thought it was the blower motors that had been replaced this winter. The guy thinks it's the control board, that the air filter was clogged and there was no air coming in and a coil froze up, then melted and dripped onto my control board and it needs replaced. They quoted me 550 ish dollars, to replace a loving motherboard. gently caress that, I've built computers, I can do this job. Except I can't find the loving board anywhere. I have a York or Centurion furnace and the control board seems to be an Emerson 4702G. As far as I can tell there is one website, from the 90s, that used to have this board: http://www.tek4appliances.com/product/4702G/ I'm having a bitch of a time finding out if theres a replacement board or not, or where/how I can get a hold of this board so I can replace it and get some loving cold air in here. Any help?
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May 28, 2012 18:03
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Fooley posted:And he's still using it to just blink a god drat LED. Yeah but you should see the size of the LED. It'll literally melt your skin off at 50 paces.
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May 29, 2012 04:14
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I've noticed that Arduino people care less about their application and more about the fact that they're using an Arduino to do it. That has always been why their community has rubbed me the wrong way.
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May 29, 2012 04:41
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BattleMaster posted:I've noticed that Arduino people care less about their application and more about the fact that they're using an Arduino to do it. That has always been why their community has rubbed me the wrong way. That, and I've posted about it before, but after doing one blinky LED project, they run around without a basic understanding of electronics as "makers" who "love to teach" others about what they (haven't) learned.  One of the more competent persons at a local hackerspace turned away some desperately needed ~40Ah or so batteries because "the motors were only 14A, we don't want them to overheat/overcurrent from the larger batteries!"  The MSP430 is $4.30 + shipping compared to what is now, like $25 for an Arduino? And it'll actually force you to learn a bit of C as well.
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May 29, 2012 17:35
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