Yeah, I thought about that! I've never home etched a complex double sided board before, what do you think is the smallest hole most people can reliably drill at home with a cheap drill press?
I know this will sound big and ugly, but make the hole at least 12mil, the outer diameter 30mil. The reason for the huge size is that when exposing home made boards, the top and bottom layer aren't always perfectly aligned and also when drilling though, a slight error in alignment can push off the copper pad on the other side if it is too thin.
The smallest I would go would be 10mil drill with 26 mil outer diameter, but, the above measurements would be better.
Careful with your transistor & passive component library, make sure they don't have smaller holes than what I've listed above.
For transistors, make sure the TO-92 has a the wide off-center center pin footprint spacing. Since we might need to solder on the top and bottom, if the center pin is pushed back, soldering on the top of the PCB is much easier to do without shorting to the 2 adjacent pins. Everything else should be easy to solder on both sides.
For the traces, I would mostly route 12mil, saving 10 mil when going under 1206 smd caps and resistors & sot23.
Thanks! Once I get back to my computer tonight I'll grab those. That'll make it a lot easier to convert. I can also send you the DipTrace schematics in PDF form if you don't want to download DipTrace. (I've got Ghostscript setup as a PDF printer.)
My intent was just to share it with the forum community. I figure once the boards are done, I'd see how many other people want them, order a batch and then order enough parts to do them all. The parts will obviously be a lot cheaper if ordered in larger quantities. (If just five people are interested in kits the price can be almost cut in half!)
I'm doing this because I think it's an awesome project and I want one myself! It's also a bit of a challenge to do layout for. I'm not looking to commercialize it or to make any money off it; any parts kits would be sold to forum members at cost.
I did plan on releasing the Gerbers and a full BOM though, assuming you're alright with that.
That's all cool. I don't care if you actually make a few trivial bucks here; it's just about fair use of IP, not any anti-capitalist ideology.
The last time I did something like this I sold off the boards above cost (though not by much); not as a money making endeavour as it hardly compensated my time invested (post office trips, filling out customs forms, blah, blah) but just to ensure that after sundry expenses (variations in postage costs to different countries, fuel for 6.3L car engine, etc) the endeavour wouldn't see me in the red.
Heck, if it means enabling half a dozen other members here to get duplicate builds up and running I think you could fairly recoup the cost of your own build; it would only be a knob that would get enviously or narky at you for that.
WoW very nice!!!
At university we had an HP scope (I don't remember model) with tetris, scope games are awesome
Machine vs machine ends at some point or goes to max freq and still playing?
+/-14.3V is just what the power supply delivers; will still operate fine on +/-15V rails. A 20V rating is adequate for the polarised caps.
Thanks! Seems like good advice. When you talk about a wide off center trace for TO-92, do you mean like would be used for "Ammo Pack" style pre-formed leads? Or do you mean more TO-18 style where the center pin is vertically off center from the other pads?
(for example, a 100uF TH tantalum costs between $3 and $5 from Digi-Key, whereas a surface mount version would be less than $1).
(for example, a 100uF TH tantalum costs between $3 and $5 from Digi-Key, whereas a surface mount version would be less than $1).
Aren't through-hole electrolytics the cheapest?
Question for GK, Should we be using electrolytics or tantalum caps in your circuit?
I know they slightly behave differently with ESR, voltage VS cap value and temperature.
Remember, you used to be able to purchase TO-92 with the center lead bent back already.
Ok, because of tape and reel, today, you have only these flavors A and B, C is rare: (All are top view)
A: (Too difficult to soldier on a home-made PCB)
000
B: (Easier to solder on a home-made PCB)
O O O
C: (Obsolete, but easiest to solder + you can get a fat 10 mil trace between the pads with good clearance):
2
O
O O
1 3
We would just end up purchasing type B and bend the center leg back, or type A and push it in like a tripod...
Careful, TO-18 might have pins 1&3 reversed, double check before blindly using that transistor footprint. Just use type B's footprint, modify the center pin by pushing it up by 2.54mm.
So, I had some time this afternoon while waiting for an appointment to redraw GK's trimmer diagram on my iPad in a vector drawing app. This is for inclusion on the schematic and possibly the silkscreen of the power supply board (since I'll have some free space there; it could also be done on the copper layer instead of silk, if those etching at home want it on their boards).
So, I had some time this afternoon while waiting for an appointment to redraw GK's trimmer diagram on my iPad in a vector drawing app. This is for inclusion on the schematic and possibly the silkscreen of the power supply board (since I'll have some free space there; it could also be done on the copper layer instead of silk, if those etching at home want it on their boards).
That looks good, but it might cause come confusion as the ball positions at the ends of "A" are not to scale as the circumference of the ball does not touch the boundary.
The only specified tantalum is the 100uF timing cap in the velocity integrator schematic. I specified tantalum here for the (generally) lower leakage as the capacitor is linearly charged with a rather small current (several uA). All of the other polarised capacitors can be electrolytic.
The 1uF integrator capacitors in the horizontal and vertical movement circuits shouldn't be some crappy Z5U/Y5V/etc dielectric and you probably wouldn't want to pay for COG/NPO here. The best pick is a TH polyester. 1uF is readily available in 5.08mm lead pitch in the required voltage rating range.
Similarly of the capacitors marked "*" "Polyester" in the function generator schematic can alternatively be COG/NPO ceramic types if going SMD as the capacitance values are small and the price relatively cheap - definitely do not substitute these with Z5U/Y5V or the like.
PET, being the most economical and physically compact (generally), is the logical choice.
Oh and don't forget test points. I would put lots of those solder in eyelet test points all over the circuit to allow for easy testing of the blocks as well as use test points on most interblock connections so that one can see how the circuit works.
For your trimmers, use vertical adjustable ones. This way, they don't need to be at the edge of the PCB, they can be easilly adjusted where ever you wish to position them. The vertical 10/25 turn trimmers also take less PCB space. Also, since you can't solder between the trimmer and top of the PCB, when wiring those, try to prioritize routing them on the bottom of the PCB.
I think timb's current rendered layout is just for space approximation at this point. To generate a nice 2 layer PCB without spaghetti traces, potentially creating some oscillators due to trace length looping around in odd ways, he will be forced to optimally re-arrange the components in each function block when routing.