basic usb experimentor?

this is something I whipped up last night, a basic experimenter module for a 28 pin USB enabled pic, the 18F2550.

the board is very spartan, it contains usb connector, a few leds, reset and boot switch (as per microchip's usb bootloader spec), and pads for an inexpensive smt crystal series (avail in most common clock speeds).

one thing I'm not sure on yet is the usb connector itself. since this layout is on the top side of the pcb, the connector will cover the pads it needs to be soldered to. I'm thinking I'll swap the through-hole connector for an smt version, which will more or less have its leads exposed.

I would appreciate any on-topic thoughts and feedback from the community.

board layout:
**broken link removed**

schematic:
https://projects.dimension-x.net/pictures/usb/28pin_simple1_sch.png

Looks a bit like the **broken link removed**.

ah ha, yes it does. Those boards benefit from a double layer design, making them extra tiny

I'm not done shrinking mine down, right now the two rows of pins are spaced 1.2" apart (on a 100mil grid). Looks like they achieved 0.6" spacing, roughly the width of a 40pin pic!

It seems to me that people are too quick to shrink boards these days. Small boards are less expensive in quanity but I see a lot of hobby types shrinking boards for no good reason. A less dense board is easier to build and debug.

EDIT: I used the UBW as the basis for a USB to RS485 bridge/converter a few months ago.

Nice little board. Looks like you are using a double layer, with only one trace on the bottom? If this is the case, perhaps you could put vias right next to the pads for the USB connector, and connect to the bottom pads that way.
When I'm making a board at home, I open the DRC just before adding polygons, and open up all the spacing. This makes soldering without a solder mask much easier. (Looks like a pretty tight clearance between some tracks and the polygon - harder to solder without bridges.)

BeeBop said:

Nice little board. Looks like you are using a double layer, with only one trace on the bottom? If this is the case, perhaps you could put vias right next to the pads for the USB connector, and connect to the bottom pads that way.
When I'm making a board at home, I open the DRC just before adding polygons, and open up all the spacing. This makes soldering without a solder mask much easier. (Looks like a pretty tight clearance between some tracks and the polygon - harder to solder without bridges.)

Click to expand...

its really just single sided, the blue line and vias is just a symbol for a jumper to be soldered in later. the small image does make some of the clearances look bad, but printed out full size, everything has at least 12mil of clearance. (i ran the drc)

3v0; I agree... I sometimes spend way too much time obsessing on making something small, when I could have the project done already

my goal to shrink this down is to make it more usable on a breadboard. as it stands right now, 1.2" will fit in a standard double row breadboard, but you won't have access to any of the rows it plugs into. the UBW being only 0.6" fits nice into the center of a double row breadboard and leaves lots of room for wires and other components.

I may have to go with a true double sided layout to make it practical to fit on a breadboard.

as an update, I did shave 200 mils off the width, but it would still overlap all the rows on a double row breadboard. I also switched to an smt mini-b connector.

the way I solve that problem (general mixing of TH and SM components) is to put the TH component on the non-solder side. you need to be careful about clearance on the solder side when you mount the board.

justDIY said:

my goal to shrink this down is to make it more usable on a breadboard. as it stands right now, 1.2" will fit in a standard double row breadboard, but you won't have access to any of the rows it plugs into. the UBW being only 0.6" fits nice into the center of a double row breadboard and leaves lots of room for wires and other components.

Click to expand...

Just thinking here.
Your goal is to use it on a breadboard and are willing to go to a DS board.
Do have a reason for wanting to plug into both side of the breadboard?
How about putting a .1 right angle header on one edge of the board and bring all the signals out to it.
Your board would stand vertical on one side of the breadboard.
I would put a ICSP connector somewhere so I would not have to use breadboard connections for it.