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Blind people without them knowing about it
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Oct 15, 2010 04:18
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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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Make a universal remote that can simultaneously turn off all TVs within sight of a window.
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Oct 15, 2010 15:18
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When using a external crystal oscillator, what guidelines should I follow to get the values of the load capacitors? Does polarization of the capacitors (ie: using electrolytic ones) matter? If so, which way should they go?
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Oct 17, 2010 00:33
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CptAJ posted:When using a external crystal oscillator, what guidelines should I follow to get the values of the load capacitors? Does polarization of the capacitors (ie: using electrolytic ones) matter? If so, which way should they go? Do they even make electrolytics in the picofarad range? Just use ceramics. I don't know what part you're using the crystal with, but the Microchip PIC datasheets for instance list recommended capacitor values for different frequencies.
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Oct 17, 2010 05:57
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BattleMaster posted:Do they even make electrolytics in the picofarad range? Just use ceramics. I don't know what part you're using the crystal with, but the Microchip PIC datasheets for instance list recommended capacitor values for different frequencies. Oh poo poo, they're microfarads >_< No idea why I made that mistake. I was shopping for them online and must've gotten them mixed up. I only picked the electrolytic ones because I thought they were prettier. I'm a genius, I know =P I knew even less about what I was doing at the time. This could definitely be causing trouble, right?
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Oct 18, 2010 01:38
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Yeah.
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Oct 18, 2010 02:20
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I personally think that ceramic discs are the sexiest capacitor type. Edit: Here is a picture of a robot I'm working on. It's my first time working with metal so the workmanship is a little shoddy* but I'm pretty happy with it so far. I might redo the frame down the road and make it much less wide, though. *See the missing bolt? It's missing because the holes I drilled didn't line up 
BattleMaster fucked around with this message at 03:18 on Oct 18, 2010 |
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Oct 18, 2010 02:53
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So, I nearly blew another BJT transistor yesterday after switching from a lovely tiny transistor to a power transistor. The things are just limiting the current too much and getting too hot in the process. If I switch to a MOSFET, will I have better results? Looking at Mouser, I'm seeing a power MOSFET rated for resistance from drain to source at 5.3 mOhms, which should let all the current through I need. Is this right?
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Oct 18, 2010 04:05
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Exitlights posted:So, I nearly blew another BJT transistor yesterday after switching from a lovely tiny transistor to a power transistor. The things are just limiting the current too much and getting too hot in the process. If I switch to a MOSFET, will I have better results? Looking at Mouser, I'm seeing a power MOSFET rated for resistance from drain to source at 5.3 mOhms, which should let all the current through I need. Is this right? If you're the guy trying to manipulate his car's electrical system, get a relay and be done with it.  Sorry the schematic is so awful, I don't have schematic software or visio on this computer.
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Oct 18, 2010 11:52
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TacoHavoc posted:If you're the guy trying to manipulate his car's electrical system, get a relay and be done with it. Won't you want a diode across the relay?
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Oct 18, 2010 12:11
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Unparagoned posted:Won't you want a diode across the relay? Yes you would, sorry. That was a lazy attempt before work this morning.
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Oct 18, 2010 21:26
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How do you tell which component is burning up? I have been touching various components. But today I've come to the realisation that some component can get very hot and touching them isn't the best idea.
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Oct 18, 2010 22:18
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Don't be a pussy and just touch it. Most you'll lose is some fingerprints anyways. Generally if it's hot enough to lose fingerprints over the board itself will get fairly warm as well. FR-4 still conducts heat.
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Oct 18, 2010 22:24
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Zo posted:Don't be a pussy and just touch it. Most you'll lose is some fingerprints anyways.
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Oct 18, 2010 23:31
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Unparagoned posted:It's a breadbord. I currently have a nice resistor burn mark on my finger. I've had it on ice for the last few hours. I just thought there might be a better way. I dunno, maybe hold your finger over it for a second without touching it to see if its blazingly hot. I think most people over 8 have figured this out. Otherwise many multimeters support thermocouples. Or get one of those IR temp sensors.
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Oct 18, 2010 23:37
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Burn test is the best test. One time I had a breadboard set up to program a PIC microcontroller. I had a breadboard cable for my ICD3 and some jumpers plugged into it so I could plug the chip in, program it, remove it, and put it into the board I was working on. At some point I was trying to program the PIC but the ICD3 wasn't seeing it. After a few minutes of troubleshooting I smelled something burning. I touched the PIC and it burned me, a sure sign that something was wrong. Turned out that I had plugged it in one set of pins over by accident so VCC was connected to ground and an I/O pin was connected to VCC. It was so hot that it melted and permanently ruined the breadboard. After I let the microcontroller cool down I was able to program it properly, with a different breadboard of course. It still works to this day but the I/O pin that was incorrectly connected is shot 
BattleMaster fucked around with this message at 23:48 on Oct 18, 2010 |
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Oct 18, 2010 23:46
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Unparagoned posted:It's a breadbord. I currently have a nice resistor burn mark on my finger. I've had it on ice for the last few hours. I just thought there might be a better way. With resistors you should know how much current's flowing in each part of your circuit though. Then see if any resistors are close to their wattage ratings (even at ~75% of their ratings resistors tend to get fairly hot).
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Oct 19, 2010 01:49
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Anyone have experience with rework stations? In particular, I'm looking to buy this one: http://circuitspecialists.com/prod.itml/icOid/9766 I'm not too sure how interchangeable this station is with other tips/nozzles, and I haven't been able to find many reviews on the net about any rework stations at all.
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Oct 19, 2010 08:46
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ValhallaSmith posted:I dunno, maybe hold your finger over it for a second without touching it to see if its blazingly hot. I think most people over 8 have figured this out. Otherwise many multimeters support thermocouples. Or get one of those IR temp sensors. We have a thermal camera at work that is great for these sort of things. One glance and you know what's running hot on a board. They cost like 10k though so I doubt that's much help to you.
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Oct 19, 2010 13:49
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I've got this circuit but it has some strange behaviour and not too sure on why. It's a standard 555 astable circuit connected to a npn transistor connected to an audio transformer. The problem I'm having is I get really weird behaviour when I vary R3. It changes the frequency output of the 555, as R3->0 the frequency gets faster. I don't really understand why.
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Oct 19, 2010 22:13
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Unparagoned posted:I've got this circuit but it has some strange behaviour and not too sure on why. Just a guess, but what happens to your 9V supply as R3 -> 0? Is it sagging?
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Oct 20, 2010 01:11
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yergacheffe posted:Anyone have experience with rework stations? In particular, I'm looking to buy this one: Basically you only need a good soldering iron for 90% of tasks. With a cheap hot air gun, that covers like 99.5%. So just buy a good soldering iron and a cheap standalone hot air system. You'll find that if your soldering iron is excellent (like a metcal), you will need specialized tools only rarely. Hillridge posted:We have a thermal camera at work that is great for these sort of things. One glance and you know what's running hot on a board. They cost like 10k though so I doubt that's much help to you. ANIME AKBAR fucked around with this message at 04:09 on Oct 20, 2010 |
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Oct 20, 2010 04:06
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It's true, even the pro reworkers I've seen that handle $10000+ prototypes and can do everything from resistors to BGA ICs only use nice soldering irons and a heatgun. I mean I'm sure they have more specialized poo poo in some drawer but I've never seen them use it.
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Oct 20, 2010 04:12
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I'm integrating a joule thief into a larger project, and attempting to control whether it is on or off based on by toggling the supplied power using a pchannel mosfet. T10 is an nchannel connected to my microcontroller, R24 is the pulldown resistor for the output so it doesn't float. It allows me to switch Q1 with positive logic, and seems to pull down to ~0V no problem. Q1 is the pchannel control transistor, and R23 is the pull up resistor so it doesn't float. R2 is the resistor from the joule theif design, and A2 is the off-board connectors to the LEDs. I think I need T10 to run Q1 because the microcontroller and the LED system are on different buses. The LEDs run off of solar-charged capacitors, and I am hoping to use the joule thief to light them up when the capacitors are still below Vforward for the LEDs. The circuit works except I can't drive Q1 totally into saturation, not even close! I substituted a 1.5V AAA battery as VCC to do some testing, and with the gate of Q1 held at 0V, I only get .4 volts on the other side. So much for these being "...particularly suited to low voltage applications requiring a low current high side switch." (BSS84 datasheet) If I bypass Q1 with a wire, I more-or-less get the correct behavior. I actually have a bunch of LEDs, each with it's own individual low-side switch, but the joule thief seems capable of driving the low-side switches on, even with the gates held low. I haven't worked out what's going on there, but I was expecting to need a high side switch (master on) and a low side (LED select) anyways for power efficiency, so it's fine as long as I can figure out what to do with Q1 to get it to operate correctly with low VCC values. I would like to run the board sub-1V, but can live with 1.5V or so as the minimum acceptable value. Does anyone have any suggestions? Right now the pullup/down resistors are 47K, and I would be happy using a PNP transistor or any other solution people might have, I just don't know of any components with extremely low Vthresholds. Is the value of R23 too low maybe? Delta-Wye fucked around with this message at 17:15 on Oct 20, 2010 |
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Oct 20, 2010 17:10
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Thanks for the feedback on the rework station guys. I guess for now I'll be going with the CSI-STATION1A as my iron. It's a knockoff of a Hakko 936, so it seems it'll do for the small hobbyist electronics work I'll be doing. That, and I can't seem to find a middle ground between the Hakko936/Weller WES51 range to a Metcal. Do you guys have any suggestions on which hot air stations to look at?
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Oct 20, 2010 19:28
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TacoHavoc posted:Just a guess, but what happens to your 9V supply as R3 -> 0? Is it sagging? It become a square wave with say a magnitude less than 0.5V. It seems like a small change that I cant't see why it would effect the 555 frequency by the massive magnitude it does. But I'm fairly clueless about electronics in general. Edit: Oops, I was going by memory, check it out and there is a massive change on the 9V supply, it's a square wave going between 9V to 4V or so. So I guess that is going to have a major impact. Now I need to now how to stop it. FSMC fucked around with this message at 20:51 on Oct 22, 2010 |
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Oct 20, 2010 19:30
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Also, an LED question. I need some common anode LEDs, and these seem to fit the bill: http://cgi.ebay.com/New-Product-100X-SMD-SMT-PLCC-4-RGB-LEDs-800mcd-F-Ship-/250532306867#ht_3078wt_905 They are labeled as "common anode" in several places on the page, but the diagram is clearly common cathode. The LEDs appear to be common anode looking at them - the single T3/4 LEDs I have on hand have the 'well' side on the cathode, and the wire bond runs to the anode. This seems to match the picture, indicating the descriptions are correct and the diagram is wrong. C/D? Don't want to waste a bunch of money on useless SMD leds 
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Oct 21, 2010 19:29
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Delta-Wye posted:The LEDs appear to be common anode looking at them - the single T3/4 LEDs I have on hand have the 'well' side on the cathode, and the wire bond runs to the anode.
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Oct 22, 2010 14:09
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Unparagoned posted:Edit: Oops, I was going by memory, check it out and there is a massive change on the 9V supply, it's a square wave going between 9V to 4V or so. So I guess that is going to have a major impact. Now I need to now how to stop it. What's happening is that you're sucking current equal to (9V/(resistance of transformer coil+potentiometer resistance)) to ground. The transformer is probably a low resistance, making your current draw really high as your potentiometer resistance approaches zero. Your power source (I'm guessing a battery) can't deliver that much current, so the output voltage is sagging. To solve this problem, you could try putting a current-limiting resistor between your power supply and the node that the diode cathode and the transformer are connected to. What are you trying to accomplish with this circuit? It seems like if you were trying to vary the output, you'd be manipulating the voltage divider on the other side of the 555.
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Oct 23, 2010 01:09
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TacoHavoc posted:What's happening is that you're sucking current equal to (9V/(resistance of transformer coil+potentiometer resistance)) to ground. The transformer is probably a low resistance, making your current draw really high as your potentiometer resistance approaches zero. Your power source (I'm guessing a battery) can't deliver that much current, so the output voltage is sagging. That sounds like what's happening and makes sense, I'm drawing too much current. The circuit isn't actually the circuit I'm using it's a slightly modified version to illustrate my problem. Basically I want a circuit which will input a fixed frequency square wave at different voltages to the transformer. The transformer has a very low resistance, but I want most of the voltage across the transformer. So the resistors on the transformer side had to have a low value but then then the resistors were heating up. So I was thinking I don't want any energy to be wasted heating up these resistors, so removed them. Wouldn't your current limiting resistor have most of the voltage across it rather than the transformer? Wouldn't manipulating the voltage divider the other side of the 555 just change the frequency rather than magnitude? Is there a way to limit the current but also keep most of the voltage across the transformer? FSMC fucked around with this message at 15:35 on Oct 23, 2010 |
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Oct 23, 2010 15:24
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You might just want to switch to a lead acid battery that can supply the current needed. I don't think there's a way to limit current without causing a voltage drop ala Ohm's Law. Unless it involves some inductor wizardry which I suck at.
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Oct 23, 2010 18:28
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You need to find out what the magnetising inductance of your transformer is. That determines the effective 'resistance' of your transformer at a given frequency. Also you are magnetising the transformer in one direction only. When you turn the BJT off, the magnetising current circulates through that anti-parallel diode, and the voltage drop across it is the only thing which is returning (relatively slowly, compared to the 9 volts that was being applied to it before) the core flux of the transformer to zero. I don't know where you got this circuit from but it doesn't look like it's good for much. Look up forward converters. What is it that you are trying to do exactly?
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Oct 24, 2010 09:30
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catbread.jpg posted:You need to find out what the magnetising inductance of your transformer is. That determines the effective 'resistance' of your transformer at a given frequency. Also you are magnetising the transformer in one direction only. When you turn the BJT off, the magnetising current circulates through that anti-parallel diode, and the voltage drop across it is the only thing which is returning (relatively slowly, compared to the 9 volts that was being applied to it before) the core flux of the transformer to zero. I don't know where you got this circuit from but it doesn't look like it's good for much. All I know about the transformer is that it's a 1.2k ohm to 3.2 ohm transformer. The 1.2k ohm is suppose to be the primarily, but I'm using it in reverse. There is no spec sheet or anything else. http://www.maplin.co.uk/Module.aspx?ModuleNo=3709&C=49287 The circuit is basically a tens machine. I've looked at some other tens machines, it seems they deal with the supply oscillating by using a zenner diode, resister and transistor to limit the voltage to the circuit to 5V. This allow a full 5V drop across the transformer, which I guess is enough. Also there is a capacitor used to help supply the current for the spikes, which helps smooth out the battery issue. Could you explain a bit more about the magnetising in one direction only, I'm not sure what you mean. My limited understanding is: The standard state would have the BJT off, then on for a short period. The voltage drop when it's turned on would allow current to flow. Then when the BJT is tuned back off, the transformer would induce a high voltage and then current would flow through the diode. Ahh, so do you mean the up and down would be asymmetrical. From the output I'm getting I don't think it's an issue. I did some calculations, hopefully they are right. BTJ on, I=V/R*(1-e^(-Rt/L)). BJT off, I=V/R*e^(-Rt/L). So that makes it seem symmetrical. I'm not too sure about how I dealt with it when BTJ when off. I assumed that the fact it was connected to the 9V didn't matter(reasoning was everything is kind of relative).
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Oct 24, 2010 13:02
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Just checking in, need some advice on a soldering station. I have used the cheapo radio shack units many times, I have about 20 of them I am sure, just can't find them which is probably a good thing. I need something that is capable of working on laptop motherboards (for soldering/desoldering stuff like AC jacks, etc). I generally don't work with anything tiny, so what would be a good kit for me? I would prefer to stay under $100.
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Oct 27, 2010 14:04
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mAlfunkti0n posted:Just checking in, need some advice on a soldering station. There are some soldering stations on sparkfun http://www.sparkfun.com/commerce/advanced_search_result.php?keywords=soldering&x=0&y=0&search_section=products Personally I like Weller stations as it's what I've used all throughout University and thats what they buy. But those can be a tad pricey. But finding a good soldering station makes your life so much easier in the long run. http://canada.newark.com/jsp/search/productdetail.jsp?SKU=92C1414&N=0 This is the one I have in my lab and I love it, I've never run into any problems with it what so ever.
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Oct 28, 2010 05:28
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Zampano posted:http://canada.newark.com/jsp/search/productdetail.jsp?SKU=92C1414&N=0 These are what my adviser's lab uses. For some reason, they seem to break pretty often (three in the last three months). Also, their normal tips work horribly with lead free solder. Other than that they're quite good.
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Oct 28, 2010 05:53
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If you're soldering for yourself (instead of at work where it's banned) there's no reason to EVER use lead-free solder. Literally the worst.
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Oct 28, 2010 05:55
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mAlfunkti0n posted:I generally don't work with anything tiny, so what would be a good kit for me? I would prefer to stay under $100. You absolutely cannot go wrong with a Weller WES51 http://www.amazon.com/Weller-WES51-Analog-Soldering-Station/dp/B000BRC2XU
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Oct 28, 2010 06:30
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Hypnolobster posted:You absolutely cannot go wrong with a Weller WES51 These are good. I have a WLC100 at home and it works acceptably well for the price.
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Oct 28, 2010 06:54
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