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Portable skin cancer booth. Maybe a cool night-vision camera flash? That's still drat risky wrt eye safety though.
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Oct 15, 2010 08:07
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Multimeters usually output something like 1.6V on the diode tester... high end models probably have a higher voltage options. -- I know this is a long-shot but does anyone know a way of getting NEC service manuals? I've been calling all day to their German headquarters as well as the Swedish repair centre, and they plain refuse to send them to outsiders. If anyone has any connections or something like that and could get me the schematic PDF for the MultiSync V921 Model N903 it would really get us out of a tricky situation here. There is one site that has the V921-1, this is a different board, googling results in a PDF of the service manual but the schematics are too small to read so it's useless. We use CRT monitors to train students in fault finding, and we thought we had the correct manual, but it was for a different system board, without this we're pretty much SOL...
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Nov 8, 2010 14:39
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The Scientist posted:According to this, the one and only google result for ext:pdf MultiSync V921 N903 Thanks, I've sent them an email, though at this point I'm not expecting much... If this doesn't turn out, we'll have to look into other devices to teach with, any suggestions for something roughly as complex as a CRT which is also possible to get schematics for? Obviously anything surface mount is out...
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Nov 8, 2010 23:05
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randyest posted:I work for NEC Electronics (now Renesas Electronics) in a different division (semiconductor design,) but I have pretty extensive intranet access and some decent connections with the display group (which, as you might guess, has pretty much completely transitioned to LCD design and support these days.) Thank you so much, unfortunately I doubt any of the people I talked to actually tried to find it though. There are some other people here in Norway who might have worked on monitors, but it's out of my hands now. At this point I doubt we'll be able to use the monitors so we're mostly looking for a replacement that includes complex analogue circuits, switch mode power supply etc. like a CRT does. The only appropriate devices we have are a few audio amplifiers and CD players, but they're simple enough that anyone actually interested in fault finding will know them like the back of their hand in a few weeks. Any ideas there would be greatly appreciated  standardtoaster posted:I'm looking for an entry level oscilloscope (<$100) on craigslist. Can someone give a rundown of brands? BK Precision, Kikusui? 60MHz, 35MHz? I know nothing about oscilloscopes. Why do I need one? I probably don't, but I want one and am going to learn how to use it. Oscilloscopes are fun to play with, I would recommend finding a 20+ MHz analogue CRT scope, they should be plentiful on the used market and far more robust than any DIY digital solution. Over here Leader is commonly found used, but Tektronix, Agilent/HP and Philips-Fluke are likely better. I'm pretty pleased with my HP 1740a 100 MHz but it's not exactly compact and uses some custom ICs for important functions that will be difficult to replace. I used a PM3350 in school, that was good too but probably still expensive. longview fucked around with this message at 13:24 on Dec 8, 2010 |
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Dec 7, 2010 18:19
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If it's DC coupled internally even a blown input stage could destroy everything all the way to the outputs. If the transistors are bipolar you can measure if they work pretty easily with a diode tester and the base-emitter junction. Though I wouldn't do this without a good sized pile of spare transistors...
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Dec 11, 2010 00:08
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AnomalousBoners posted:I talked to a well learned man about this today and he suggested getting an analog multimeter to test the caps. The reason being it allows you to see a quick spike and then the discharge... Though apparently we have cap testers here at school....so yea I will probably be bringing them in here. Also yes these are polarized "can type" caps. In general when measuring large caps with a diode tester you'll see the voltage start at 0 and then increase until the cap is charged to whatever voltage the tester uses, often 1,6-2V. If you then reverse the polarity it will start at -something, cross zero and move up. I think most capacitor testers work the same way, charging it up and measuring the time it took. I saw a capacitor in a TV PSU once where the capacitance was way down but it worked otherwise, in that case it was a filter cap for the secondary of the stand-by supply. Since it wasn't filtering properly the power was very unstable and noisy, which made the feedback system shut it down after a few seconds.
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Dec 13, 2010 22:17
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I think most opamps connected in that configuration will have a nearly infinite input resistance, at least for FET based models.
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Dec 22, 2010 21:17
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ante posted:I'm going to have access to a woodshop for the next little bit, so naturally I'm going to be making a clock from scratch that contains a shitload of blue LEDs. As mentioned you'll have to multiplex them, most battery powered LEDs use a PWM controller to allow dimming and significantly save power by only having them lit for short intervals as well.
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Dec 29, 2010 12:17
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I have two transformers from UPSes, approximately 450W output. Normally they transform 230V to 24V and in reverse, would I be farely safe using the 110V primary winding to get 48V? Obviously I'll try it using a vari-acc instead of just wiring it up. I also have from the UPSes two sets of approx 15x 50/60V 50/60A N-channel MOSFETs. I was thinking about building a lab power supply with them, if I could get 48V from them I could probably build a 0-40V (0-30V also acceptable) or more and upwards of 10A. However even the most basic heat calculations show that with my power transistors and heatsinks the junction temperature would be enough to acheive fusion, so some kind of switch mode operation would be advantageous. Does anyone have any ideas for a controller/reference design for a switch mode step down converter, without using a transformer preferably (the mains transformer is heavy enough)? I'm also wonder if it might be more useful to build 2-3 slightly smaller supplies instead of the one very high current one, how would the controllers react to being connected in parallell, would they balance themselves assuming the voltages match exactly?
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Jan 2, 2011 09:12
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ANIME AKBAR posted:You mean you want to put 240V into just one primary winding (instead of both primaries in series) in order to double the output voltage? No, that will almost certainly saturate the transformer. Ok, good to know. I'll try to find the datasheets and unless they specifically say it won't destroy it I'll have to use both transformers for one project. I don't suppose connecting the live wire to both ends of the primary, then the centre tap to ground would work any better? --- After reviewing the project requirements I've decided against building my own SMPS, as I have nowhere near the experience needed to do so without breaking lots of things and starting small fires. My plan now is to get the 48V input, rectify and filter, then use something like the LM2678 buck controller, the WEBENCH tool looks like it will help me select the proper component values. I'll probably make two of them, so I can have two separate output voltages (1.2-~37V) at 5A. In addition I was thinking about using a few 78 series regulators to make some standard voltages (3.3, 5, 12 and 24V 1-2A each) in addition to that. Assuming I get the LM2678s to work it should be smooth sailing.
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Jan 2, 2011 19:22
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Not an Anthem posted:I don't know anything about electronics so treat me with kiddie gloves. In school we used standard 1k 0.6W resistors to discharge capacitors, that worked fine. Those capactitors are all low voltage anyway so there's no real risk of electrocution as long as you discharge the primary (150/250V) capacitors before starting.
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Jan 2, 2011 19:24
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Delta-Wye posted:I've been wanting to build a power supply around this circuit: Cool, I had considered doing something like that but thought it would be too much work to make them work together. That looks like it could be used with the 5A LM2678, and some more cooling for the MOSFET pretty easily.
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Jan 3, 2011 12:44
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No doubt, my plan for now is buy the parts to make 2 adjustable and 12 and 5V models, once those are working I'll look into adding a linear output stage.
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Jan 3, 2011 20:33
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Not an Anthem posted:I replaced the capacitors and the monitor works like brand spankin new. I don't use Amazon but I do know EEVBlog has done several multimeter reviews: http://www.eevblog.com/2010/04/14/eevblog-75-digital-multimeter-buying-guide/ http://www.eevblog.com/2010/06/04/eevblog-91-50-multimeter-shootout/ E: I disagree about auto ranging though, I find manual ranging to be quicker in a lot of circumstances, especially since cheaper auto ranging is slow. longview fucked around with this message at 21:53 on Jan 3, 2011 |
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Jan 3, 2011 21:24
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Mill Town posted:There's no universal treadmill wire color code, so I really can't say what's what there. Try googling for a service manual or a schematic. Looks like it's time to DIY a high powered inverter! 
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Jan 5, 2011 23:21
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A second microcontroller behind the obvious first battery and controller. And in sci-fi land, an old TV flyback generator connected to the case so anyone touching it would get shocked.
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Jan 6, 2011 11:38
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IsaacNewton posted:*blank stare* The problem here is that flash units have a HUGE current draw when charging. A rechargeable ni-mh AA cell can supply something like 10A to a low impedance load. Linear regulators stop at about 5A for simple circuits, heat shouldn't be a problem since it's only at max current for short periods.
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Jan 13, 2011 10:57
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Guessing the aspergers team-member decided the CMOS 4000 series is better than any µController.
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Jan 17, 2011 13:59
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Any recommendations for something really simple to turn an output on or off from a serial input? I want to make my old CRT switch between 4:3 and widescreen mode without me manually changing a switch or the settings. The pin to control it needs around 5V (75 ohm) to enter widescreen mode. It's connected via a VGA-SCART cable. So my plan is to find some way to toggle an output, build a cheap transistor driver and write some C# code to send the serial signal on resolution change. Can I do this with some simple IC instead of dealing with a large µController?
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Jan 19, 2011 09:41
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SolidElectronics posted:You can probably use the DTR line connected through a diode to a voltage divider (or whatever transistor driver you're planning). I don't know much about controlling a serial port with a PC, but there should be a way to toggle it. Neat, that line looks perfect for what I need, it looks like DTR control is built into the IO library in .NET! As for the parallel port: I actually had one hooked up for testing but the only way to control it directly from Windows 7 seems to be via third party drivers, otherwise it's limited to data I/O and that didn't work with the 64-bit Windows on my desktop. I'd have done more experimenting but the computer is an old gaming laptop so no serial/parallel (will order a USB adapter).
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Jan 20, 2011 21:17
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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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We just had a county wide power outage (a 420kV line snapped severely reducing capacity) for a few hours. In part because until they can repair the power line they may have to cut power again I've decided to get a UPS. The problem is a 750VA UPS in my price bracket will only have the batteries to last about 5 minutes under full load. I do have a stack of SLA batteries, approximately 750Wh across several batteries, what do you suppose would happen if I connected them all in parallell to the UPS, instead of the normal 7.2 Ah SLA? Aside from the danger of a very large lead acid battery pack, should I have any problems with the UPS?
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Feb 17, 2011 13:44
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I suspect the normal method is to digitize the whole signal and then do a fourier transform on that digitally. I've never done it, but I suspect you'll need a controller aimed at DSP applications to do it easily.
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Mar 10, 2011 14:37
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Delta-Wye posted:Have you considered 741s? I hear they are all the rage these days I prefer common emitter amplifiers, with 2N2222As
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Mar 10, 2011 21:09
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Speaking of AC-DC supplies, the LT1083 datasheet has a nice schematic for a regulated linear high power supply using SCR rectifiers to reduce the input voltage: This looks like it would blend some of the advantages of SMPS+linear output stage without the overhead of doing SMPS design. Obviously the rectified waveform will be pretty distorted so it looks like extensive filters are needed.
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Mar 20, 2011 20:32
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therunningman posted:I have a +/-12V system, and I want to run an IC in it at +/-7.5V. Are you going to draw a lot of current? If it's an opamp or similar you could use 78 and 79 series regulators, they are available for 8V, 100mA to 1A, the 78 series regulates positive and the 79 negative voltages. Part numbers LM7808 and LM7908.
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Mar 26, 2011 19:19
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Also Atom chips use a lot more power than a microcontroller so if it's for a battery powered application you'll have a lot of problems. Do the arduino over usb thing!
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Apr 1, 2011 08:14
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Fat Turkey posted:ohgodohgodohgod Is this a good starting Arduino board? I have that one and it's pretty OK. It's designed to interface with the arduino expansion cards but with a couple of wires connecting it to a breadboard is no problem.
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Apr 16, 2011 17:46
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Also there are cell modems that use standard command sets, I found one in the trash which supports voice calls, GSM modem and SMS features, the latter two over the serial port. E: A Wavecom WMOD 2, I'm actually planning to do something similar only monitoring network and power at home. longview fucked around with this message at 17:17 on Apr 17, 2011 |
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Apr 17, 2011 17:12
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Hi all, my current project is to build an LM3886 based amp to replace my 20W mono amplifier I use with the TV. I ordered the dual mono kit from Chipamp.com for the actual amplification, and now I've been working on the input selector/control system. My goal is to have 3 standard inputs and USB. To get USB I ordered an Alien DAC kit which should be here in a week or two, I plan to power this from an 8V regulator (board has an internal regulator as well). Another design goal is excellent SNR and simplicity, my current plan is to use signal relays to toggle inputs, directly driven by 12V via a 4-way selector. The relays I ordered have 12V 17mA, the ratings for the selector knob only say 500V for up to 1 minute. Should I continue with the direct drive design or should I put in some drive transistors and protection diodes? Probably the most important design feature is support for headphones, so my plan is to use more relays to switch the output from speakers to the headphone jack (with 20R in series), and also switch to a second volume control. I also want a separate "trim" control for each input (some sources are louder than others), my plan is to just connect this like a normal volume and chain that to the main control, would that be problematic wrt. impedances/loss? I've ordered a 10x pack of 10k log stereo potmeters so I'll be using those. It doesn't look like the amplifier module has any DC blocking caps, so any recommendations for what types would be best suited are appreciated. Lastly I was wondering if there would be any disadvantages to using coaxial cable (RG-6) for internal signal wiring, I have a large spool of flexible cable so if I can use that instead of buying some special audio cable I'd prefer that. If that was hard to follow I have some schematics here:  Input selector with volume controls. There's also a relay and switch for aux send, that's to support an equalizer I have lying around.  Block schematics for the amplifiers + main PSU and the design for the USB+relay PSU (already built). I also have a time-delay relay in there to give the system time to stabilize, I'll consider removing this after I've built it. The mains switch will be front panel mounted.  Basic mockup of the front and rear panels. My reason for powering the leds from so many sources is to allow me to diagnose potential failures in power supplies based on which LEDs go dark. longview fucked around with this message at 21:05 on Apr 29, 2011 |
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Apr 29, 2011 20:36
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Master Stur posted:
Careful, I think intel is on to you guys: http://www.youtube.com/watch?v=QDoLGOokQRg (no embedding)
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May 6, 2011 09:16
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I've been trying to track down a ground loop inside the amplifier I built, in the end I was given a transformer+chassis which also had a nice preamp with input selector tone control etc. (Yes the internal wiring is a slight mess in that picture, it's not done yet!) It looks like all the input signals go through that IDE cable (every other pin is ground), then input selector volume etc. then on to the rest of the system. Unfortunately when there's no input signal it looks like the opamp (or something close to it) is causing a ground loop noise to be added to the signal (predominantly small spikes at 100 Hz). It's not too noticeable with speakers but it used to be really bad with headphones (up to 100mV peaks, after amplification by the power stage). When I disconnect the pre-amp and use any other source there is no ground loop. I managed to reduce the amplitude by jumpering across all the different ground points on the board (terrible layout) which eventually did make a slight difference. I also replaced the opamp with a worse one (more hum) and later an LT072 (have an OPA2134 on order) which did supress the hum slightly more but I think it's masking it in noise as well. The preamp looks like it's a normal opamp->bass->treble->balance->output design, the on-board supply is a 7912+some kind of transistor based system both of which seem to provide clean power to the rest of the board, but scoping with ground at one end the ground plane on the other appears to contain small spikes like on the output. tl;dr: Anyone have any tips for trying to track down ground loops inside a circuit?
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May 11, 2011 10:07
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nobody- posted:Thanks for the link! I've had one for almost a year now, it's alright, auto ranging is slow especially for resistance but otherwise nothing in particular wrong with it as far as I can tell.
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Jul 18, 2011 15:42
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http://benkrasnow.blogspot.com/2011/06/tutorial-electrical-impedance-made-easy.html That circuit seems like it might work for you? Depending on the frequency you might need a fairly large capacitor is all.
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Jul 24, 2011 10:43
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It also seems unnecessary to use both phases, a Schottky diode single phase rectifier + filter capacitor can't possibly be more complex than some kind of diode-capacitor circuit or transistor/thyristor driver circuit. If the capacitor size is a problem then you'll need a higher voltage for a bridge rectifier, what is your voltage source by the way? You'll need to account for up to 10% voltage drop if it's powered by mains. Another option is a full-wave rectifier and a centre tap, or some kind of PWM transistor drive but I assume you have a good reason for not doing that already. E: Also my calculations seem to indicate that assuming the cap can charge to the full rectified voltage you'd need something in the ~3-4mF range. longview fucked around with this message at 17:57 on Jul 24, 2011 |
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Jul 24, 2011 17:45
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You still haven't said what the frequency is, for 3-4mF I assumed the LED acted like a 6 ohm resistor and needed to power it for 16 ms (i.e. one half-cycle of 60 Hz) starting at about 8V and dropping to 4V. A very large capacitor will definitely take a long time to charge in this setup since it can't pull a large startup current. If you build a full wave rectifier you might get away with something significantly smaller since the time the capacitor needs to supply power decreases and the higher effective frequency will allow a larger ripple voltage.
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Jul 25, 2011 15:58
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I've used Proteus since version 6, using my license from school. It's pretty simple to use, works fairly well but it seems to work better at real time simulations than running for specific intervals, it's probably possible to use it more like SPICE though. Also licenses are tiered so my license doesn't let me simulate certain MCUs (otherwise it could load compiled code and simulate), I also can't use spectrum analyzers. Over all it's pretty good to use for simple designs but perhaps lacking for high end development in my experience.
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Sep 14, 2011 20:37
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Slanderer: What kind of opamp do you recommend for general use that's more modern? I've got a couple of TL072s and LM358Ns which seem pretty decent for the price. ole_bjorne: for intro to electronics and Arduinos, P2N2222, 2N7000 are specific perfectly acceptable transistors, and maybe some shift registers if you want a lot of outputs. longview fucked around with this message at 21:11 on Sep 14, 2011 |
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Sep 14, 2011 21:07
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Oneday for Life posted:I'm doing a little project for fun before I head off to boot-camp, so I don't have a lot of time to learn all the details of electronics before I go. I've got a good idea of what I want it to do, but I'm hoping I can get some good advice here. It can be done in several ways, the 30 second on-state can be done with a MOSFET+RC filter, triggering on every other switch-press can be done with digital logic like flip-flops, counters, or any number of analog circuits. If you have a microcontroller it'll be much easier to prototype and test a project like this in code before designing a simpler circuit to replace it, like what happens if the cat manages to enter or leave without triggering the sensor?
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Sep 18, 2011 19:23
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| # ¿ May 5, 2024 13:46 |
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I was wondering if anyone here is familiar with Citronic mixers and other PA equipment, I've got a "PSU 461" (+-15V 400mA) that goes with mixers and it's got some inputs labeled Deck Start that seem to connect to some ICs and Triacs on the primary side of the PSU. Anyone have any idea what they might be for? I'm thinking maybe some kind of soft start or extra regulation but the supply works fine with the inputs unconnected. Also, I'm going to use the PSU to power a LME49600 headset amplifier I'm building, can anyone recommend some freeware Veroboard or strip-board layout tools? It won't be a hugely complicated circuit but having some idea where to put the components will help a lot for getting a decent layout.
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Sep 22, 2011 14:37
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