To my non-ECE friends: Sorry this post won’t make any sense. Please stop reading now :).
My next project – a 100Msps/20-40MHz USB Oscilloscope.
I’m making it mainly to learn about a few things – high speed circuitry (EVERYTHING becomes a capacitor + inductor, and 45 degrees bent traces are better than 90), some more VHDL with FPGA, and making my own PCB!
The PCB making part I’m most excited about. If you don’t know already, some companies will make “prototype” PCBs for you for ~$20-$30. Just need to draw your PCB in an electrical CAD program (gEDA, EAGLE, KiCAD, etc), and send them the file along with your credit card details. Wait a few days/weeks, and you’ll get your little green board in the mail, professionally made.
There are ways to make your own PCBs at home, using smelly chemicals and hand drills, but for $20-$30, I would just get someone to make it for me. No need to deal with nasty chemicals, and MUCH higher quality.
One very popular and the cheapest prototyping service is BatchPCB. $10 setup/handling + $2.5 / sq in for 2 layers board (you can have traces and components on both sides). Apparently quality is pretty good. Downside is it takes forever (up to more than a month).
The other one I’m considering is Olimex. EUR 30 (~$40) for a 16cm*10cm panel (HUGE!). You can divide it up any way you want. Cheaper if you are making bigger boards, or need more than one board. 3-5 days turnaround time. If you want to make some PCBs too maybe we can share a panel?
One major advantage of making a PCB vs breadboard/prototyping board is surface mount chips. All the fun chips (FPGAs, newer microcontrollers, USB interface chips, etc) are only available in surface mount packages. Contrarily to popular beliefs, it IS possible to hand-solder SMD chips. I’ve successfully soldered a 28-pin TSSOP. It’s pain in the rear end, but doable with a clean, fine soldering tip with a lot of flux, and mad soldering skills of course :). QFP should be similar (same lead spacing, just on 4 sides). I wouldn’t try QFN, though, I heard they are very hard due to the lack of extended leads. SOIC should be very easy due to huge lead spacing.
That’s about all the common chip packages.
DIP (the kind we used in labs, very easy to solder) –
As you can see, most ARE actually hand solderable. Just need to make your own PCB.
Some chips with hundreds of pins (huge FPGAs, microprocessors, etc) use other packages like BGA or LGA (where the pins form a “grid”). I’m not worrying about those yet =P. Even the newest FPGAs are available in QFP (at least the smaller ones).
There are many tutorials online for SMD hand soldering.
Coincidentally, there’s an article in IEEE Spectrum about this exact same topic.
(The picture above was stolen from there shamelessly :)).
(BTW, the segway project has been put on hold until I learn more about control theory next year… right now it’s able to balance itself for a second or 2 before falling down. I think it’s to do with the large delay in the PID feedback loop, but I don’t know what to do with it yet =P)