Instrumentation amp protoboard rev2.1

Revision 2.1 of the instrumentation amp protoboard. This version allows the screw terminals for Gnd input to be disconnected from the board Gnd when a barrel connector is plugged in, or not, depending on jumper wires.

In Instrumentation amp protoboard, I showed an earlier draft design for the instrumentation amp protoboard. After tweaking the design a bit, I think I’m ready to try fabricating it.

I’m planning to try fabricating through iteadstudio this time, since they have the cheapest rates I’ve found yet: 10 boards for $9.90 + $3.90 shipping, for only $13.80.  Of course, the shipping is from China, so even air mail may take a while, and I don’t know what their turnaround time is for orders.  They also have small-batch orders that are even cheaper: $45 for 50 boards, $75 for 100 boards, making this very attractive for classroom use.  Of course, if the board gets just a tiny bit bigger, the price doubles or quadruples, since they have a 5cm×5cm bounding box for this price.

This will be the 4th different PCB prototype service I’ve tried. The others are 4pcb.com (good service, USA made, but a bit pricey), batchPCB (a little slower, but cheaper, probably from China), and OSH Park (USA made, cheap if boards are tiny or you need 3 copies , accepts Eagle brd file, don’t know how fast yet).

I think that someone using Eagle for design might do best with OSH Park, since learning how to use Eagle to produce the Gerber files needed by the other fab houses was a bit of a pain.

iteadstudio does provide Eagle design-rule check and CAM files, but they seem to be pretty much the same as the default Eagle ones—I’ve not gone through them carefully to see if there are any subtle changes.  They do have the most awkward way for delivering the Gerber files, requiring that they be e-mailed as a zip file, rather than accepting upload over the web like the other services.

Worksheet for designing layout. This PNG image is a little small, but Eagle can make a PDF output that is big enough for easy layout.

I improved the top documentation layer, so that the combination of the documentation and top silkscreen make a useful worksheet for students to design their layout on. If printed at 3.5× real size, the worksheet fits nicely on a page and leaves room in each resistor for adding a value.

I tried a couple of slightly different layouts for the EKG blinky circuit with optional Arduino output, and it seems to be fairly easy to lay out.  The hard parts for students will be coming up with the circuit design and soldering it up without shorting adjacent pads.

I’ll have to write up some documentation for the board, to explain the options for power (from an Arduino, from a DC power barrel, or from screw terminals; whether an RC filter is added to the power input or not; where the power and Gnd connections are available on the board, …).  I’ll probably also have to write some assembly/soldering instructions for the parts of the board that aren’t student customized.