Electrical Engineering V2 - Developers

[QUOTE=alexaz;44297063][img]http://i.imgur.com/yS2uSZl.png[/img] Well, shit... Didn't think 20QFN is that small.[/QUOTE] Ugh, i did the same thing a while ago with some SMD chips.... When i need them, i will likely glue them upside down and wire them just like they bond the tiny semiconductor wafers inside them

Get an adapter board, a hot air gun and flux. Tin the pads with a soldering iron, apply ample flux. Preheat the board, then place the qfn IC on the footprint, it should just snap into place on it's own.

Why. [url]http://www.bad-dog-designs.co.uk/testclocks.html[/url]

[QUOTE=nuttyboffin;44285616]As it happens. no, this is because all capacitors have reactance. each AC signal will be affected differently by the capacitors. Xc = 1/(2*pi*F*C) Xc is similer to resistance, but for AC and it only means anything to the Frequency it reacts to.[/QUOTE] [t]http://www.tutapoint.com/kcimages/EquivalentImpedanceJasonL.jpg[/t] You can add them up...

[QUOTE=ddrl46;44324522]Why. [url]http://www.bad-dog-designs.co.uk/testclocks.html[/url][/QUOTE] [quote]This started out as a little resistance decade test box circa [U]1930[/U]. Built like a tank and the moment I saw it I knew it would make a superb little steampunk clock. Quite a bit of work, [U]remove all the insides[/U], and then [U]drill / resize everything[/U] to accommodate 4 GN-4 Nixie tubes along with 2 Colon indicators between the Hours and Minutes.[/quote] Wow. I think we can be glad that the end results on this page are at least not utterly terrible. [URL="http://www.bad-dog-designs.co.uk/captain_nemo.html"]That former 1890s music box though...[/URL]

[QUOTE=Tamschi;44325763]Wow. I think we can be glad that the end results on this page are at least not utterly terrible. [URL="http://www.bad-dog-designs.co.uk/captain_nemo.html"]That former 1890s music box though...[/URL][/QUOTE] [quote]steampunk clock[/quote] [media]http://www.youtube.com/watch?v=TFCuE5rHbPA[/media] 2:16

[QUOTE=Zero-Point;44325883][media]http://www.youtube.com/watch?v=TFCuE5rHbPA[/media] 2:16[/QUOTE] Oh god... that is brilliant...

[QUOTE=nuttyboffin;44328221]Oh god... that is brilliant...[/QUOTE] If you like that one, check out "Sir Reginald's Marvelous Organ". :v:

What is the best way to simulate coils in 3D space? I want to simulate air space transformer on around 27Mhz (obviously slowed down). I want to see/make happen electric flow, magnetic flux and magnetic induction from another coil (and vice versa). Is it possible? (anyone knows any software or hint)

[QUOTE=HeatPipe;44332530]What is the best way to simulate coils in 3D space? I want to simulate air space transformer on around 27Mhz (obviously slowed down). I want to see/make happen electric flow, magnetic flux and magnetic induction from another coil (and vice versa). Is it possible? (anyone knows any software or hint)[/QUOTE] If somthing like this exists, the person who coded it can have all my money.

[QUOTE=HeatPipe;44332530]What is the best way to simulate coils in 3D space? I want to simulate air space transformer on around 27Mhz (obviously slowed down). I want to see/make happen electric flow, magnetic flux and magnetic induction from another coil (and vice versa). Is it possible? (anyone knows any software or hint)[/QUOTE] You can fairly well approximate a gapped core, a gap increases the core reluctance which in turn lowers the inductance per turn (A_L) [Gap reluctance] R_g = l_g / (μ_o * A_e ) [Core reluctance] R_c = l_e / (μ_o * μ_r * A_e) [Total reluctance] R_L = R_g + R_c Where: l_g = gap length μ_o = permeability of free space A_e = Core area l_e = Effective length μ_r = Relative permeability The air gap also stores energy [b]much[/b] more effectively than the ferrite core by itself and allows you to achieve a higher magnetic flux before saturation occurs at the cost of more turns being needed to provide the same inductance which makes it very useful for energy storage inductors and flyback transformers. For an accurate model that takes a bit more effort, some advanced (read: expensive) software includes models for non-linear inductors and magnetic cores, but generally I would recommend experimentation over trying to model it. [url]http://www.edacafe.com/books/PSpice/san63267_ch02.pdf[/url]

I have a question about feedback if anyone knows... [IMG]http://i.imgur.com/3d2mxZx.png[/IMG] I believe this is an example of voltage-shunt feedback. I've been told the gain of the feedback stage, B, is 1/R_b, where B = v_feedback over v_out. My problem is I can't figure out how they came to 1/R_b. I've tried a few things and keep getting it wrong...

[QUOTE=No_Excuses;44346590]I have a question about feedback if anyone knows... [IMG]http://i.imgur.com/3d2mxZx.png[/IMG] I believe this is an example of voltage-shunt feedback. I've been told the gain of the feedback stage, B, is 1/R_b, where B = v_feedback over v_out. My problem is I can't figure out how they came to 1/R_b. I've tried a few things and keep getting it wrong...[/QUOTE] I think the easiest way to calculate those is if you want a specific current to flow through R_c, which will be I_C + I_B, although you can usually ignore I_B as that current is relatively small. Now that you know the current, you can do I_C/Beta and thus get I_B. Now calculate the voltage across R_b with Vcc - R_c - 0.7V, and you have your resistor R_b.

[qUOTE=DrDevil;44346914]I think the easiest way to calculate those is if you want a specific current to flow through R_c, which will be I_C + I_B, although you can usually ignore I_B as that current is relatively small. Now that you know the current, you can do I_C/Beta and thus get I_B. Now calculate the voltage across R_b with Vcc - R_c - 0.7V, and you have your resistor R_b.[/QUOTE] I ignored the I_B like you said...but I don't quite follow the last part though. Sorry, I'm having lots of troubles with this. Well heres my thoughts anyways. If B=v_f / v_o... V_f = ??? v_o = Vcc - Ic Rc = 0.7V + Ib Rb

Yeah electrical engineering is pretty hard.

[QUOTE=No_Excuses;44346590]I have a question about feedback if anyone knows... [IMG]http://i.imgur.com/3d2mxZx.png[/IMG] I believe this is an example of voltage-shunt feedback. I've been told the gain of the feedback stage, B, is 1/R_b, where B = v_feedback over v_out. My problem is I can't figure out how they came to 1/R_b. I've tried a few things and keep getting it wrong...[/QUOTE] Let us assume some initial values: Vcc = 10V βF = 100 Iq = 1mA Vq = 5V Since both the base and collector current flows through Rc the voltage dropped across it is proportional to (Ic + Ib) * Rc Ignoring the base current (which usually is small enough to have no real impact) we can work out the collector resistor we need given the desired quiescent voltage of 5V and quiescent current of 1mA. 5V / 1mA = 5k From there we can work out the required base current given the βF of 100 Ib = 1mA / 100 = 10uA. Knowing that the base resistor can be calculated as (5V - 0.6V) / 10uA = 440k. All being well this should give a collector DC voltage of 5V. As a result of this any change in βF will results in a inverse change in collector voltage which will reduce the base current which helps prevent thermal runaway. The gain of the circuit is Rc / Re, which in this case Re is the intrinsic emitter resistance, also referred to as the transconductance gm, this is calculated as Ic / Vt, Vt is the thermal voltage which is most cases you can consider to be 25mV, thus giving Re = 0.04 Ohm. The resulting gain is then 5k / 0.04 = 125000 In practice I can't recommend this circuit at all, it often requires manual tweaking to get the output voltage correct and the input impedance is very poor being βF * Re (4 Ohm) and the gain shifts a lot with Ic giving a rather non-linear output, it can be improved by adding an emitter resistor, which actually performs the same functions protecting against thermal runaway. At the bare minimum I'd add a resistor to drop at least 1V across the emitter, 1V / 1mA = 1k

Thanks for the practice. It probably doesn't seem like it but I know all that. I edited my previous post as you were posting that which should show what specifically I'm stuck with. And yeah its not a bias scheme I would use but I still want to know how to derive the feedback gain for the sake of completeness. I can do it for other bias schemes fine, just not this one and its bugging me.

The gain comes from the following: [php] -β * Rc Rc B = ----------- which is approximately the same as ------ (β+1) * Re Re[/php] I'm not exactly sure how 1 / Rb works either but it seems to give a value I would expect.

[QUOTE=Chryseus;44350332]The gain comes from the following: [php] -β * Rc Rc B = ----------- which is approximately the same as ------ (β+1) * Re Re[/php] I'm not exactly sure how 1 / Rb works either but it seems to give a value I would expect.[/QUOTE] Your approximation makes no sense as the B you calculated must be negative.

Have you guys got experience with ordering stuff from Farnell? I just ordered some stuff way under the 50 euro minimum they ask from non-corporation customers, and I got a mail from them with the same line but the order has not (yet) been cancelled. Wil they not deliver or make an exception for your first order (which I think is highly unlikely)

[QUOTE=DrDevil;44350543]Your approximation makes no sense as the B you calculated must be negative.[/QUOTE] My bad, that negative should not be there. [QUOTE=scratch (nl);44351675]Have you guys got experience with ordering stuff from Farnell? I just ordered some stuff way under the 50 euro minimum they ask from non-corporation customers, and I got a mail from them with the same line but the order has not (yet) been cancelled. Wil they not deliver or make an exception for your first order (which I think is highly unlikely)[/QUOTE] It very much depends on what country you're in.

[QUOTE=scratch (nl);44351675]Have you guys got experience with ordering stuff from Farnell? I just ordered some stuff way under the 50 euro minimum they ask from non-corporation customers, and I got a mail from them with the same line but the order has not (yet) been cancelled. Wil they not deliver or make an exception for your first order (which I think is highly unlikely)[/QUOTE] They'll probably cancel it. Did you order through their site or send them an email like they ask you to?

[img]http://www.ti.com/ww/en/analog/Amplifiers-eBook/images/BREAD_BAKE_new.jpg[/img] Have some reading material. [url]http://www.ti.com/ww/en/analog/Amplifiers-eBook/[/url]

Jesus christ that title image

[QUOTE=DrDevil;44360173]Jesus christ that title image[/QUOTE] I know right who puts frosting on an apple turnover. Ridiculous.

Still doesn't beat Teach Yourself: [IMG]http://ecx.images-amazon.com/images/I/51H27RD36ML._BO2,204,203,200_PIsitb-sticker-arrow-click,TopRight,35,-76_AA300_SH20_OU02_.jpg[/IMG]

[img]http://images.betterworldbooks.com/007/Teach-Yourself-Electricity-and-Electronics-Gibilisco-Stan-9780071459334.jpg[/img][t]http://www.standardsmedia.com/book_images/7039_9780071741354.jpg[/t][img]http://mheasiast.files.wordpress.com/2010/05/electricity-experiments-you-can-do-at-home-9780071621649.jpg[/img] What is this... I'm hungry for some electronics.

What the hell, is this some kind of fetish?

i'd take a byte out of that if you know what i mean

[QUOTE=Leestons;43959275]Please make a video when it's done. Sounds great.[/QUOTE] I forgot to make a video, but here's a pic of the final [del]clusterfuck[/del] breadboard prototype. At the moment I'm working on a prototype board, which is almost done as well. [t]https://dl.dropboxusercontent.com/u/43645231/photos/electro/crane.png[/t] the 3 rotary encoders are to prevent the crane from driving past it's limits. As far as I know the programming side of things is all done now.