I've used PCBExpress to design my first ever board (not quite accurate
- back in the sixties I played with copper clad boards and ferric chloride solutions, but the results weren't great.)
Before I spend money on having this commercially cut, I'm hoping someone will take pity on a relative newbie and point out any errors and stupidities in the board layout. I'm not asking for circuit analysis - just someone who has the time to look at how I laid the traces, and point up obvious problems. I've never done two layer before. It's been a lot of years since I did one layer.
Especially, there are a couple of points at which I have a component's leg going through the board, and a trace connecting to it on both the top and bottom layer. I'd like the top and bottom trace connected whether or not the component is installed, but PCBExpress wasn't totally clear on whether all holes for components are really cut as vias. It makes sense that they would be, but I'd rather not find out the hard way.
Anyway, it's all connectors, DIPs, resistors and caps, and hopefully not difficult for someone who does this for real to grok and comment on. Many thanks in advance. I promise to learn from my mistakes.
"ScottM" schreef in bericht news: snipped-for-privacy@u72g2000cwu.googlegroups.com...
Having a quick view, I saw no spectacular things. Some components/holes are pretty close to the edge but if ExpressPCB (not PCBExpress) does not complain why worry? Did you forget to draw mounting holes or do you have another method to fasten the pcb?
.gif (or png) is better for that kind of screen capture.
Best regards, Spehro Pefhany
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"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Red is top, green is bottom, board size is 3.8x2.5". Especially comment on what I'm letting myself in for in terms of soldering effort. It occurs to me that soldering points 0.1" apart is going to be difficult; is there a clever way to do this?
ExpressPCB did let me get the board laid out fairly quickly, and without solder mask and silkscreen I can get this done for $51. What's cheaper and better? I will need 2-3 custom boards, and if things go well, a number of copies of each down the road.
The power connections to the (obsolete) LM3900 appear to be reversed. You should probably have some bypass capacitors across the 5V & 12V supplies. I didn't attempt to understand all that you're doing-- but running CMOS input pins off the board directly is often not wise.
Checking hole sizes and noting clearances on each footprint/padstack is often not a waste of time.
No, just spend the 10 minutes and do it perfectly the first time, d*mmit.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
I'd alter the ~90deg bends to two ~45deg bends. See LM3900 pin 4 as an example.
Component pads will connect the top/bottom layers even without the component installed.
Since you are ordering MiniBoard's you won't get the silkscreen. I'd recommend lowering the text "Spot", "Exit", "Beep", etc to the top (red) layer. Ditto for any other text you'd find useful.
No, you'll find that's easy, we've all been doing it for more than 50 years. It's 0.05" that begins to show real issues, and 0.5mm (about 0.020") that raises your eyebrows. After that you can go for the really-miniature stuff.
- Use only 45deg angles (like the Exit & Beep tracks)
- I can't see why you need a double sided board for this, it could be done single sided with a few links at most.
- The pads are a bit small, make them bigger and oval shaped.
- You've put tracks on the top when you could have put them on the bottom. The top connector for example, the tracks should all be on the bottom, and only needed ones on the top.
Note these these are really just esthetics. Electrically I can't comment at a quick glance.
If you would include your .sch we could tweak it for you. Also this is such a simple board, you can do this yourself. save a bundle.. If you want to explore a simple method, go to teknics web site and order the press-n-peel blue toner transfer sheets. Makes it simple to make prototype simple boards. I believe on your board you have a gnd and supply tied together also on the right side of the board. Jtt...
I've posted a .bmp to www/obsessionaudio.com/dimmer2.bmp - I don't promise it's lovely. The .sch tool and I had some disagreements.
The idea is to get output from PWM generators (9 of them) and use them as follows:
3 are generating (varying) audio frequencies. I want to combine these (using XOR, for simplicity) into a single signal, bump up the voltage (ULN2003A), and put it across a small cap to grind off the square edges. Then it can go into a speaker or a small amp. I realise that XORing square waves doesn't exactly preserve the frequencies, but that's ok. I just need a rich source of different, simple sounds. (Usually, some or all all PWMs are turned off).
4 are generating output (probably at around 400kHz) for a commercial dimmer. I want to end up with 4 lines, each adjustable to 0 to +10v output, based on duty cycle. (The dimmer demands 4 lines varying between 0 to +10v and a common ground.)
I didn't know of a simpler way to boost the square wave from off/on to
0/+10v, so I'm using a norton op amp with a 12v input, and then a voltage divider to get the output down to 0-10v, and then a cap to smooth out the waveform. I have something like this running on a breadboard and it works reasonably well. But I don't like using an op amp for this, because it means extra resistors, to pull up the (-) leg. And the part is apparently obsolete now. Can I safely use some simpler device for this? What's the right way?
2 are generating output for an array of LEDs, which I want to "dim by brute force". But since the LEDs are common anode, I can use a ULN2003 to amplify the square wave, and just put it through a resistor and across a cap to get a little smoothing and current control.
All the PWM is coming off a PC104 card and the available current is typically 2ma on each output pin. I worry about drawing too much current and blowing a $200 card. I also worry about radiating noise by sending a 400kHz square wave over a ribbon cable. And I wonder if (as someone mentioned) bringing signals over from another board is just going to create a lot of noise problems.
So, some questions:
1) Is there a better way to do this. My design skills... well, I'm a software guy. My code looks gorgeous. I doubt those circuits look as good.
2) Several people have recommended avoiding right angles in traces. Because they fail? Because they are ugly? Because electrons don't corner well?
I've noted the advice about going single layer, and I'm thinking about it. I don't want to do my own boards though - I don't have a drill press and I really do want to mount through holes, given my soldering skills. Speaking of which, what's a good soldering iron? My "radio Shack special" has too blunt a tip to get into 0.1" places, and the fancy "Cold heat" portable I got is a pain to use.
OK, the LM3900 looks like a bad idea. Would this work instead?
TC4468:
formatting link
All I want to do is take the output of a PWM (which has very little current available) and raise it up to 0-12v; it looks like this chip will handle up to 16V, and from the looks of things, only draws 10uA, so connecting it directly to a source-2ma-at-most pin ought to be very safe, yes?
Looks good, except I'd double the power and ground traces - put +V on the top, and put them opposite each other, and go all the way around the perimeter of the board, plus - well, heck - just fill up the whole rest of the top of the board with ground plane. (wherever there isn't circuitry, of course! ;-) )
Assuming it's still just data, that shouldn't take long at all.
Hand-soldering larger SMD parts is *easy*. In fact, somewhat easier than through-hole parts. To solder an 0805 resistor, for example:
Pre-tin one of the pads with a little solder.
Put 0805 part in the right place over the pads, hold down with something pointy (I use pointy tweezers, you could use a toothpick).
Touch the pre-tinned pad to melt the solder. Make sure you're pushing down (lightly) on the part at this point; it will settle onto the pad as soon as the solder melts, but it's really easy to move it around with the surface tension of the solder at this point. Pressing down on it makes it stay in place.
Solder the other pad.
You can use this technique for parts with a small number of pins. For larger parts (SOJ or QFP), you tack down opposite corners using the pre-tin method, then drag a blob of solder across the pins to solder them all down quickly. A little desoldering braid cleans up any shorts, if any.
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