Electrical Engineering V2 - Developers

[QUOTE=Guzbone;41869767] So if I get something like [URL]http://www.adafruit.com/products/1065[/URL] then you just put it between the battery and the raspPi on the positive line? Also I've looked into the whole splicing on a usb plug and it seems quite easy, I have this issue where I always imagine things to do with electrical engineering to be more difficult than they really are and seemingly impossible. Need to remember you can jerry rig anything just about. [/QUOTE] Yes, just pop that between the two and you're good to go. On the more difficult side of things, say if you designed a dc-dc converter from scratch. Its hard initially, but most of the math for standard analog electronics comes to you in time (Most of it involves integration, differentiation, etc). Just remember to reverse engineer everything and you'll be one step ahead of some of the math. [URL="http://www.mouser.com/ProductDetail/RECOM-Power/R-78B50-10/?qs=sGAEpiMZZMtwaiKVUtQsNS6SOjapLQbCEo2CpGKm1MM%3d"]Here's something cheaper and equivalent[/URL]

Have it output 3.3V and directly hook it up to the 3.3V bus to save some more power, as the Pi has a 3.3V linear regulator on board.

[QUOTE=chipset;41869900]I would advise against buying from adafruit, sparkfun, makershed, radioshack or any other sites aimed at makers as they are generally extremely overpriced. That dc-dc converter module you linked probably costs adafruit $0.5 a piece from the supplier. Try more professional sites like digikey, farnell, mouser etc. They are all great but shipping might be expensive (you'll have to check it out, not sure) and their sites are enormous and challenging to navigate but the parts are dirt cheap as they generally deal in quantities of thousands. For small orders I buy my components from [URL="http://www.bitsbox.co.uk"]www.bitsbox.co.uk[/URL] but they don't ship to north america, I'm pretty sure you can order from farnell.com with free shipping in the USA, not sure about canada. As I'm european I can't really help you much with retailers but ebay is always an option. Loads of chinese sellers have free shipping and dirt cheap parts, but they are sometimes counterfeit parts. See if you can find any canadian or american ebay electronics sellers. Oh, and check these out: [URL]http://www.ebay.ca/itm/DC-DC-Boost-Buck-Converter-Step-Up-Step-Down-Supply-Module-3-35V-to-2-2-30V-S5-/251316934129?pt=LH_DefaultDomain_0&hash=item3a83a815f1&_uhb=1[/URL] Dirt cheap dc-dc buck boost modules, all you have to do is hook up the batteries at one end, twiddle the potentiometer to get 5 volts out and connect the pi in the other end. They're from china though so expect 3-4 weeks shipping time.[/QUOTE] That DC-DC board from eBay is garbage. I ordered a few (Step up/down) and they get burning hot and the voltage drops way down with a tiny load. Notice they do not list the efficiency... I'd estimate it's somewhere between bugger and fuck all, although TI list it as 80% typical I doubt they're real TI parts, or something else is wrong. Edit: In fact, the ones I bought came with a little spec sheet listing the full load temperature rise as 45c, but with the 4 that I ordered at 12.6v (3s LiPo) in, 5v out with a 50mA CC load they were burning hot. They might work with a heat sink but otherwise no good. Edit edit: Also, that part from Adafruit is $10 in singles from Newark [URL]http://www.newark.com/tracopower/tsr-1-2450/dc-dc-conv-non-iso-pol-1-o-p-1a/dp/08R5932[/URL]

[url]http://www.digikey.ca/product-detail/en/V7805-1000/102-1715-ND/1828608[/url] Probably go with this or something similar, trying to keep my orders as large as possible as I'd rather not order parts from a dozen different companies, very likely I'll get any circuitry stuff from Digi-key, including as circuit board since I figure I'll want to do a more permanent mount for this stuff than a bread board.

[QUOTE=Xera;41872104]That DC-DC board from eBay is garbage. I ordered a few (Step up/down) and they get burning hot and the voltage drops way down with a tiny load. Notice they do not list the efficiency... I'd estimate it's somewhere between bugger and fuck all, although TI list it as 80% typical I doubt they're real TI parts, or something else is wrong. Edit: In fact, the ones I bought came with a little spec sheet listing the full load temperature rise as 45c, but with the 4 that I ordered at 12.6v (3s LiPo) in, 5v out with a 50mA CC load they were burning hot. They might work with a heat sink but otherwise no good. Edit edit: Also, that part from Adafruit is $10 in singles from Newark [URL]http://www.newark.com/tracopower/tsr-1-2450/dc-dc-conv-non-iso-pol-1-o-p-1a/dp/08R5932[/URL][/QUOTE] I haven't done any extensive testing with these but I never noticed them getting especially hot so I'm gonna have to test your claims before I trust you on that. And yes, 50 cents was an exaggeration and I didn't bother to look up a price, but my point still stands. Edit: I don't know which dc-dc modules you've been dealing with but I just left mine for about 5 minutes (exactly like the one I linked to on ebay) stepping down 12v to 5v and loading the output at 1A and my IR thermometer says it's not gone over 50C yet. The output rectifier diode does feel a tiny bit hotter than the main device but it's not burning my finger so it's definitely below ~55C. Edit: I also just configured it for a more realistic use, outputting 33 volts at 400mA which is slightly above what it takes to power a 10W LED. I also put a box over it so that it would not get any airflow. A few minutes later, temperatures where not increasing noticeably and the main device was at 80C. Perfectly acceptable but even a small heatsink and any amount of airflow would put it on the comfortable side of 70C.

[QUOTE=chipset;41879063]I haven't done any extensive testing with these but I never noticed them getting especially hot so I'm gonna have to test your claims before I trust you on that. And yes, 50 cents was an exaggeration and I didn't bother to look up a price, but my point still stands. Edit: I don't know which dc-dc modules you've been dealing with but I just left mine for about 5 minutes (exactly like the one I linked to on ebay) stepping down 12v to 5v and loading the output at 1A and my IR thermometer says it's not gone over 50C yet. The output rectifier diode does feel a tiny bit hotter than the main device but it's not burning my finger so it's definitely below ~55C. Edit: I also just configured it for a more realistic use, outputting 33 volts at 400mA which is slightly above what it takes to power a 10W LED. I also put a box over it so that it would not get any airflow. A few minutes later, temperatures where not increasing noticeably and the main device was at 80C. Perfectly acceptable but even a small heatsink and any amount of airflow would put it on the comfortable side of 70C.[/QUOTE] Hmm, guess I got a bad set then. I didn't buy from that seller but they look identical and use the same TI part.

Hey guys, I'm starting my Mechatronic Engineering course at uni in a few weeks, was wondering if you guys had any reading you'd recommend before I start my course? I'm fairly confident with simple electronics, but some of the more complicated concepts still baffle me. Any help would be appreciated :)

[QUOTE=Falcqn;41884509]Hey guys, I'm starting my Mechatronic Engineering course at uni in a few weeks, was wondering if you guys had any reading you'd recommend before I start my course? I'm fairly confident with simple electronics, but some of the more complicated concepts still baffle me. Any help would be appreciated :)[/QUOTE] Art of Electronics is perhaps the best book to read, but before or along with that you should make sure you know at least some of the following stuff and the rest you can learn as you go along, I probably should point out that some of the stuff is very complicated and you would not be expected to learn it, although a basic understanding is helpful. [quote] Ohm's Law Joule's Law (power) Voltage & current divider resistive circuits Non-ideal component effects (tolerance, temperature coefficient, etc) Simplification of series, parallel and mixed circuits. Thévenin's and Norton's theorem. Analysis by superposition Maximum power transfer theorem Capacitive and inductive time constants, RC and RL circuits. AC sources and harmonics AC phase AC reactance and impedance Resonance and tuned LCR circuits Digital circuits, logic gates, flip-flops, latches, timers, counters, etc Transistors, bipolar, jfet, mosfet and igbt. Thyristors, SCR, DIAC, TRIAC, UJT, etc Positive and negative feedback Operational amplifiers, phase margin, etc Oscillators and filters Bandwidth and Q factor Component parasitic effects on RF signals etc etc etc. [/quote]

Art of electronics is amazing. It'd be great to read up on the stuff Chryseus listed, but don't worry if you find it a bit daunting - a lot (if not most) of that will probably be covered in the first year of the course anyway. Even Ohm's law will probably be flashed about on a slide or two in the first couple of lectures :smile:

Finally managed to control the LED Driver. It has a very tight timing requirement for a bitframe, which is between 0.33 µs and 10µs. As my AVR is only running on 16 MHz, I at first couldn't even reach the 10 µS mark, as the execution of the code took way too long, so I had to optimize it from 30µs down to 9µs. [img]http://i.imgur.com/qc0bfwG.jpg[/img]

Did you use a timer interrupt routine? What is the LED driver?

[QUOTE=LoneWolf_Recon;41892843]Did you use a timer interrupt routine? What is the LED driver?[/QUOTE] No, I just used delays. This is the driver: [url]http://www.ti.com/product/tlc5973[/url]

[QUOTE=Chryseus;41885503]Art of Electronics is perhaps the best book to read, but before or along with that you should make sure you know at least some of the following stuff and the rest you can learn as you go along, I probably should point out that some of the stuff is very complicated and you would not be expected to learn it, although a basic understanding is helpful.[/QUOTE] Yeah, I'm pretty comfortable with a decent amount of that list; we covered most of that in A-Level Electronics/Physics. Art of Electronics looks really comprehensive, cheers guys!

:dance: Got sound out of my 1949 Cossor 494AC, I expected a lot more effort required but I only needed to replace the main filter electrolytic, of course I need to replace the rest of the capacitors or they might decide to leak or explode.

[QUOTE=Falcqn;41884509]Hey guys, I'm starting my Mechatronic Engineering course at uni in a few weeks, was wondering if you guys had any reading you'd recommend before I start my course? I'm fairly confident with simple electronics, but some of the more complicated concepts still baffle me. Any help would be appreciated :)[/QUOTE] well shit, I'm about to start mechatronics as well in a week or 2.

I'm messing around with an idea for work. We're working on the new 911 call center and the dispatchers and finding that using CTRL-CTRL-1-Enter and CTRL-CTRL-2-Enter is too time consuming to switch their keyboard and mouse between machines. We're looking at fancy USB switches that cost around $450, though the USB switching time on the KVMs we have installed is already pretty quick. It's just the key combo that's slow. I had an idea, which was to use a microcontroller like a Teensy to do the shortcut to toggle between the machines. Then stick it in a little box or a Staples easy button. If it works and both our boss and the dispatchers approve it, I could possibly have something of mine being used multiple times per day in the 911 call center after I leave.

I'm very excited for it, but I have no clue as to how difficult it is going to be. In 3 to 4 days I'll get my first timetable and see how shit goes down at my new school in the week after.

I need to etch a few boards. [t]http://i11.photobucket.com/albums/a166/ballsandy/Computer%20related/MC6800.png[/t] Everyone's so expensive though.

[QUOTE=pentium;41944782]I need to etch a few boards. [t]http://i11.photobucket.com/albums/a166/ballsandy/Computer%20related/MC6800.png[/t] Everyone's so expensive though.[/QUOTE] Custom PCI or ISA card? What'll coprocess?

[QUOTE=pentium;41944782]I need to etch a few boards. [t]http://i11.photobucket.com/albums/a166/ballsandy/Computer%20related/MC6800.png[/t] Everyone's so expensive though.[/QUOTE] What CAD did you use?

[QUOTE=DrDevil;41948020]What CAD did you use?[/QUOTE] I had to use GIMP because I literally copied it from a 20 year old german magazine article and had no dimensions or immediate accuracy of scale. It's the nasty way to do it. It's a card for an Apple II that gives you the 8-bit variant of the MC68000. You can write hybrid 6502 and 68K code that can have the two CPU's running at the same time.

[QUOTE=pentium;41948427]I had to use GIMP because I literally copied it from a 20 year old german magazine article and had no dimensions or immediate accuracy of scale. It's the nasty way to do it. It's a card for an Apple II that gives you the 8-bit variant of the MC68000. You can write hybrid 6502 and 68K code that can have the two CPU's running at the same time.[/QUOTE] I feel really sorry for you

[QUOTE=pentium;41948427]I had to use GIMP because I literally copied it from a 20 year old german magazine article and had no dimensions or immediate accuracy of scale. It's the nasty way to do it. It's a card for an Apple II that gives you the 8-bit variant of the MC68000. You can write hybrid 6502 and 68K code that can have the two CPU's running at the same time.[/QUOTE] [t]http://i.imgur.com/JTqefuo.png[/t] This bit is never going to etch well :( (unless you drew it at a higher res and this is just a scaled down version) Most CADs will have some way of importing bitmaps and you could then have drawn the traces over the top? And it's going to be expensive to get a single board fabbed! Do you have any experience etching at home?

Different people have their methods but I'd laser print that onto some magazine paper and do the toner transfer method, drilling some holes after doing one side so you can locate the other. I'd then beef up some of the dodgy traces with an etch resist pen. Especially those ones r0b0tsquid pointed out. If you need affordable PCBs, [url=http://www.seeedstudio.com/depot/fusion-pcb-service-2-layers-p-835.html]Seeed[/url] are cheap as chips (heh) but the lead time is loooooong. And you'll need to remake the design in a CAD program they support.

[QUOTE=Tezzanator92;41951977] And you'll need to remake the design in a CAD program they support.[/QUOTE] Not quite, every CAD outputs gerber files, which are the same for every cad.

I meant more from the point of view that uploading a PNG file and expecting to get a PCB back isn't going to work (in direct reference to the scan above). But you are correct any CAD that can output gerber files will work. Seeed are a little strict on the settings you use though, I've had designs rejected for export settings being off. Understandably so, as they are doing them for pennies. Just had a look on their site, it's been a while... They do fully assembled boards now too o.0

[QUOTE=r0b0tsquid;41951236][t]http://i.imgur.com/JTqefuo.png[/t] This bit is never going to etch well :( (unless you drew it at a higher res and this is just a scaled down version) Most CADs will have some way of importing bitmaps and you could then have drawn the traces over the top? And it's going to be expensive to get a single board fabbed! Do you have any experience etching at home?[/QUOTE] That's Photobucket. Even though it was uploaded as a PNG they add compression which blurs the lines. I ran a test on a transparency sheet and the spacing isn't so tight. I planned on having at least a dozen boards made because I can sell the boards off to those who also want to build the kit.

I need to get into etching my own boards, too. Working at this job I get access to all sorts of old thermostats and furnace boards, nearly all of which contain a microcontroller of some kind. And apparantley you can program them even if they're bit-locked, you just can't read what's written on there. (for the ATMegas anyway)

[QUOTE=pentium;41952445]That's Photobucket. Even though it was uploaded as a PNG they add compression which blurs the lines. I ran a test on a transparency sheet and the spacing isn't so tight. I planned on having at least a dozen boards made because I can sell the boards off to those who also want to build the kit.[/QUOTE] It was the aliasing more than the blurriness that I was referring to, but okay! To my knowledge though gerbers are a vector format? (if you're planning on the professional route for larger volumes) Also, vias are great fun if you're etching at home...

So I started poking around on the old thermostat I got from work (formerly Carrier's top-of-the-line thermostat) and am puzzled about a component on it. I'm pretty sure it's the temperature/humidity sensor, but the markings on it don't yield any results via Google. It reads "B5N 11" on the part itself, and the mini-PCB that part is mounted to (which is then mounted to the main PCB) reads "SHT". But on a positive note, this thing also has a pretty spiffy looking microcontroller in it, though programming it would likely be beyond my capabilities, as the manual I found online for it is 935 pages long. :v: It also has one of these little guys on it. Could be useful, but somehow seems like over-kill for a thermostat. [url]http://pdf1.alldatasheet.com/datasheet-pdf/view/173432/MAXIM/MAX3443ECSA.html[/url]