Electrical Engineering V3 - Developers

The board I'm laying out right now, smallest thing is SOIC or SSOP, since I want it to be beginner-friendly if someone runs into the designs, but I'm not afraid of TQFP, and I'll be using them in the future for something. Passives, I don't like 0402, but if you've got a proper PCB instead of something that's been milled out of a copper sheet and has no resist, I can do that.

I'm getting a printer to salvage, any objects inside of it which I should be carefull with?

[QUOTE=scratch (nl);48087610]I'm getting a printer to salvage, any objects inside of it which I should be carefull with?[/QUOTE] Laser printers have a high voltage low current generator (fun), should be safe enough just beware of high voltage caps if there are any. Try do it outside to avoid toner / ink going everywhere.

Get all the motors. If it's a scanner/printer combo try to take the scanner out in one piece since that's got a linear rail inside it.

DISCLAIMER: I'm a fucking moron. So I just got burned. I was playing with an LCD screen and arduino and the connections to the LCD and breadboard weren't working that well, so I thought "hmm better solder it!", but I have no iron. So, stupid me started some deductive reasoning. Thomas Edison chose a carbon filament for the light bulb because it burned hot and bright without melting or breaking, right? So, carbon must be a good and strong resistor! the most common useable form of graphite is a pencil, so I reasoned I could make a soldering iron out of pencil graphite! I didn't want to start with too high a voltage, so I just got a USB cable and used the vcc and gnd, which I know to be 5v only. So I connected it kinda like this: [code] Graphite ==*=====*== | | + | | - | | ------- 5v| USB | gnd | | \_____/[/code] where * denotes the connections of the wires on the graphite. I felt it, and it started to get warm! I was pretty excited, so I went to show my girlfriend, when the graphite broke. I thought "No problem! I'll just hold it together!" Putting my index finger on the connection between the ground and the graphite, and my right hand on the positive wire, I touched the two ends of the graphite together and now I have a graphite stick-shaped scar on my left index finger So can you guys tell me exactly what happened? Was it my body's resistance that allowed the graphite to get up to such a high temperature? Or does the heat just grow at an exponential rate? (going from warm to burning hot so quickly)?

Someone far smarter than me can go into why you got an electrical burn, but I will point out that graphite electrodes are used to smelt aluminum.

An inefficient 2.5W soldering iron would be the most pathetic soldering iron known to man, I sometimes have trouble heating up massive heatsinks connected to ground planes with my 60W station.

[QUOTE=Cakebatyr;48091993]Someone far smarter than me can go into why you got an electrical burn, but I will point out that graphite electrodes are used to smelt aluminum.[/QUOTE] I wouldn't say it's an [I]electrical[/I] burn, technically speaking. The graphite/wire interface got one though. Graphite has really low resistance iirc, so you were effectively shorting the power supply. However, at the connection between the wire and the graphite the resistance was likely [B]much[/B] higher over a tiny distance, so that's where almost all of the energy ended up dissipating. lots of energy & small area => lots of heat In addition to being a good conductor, graphite can also be a fairly good heat conductor at [URL="https://en.wikipedia.org/wiki/List_of_thermal_conductivities"]25-470 W/(m*K)[/URL]. (Though what's in pencils probably has a slightly different, possibly higher conductivity.) At the higher end that's a lot more than most metals have, so you were hit by practically all the heat emitted at the contact location, but spread out over the contact surface between your finger and the wire/graphite. (The burn may actually have been worse over a smaller area if this wasn't the case.) USB is [I]supposed[/I] to give 2.5W at most (and it may have to be unlocked via request to the bus), but at the small area that may have been enough. It's also possible that (especially cheap) USB wall chargers may deliver high currents without proper request though. (I have one where seemingly only the charging wires are present in the cables and it's still fast. I think it still roughly matches the specification because it can't charge well multiple devices at the same time.) USB 3.1 can deliver up to 100W under certain circumstances, so I suggest you don't mess around with that once you get such a charger :v: [editline]1st July 2015[/editline] The reason graphite is used as electrodes for aluminium smelting is that they don't melt even at very high temperatures. The heat conductivity also drops a lot with temperature (though more in graphene I think), and [URL="http://link.springer.com/article/10.1007%2FBF01135029"]the electrical resistance increases linearly after 1000°C[/URL], so proboardslol wasn't really wrong about light bulbs. It just doesn't apply if the filament isn't already at a few 1000 degrees :eng101:

RS Components are pretty amazing, my Raspberry Pi's SD card slot failed, I think manufacturing issue, contacted their online chat thing and I'm getting a replacement, pretty pleased :)

[QUOTE=Tamschi;48092432]I wouldn't say it's an [I]electrical[/I] burn, technically speaking. The graphite/wire interface got one though. Graphite has really low resistance iirc, so you were effectively shorting the power supply. However, at the connection between the wire and the graphite the resistance was likely [B]much[/B] higher over a tiny distance, so that's where almost all of the energy ended up dissipating. lots of energy & small area => lots of heat In addition to being a good conductor, graphite can also be a fairly good heat conductor at [URL="https://en.wikipedia.org/wiki/List_of_thermal_conductivities"]25-470 W/(m*K)[/URL]. (Though what's in pencils probably has a slightly different, possibly higher conductivity.) At the higher end that's a lot more than most metals have, so you were hit by practically all the heat emitted at the contact location, but spread out over the contact surface between your finger and the wire/graphite. (The burn may actually have been worse over a smaller area if this wasn't the case.) USB is [I]supposed[/I] to give 2.5W at most (and it may have to be unlocked via request to the bus), but at the small area that may have been enough. It's also possible that (especially cheap) USB wall chargers may deliver high currents without proper request though. (I have one where seemingly only the charging wires are present in the cables and it's still fast. I think it still roughly matches the specification because it can't charge well multiple devices at the same time.) USB 3.1 can deliver up to 100W under certain circumstances, so I suggest you don't mess around with that once you get such a charger :v: [editline]1st July 2015[/editline] The reason graphite is used as electrodes for aluminium smelting is that they don't melt even at very high temperatures. The heat conductivity also drops a lot with temperature (though more in graphene I think), and [URL="http://link.springer.com/article/10.1007%2FBF01135029"]the electrical resistance increases linearly after 1000°C[/URL], so proboardslol wasn't really wrong about light bulbs. It just doesn't apply if the filament isn't already at a few 1000 degrees :eng101:[/QUOTE] so where I had felt it in the middle of the graphite tube, the tube was warm, but where I grabbed it at the wires, the tube was hot?

[QUOTE=proboardslol;48093776]so where I had felt it in the middle of the graphite tube, the tube was warm, but where I grabbed it at the wires, the tube was hot?[/QUOTE] Most likely. It would have cooled enough after breaking that you didn't hurt yourself immediately when grabbing it, but the the restored circuit quickly heated it again there (and probably in a few other places, which you may not have noticed. The other graphite/wire interface and the point where the graphite parts touched are likely).

Anyone know of a type of sensor that changes resistance in response to compression? I.e. Physically like a spring that you can compress, but its resistance changes like a flex sensor.

[QUOTE=LoneWolf_Recon;48096209]Anyone know of a type of sensor that changes resistance in response to compression? I.e. Physically like a spring that you can compress, but its resistance changes like a flex sensor.[/QUOTE] A strain gauge.

Where can I get started learning ARM programming? I feel I'm competent enough with arduino and I need more power for a new project I'm working on.

[QUOTE=papkee;48098610]Where can I get started learning ARM programming? I feel I'm competent enough with arduino and I need more power for a new project I'm working on.[/QUOTE] I like TI's boards, you're in the States so shipping from the TI eStore should be reasonable for you. The MSP432 is very new, it's a Cortex-M0 with the same peripherals as an MSP430 more or less, designed for low power. They also have the Tiva stuff which is faster and higher power. There may be cheaper boards from ST or NXP or whatever, but I've never had issues getting CCS to run on Windows and the TI boards aren't too expensive anyway.

[QUOTE=papkee;48098610]Where can I get started learning ARM programming? I feel I'm competent enough with arduino and I need more power for a new project I'm working on.[/QUOTE] You don't learn how to code for one specific platform. If you know C (or any other language) you can code for whatever you want, be it a virtual CPU, x64 or something entirely different.

Finally got the values for my teletypes telephone dialer circuit. 330 Ohm for the resistor and 200v 0.47uf for the capacitor. Hopefully this will be completed before the end of the month, fucking finally. :dance:

The compiler toolchain and libraries are something entirely different though, what exactly do you want to program? [editline]2nd July 2015[/editline] Merge. :(

[QUOTE]Where can I get started learning ARM programming? I feel I'm competent enough with arduino and I need more power for a new project I'm working on. [/QUOTE] Why not try the raspberry Pi's ? while i have not tried the aspect of programming the actual cpu,nor know anything about it, i do believe you could do it.

I want something a bit more embedded than Pi. It's a great platform for some things but I'm looking for something I can integrate into a project more fluidly. I figured ARMs were programmed in some form of C, but what I wanted to know more of was how different it is from coding AVRs. In terms of configuration, inputs/outputs, basically how to migrate my arduino knowledge over.

[QUOTE=papkee;48098818]I figured ARMs were programmed in some form of C, but what I wanted to know more of was how different it is from coding AVRs. In terms of configuration, inputs/outputs, basically how to migrate my arduino knowledge over.[/QUOTE] Programming for different architectures really isn't different unless you're doing something really low level, like writing a bootloader that actually requires you to use architecture specific stuff like some registers, virtual memory, segmentation or whatever (or if you're using assembler). That said, even programming the same CPU can be radically different based on approach. You first have to decide what CPU you want to program before asking how you can program it. [editline]2nd July 2015[/editline] That said, there's Arduino Due that has an Atmel SAM3X8E ARM Cortex-M3 CPU on it. You can program it using the default Arduino IDE.

I don't really want the Due because I'd like to be able to migrate the project to a barebones chip. Let's just say for example I wanted to use the Cortex-M0, like atmel's SAM20E. Can I program it through the arduino IDE and what programmer do I need to flash it?

[QUOTE=pentium;48098753]Finally got the values for my teletypes telephone dialer circuit. 330 Ohm for the resistor and 200v 0.47uf for the capacitor. Hopefully this will be completed before the end of the month, fucking finally. :dance:[/QUOTE] You really need to get yourself a set of resistors and caps, I always keep a bunch of common values on hand to avoid delay.

[thumb]http://i.imgur.com/KFkuhkd.jpg[/thumb] Disassembled my old printer, found some useful stuff inside.

See if you can pull out the motor driver chips as well, especially useful.

[QUOTE=LoneWolf_Recon;48102652]See if you can pull out the motor driver chips as well, especially useful.[/QUOTE] These chips are pretty much impossible to solder out of the PCB for me, too small.

[QUOTE=papkee;48099435]I don't really want the Due because I'd like to be able to migrate the project to a barebones chip. Let's just say for example I wanted to use the Cortex-M0, like atmel's SAM20E. Can I program it through the arduino IDE and what programmer do I need to flash it?[/QUOTE] To my previous point, Energia supports the Tiva parts on the TI boards [url]http://energia.nu/[/url] . I wouldn't be surprised if MSP432 support was added at some point. Does the Arduino Due even have debugging? All ARM boards from the vendors that I've seen do which I'd say is a worthwhile investment.

[QUOTE=papkee;48099435]I don't really want the Due because I'd like to be able to migrate the project to a barebones chip. Let's just say for example I wanted to use the Cortex-M0, like atmel's SAM20E. Can I program it through the arduino IDE and what programmer do I need to flash it?[/QUOTE] Unless there's a specific arduino bootloader/firmware that works with the SAM20E, then you'll have to program it with the arm-gcc toolchain. Your best bet then is to use Atmel's pre-configured toolchain to program it (Begin the shaming for recommending to use any Atmel software). AFAIK, there isn't a standalone library/toolchain for Atmel ARMs compared to WinAVR.

[QUOTE=LoneWolf_Recon;48103654]Unless there's a specific arduino bootloader/firmware that works with the SAM20E, then you'll have to program it with the arm-gcc toolchain. Your best bet then is to use Atmel's pre-configured toolchain to program it (Begin the shaming for recommending to use any Atmel software). AFAIK, there isn't a standalone library/toolchain for Atmel ARMs compared to WinAVR.[/QUOTE] That's not that big of an issue. I just feel I'll miss muh arduino libraries. Although, I've heard that there's something similar for barebones programming. I dunno, maybe I will just use something like the 1284p. I always want to take the leap into straight C but every time I look at it I just get scared off.

Just made a 7 cell 18650 Li-Ion battery for my portables speakers. around 25Volts at 2.6Ah. I got some china BMS module for 7 cells, put all together into a box and drilled a hole in it, for an XLR Socket (3 V+, 2 Discharge, 1 Charge) Next thing is to get a Charger, maybe from an Ebike. They allready got XLR connectors, i just need to change the pinout. [URL=http://www.directupload.net/file/d/4036/3f88a2zy_jpg.htm][IMG]http://fs1.directupload.net/images/150702/temp/3f88a2zy.jpg[/IMG][/URL] [URL=http://www.directupload.net/file/d/4036/zgpu9n9u_jpg.htm][IMG]http://fs2.directupload.net/images/150702/temp/zgpu9n9u.jpg[/IMG][/URL] [URL=http://www.directupload.net/file/d/4036/7pc8zsuo_jpg.htm][IMG]http://fs1.directupload.net/images/150702/temp/7pc8zsuo.jpg[/IMG][/URL] [URL=http://www.directupload.net/file/d/4036/trd9ltv2_jpg.htm][IMG]http://fs2.directupload.net/images/150702/temp/trd9ltv2.jpg[/IMG][/URL] [URL=http://www.directupload.net/file/d/4036/8zq4k8j2_jpg.htm][IMG]http://fs2.directupload.net/images/150702/temp/8zq4k8j2.jpg[/IMG][/URL] [URL=http://www.directupload.net/file/d/4036/wjwl65fe_jpg.htm][IMG]http://fs1.directupload.net/images/150702/temp/wjwl65fe.jpg[/IMG][/URL]