Thanks for the feedback - I also have access to powerpcb - is that much better?
There are two things I need in a pcb design package - easy ability to create custom decals/footprints as I am using some very specific parts and secondly I need to overlay a CAD drawing of the board as I need to be VERY specific in the layout of the components. Its a double sided board so two cad drawings would be perfect.
Products like Eagle just don't suppor this sort of thing (that I've foudn so far)
I was actually assuming a standard VGA output when I wrote that. With other forms of analog video (e.g., a composite NTSC output, S-Video, etc.) the task is somewhat worse, due to the need to decode the video into RGB in addition to the tasks previously mentioned.
Eagle will let you do most of that out of the box (so to speak). It does do custom footprints (and various silkscreen layers). I found it easy to create a new package. Weakness on new package layouts, circular holes only for through hole (If you need a slot you have to build it up). There are probably other weakness but for straightforward double sided boards I doubt you will notice.
As far as CAD overlay. There is support in Eagle to allow it but how easy it is to do I don't know. Check out the DXF importing utilities on their website (they also have support newsgroups). I think it should be possible to import a dxf into an unused layer and use that as a guide, but I haven't done it. Ask in their support newsgroups someone may have done it.
Again check for DXF import utilities on Cadsofts support area. There is/are some image import utility/ies as well but I didn't much care for the result lasr time I tried.
I've not had a problem with placing on as fine a grid as is unreasonable. (and in fact you can also position using absolute coordinates from the keyboard, very useful when trying to match existing mechanicals)
I also need the silkscreen layer but that's separate. I was referring to the outline layer. The problem is most entry level progs don't let you import files for the layers.
Other progs don't let you specify the location of the components precisely outside of the 2.54mm grid.
I'm using this circuit to control a short (1s) pulse of 14A through an electromagnet coil. The coil is 3 separate windings of 3 ohms each, which should give about 13.5-14A when switched on. I'm putting in a protection diode to stop the inductor destroying the mosfet when it's switched off. The question is, how do i work out the current rating for the diode and the wiring to it? I'm using heavy 30A wire for the wires between the battery, magnet, and mosfet, wired through an electrician's terminal block, but i'm not sure if i need to do the same with the diode.
P.S. the way i'm thinking of constructing this is to put the BUZ10 in a piece of stripboard, with all the terminals soldered just to hold it in place, but leave the ends of the terminals sticking out so i can solder the high current wire directly to them. I.e. the gate is using the tracks on the board, but the source and drain are soldered directly to the cable. Is this a good way to do it?
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Remember how RS used to ask for your name and address for even the smallest purchase? A friend of mine was buying a small part and the salesman asked the usual and my friend refused. The salesman was persistent so after being asked several times my friend relented said his first name was "YO". The salesman wrote that down and then my friend said his last name was "MAMA". The salesman finally took his money. ERS
no. The time just needs to be just long enough for the coil to reach its peak (resistance determined) current, so as not to waste power keeping it alive longer than needed.
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Would decreasing the resistor to 1k or 200ohm be enough? The transistor is being driven from the inverting output of a CMOS monostable.
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The switch won't be slow to turn off. The current through the inductor will be slow to reach zero, since it will free wheel through the diode. The time constant of the current decay is roughly L/R of the inductor. If you put a resistor in series with the diode, you allow more peak reverse voltage to develop (the peak inductor current times the resistance) but the decay time constant then becomes L/(Rind+Rseries). And the resistor also has to handle the peak current. Other voltage drop elements can also be used, like several diodes in series, or a big zener in series with the diode. If a slow release of the magnetic field is no problem, then just use one diode.
A follower is an amplifier that provides current gain, but has a voltage gain of very nearly one. Power varies. This one is an integrated transistor operated as an emitter follower (that also includes short circuit current limit and over temperature cut off) with the LM317 acting as a constant current load (1.2 volts at its output loaded with a resistor so that it passes 1.2/r through the resistor, and only a tiny bit more than that at its input. So the pull down current is limited to this fixed current, and the pull up current is limited by the higher current limit of the integrated transistor. Just a beefy but protected emitter follower.
Here comes the run on sentence of the month, courtesy Active8 :)
Because that way, when you go to Radio Shack and ask for a wall wart and the sales puke doesn't know WTF you're talking about, and you show him, he'll insist it's whatever *they* call it, and then you'll know what you're dealing with at RS.
Then you go to the computers and type in one of their names as the password to log on, and change the password >:)
What you are looking for is any package that imports DXF's (or DWG's). Do mechanical in mechanical, electriconic in electronic.
Import you board outline, slots, and other sundry non electronic component pcb holes etc.,from a mech. cad package (Autocad or a clone) as one layer. Do your 'tronic work on other layers - however many you need.
Lots of cad packages do this. They are not expensive. See Terry Pinnells website for a mega list of 'tronic cad and download some demo's. EasyPC will do all you need here for about $160 but there are loads more. Do not spend a fortune on an 'all singing all dancing' package if you are not going to use it regularly - you will spend hours, days, weeks, every time just trying to figure out how to do something in some of the more complex packages such as Cadstar, Pads etc. If you use them very regularly they are good otherwise they are worse than hopeless.
Hi, You already got your answers but I would like to add: The fuse that you describe is probably expecting AC. You would be better off with an automotive fuse, they are usually rated 32VDC. There is a slight difference in performance, probably not of any concern to you now but I mention it just for you education since your previous posts indicate to me that you want to learn. Best Regards, Tom
I was also thinking that the Vgs(th) was a loose spec and (I'm talkin parallel RC on the gate to ground/source here - forget that drain - gate cap) that even though the gate voltage is dropping slowly, the mosfet is being a sensitive prick. They're nice that way and it's a useful feature. They are used as on/off switches more often than not.
So your thought to try a bipolar tranny might just be the ticket but then you'd have to deal with the RC net discharging though the base. Bummer, eh? A Darlington pair migh help a bit. I'd also use a resistor in series with the gate so that the cap discharges into the
595 and skip the diode.
The prob I see with either case is the exponential charge/discharge nature of the RC net. If RC is the time constsnt, that's the time it takes for a cap to charge to 63%, IIRC of the charging voltage or discharge to 37% of it's initial charge. Then for the next RC interval, it only changes that same percentage of what's remaining. It's not a linear thing so the control voltage of your switching active is probably going to rapidly shoot right past that point where the active is in its linear region.
I'd probably forget this RC approach. It's subject to mfg process variations and everything else.
There are capacitor switches that charge one cap with the supply, then connect it in series with the supply to double it. These need only a couple capacitors to double (or make a negative of) a supply. The base number for one such chip is 7660.
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