Home > BrewzNET 2.0, Tech geeks > Designing and Ordering PCBs

Designing and Ordering PCBs

This long weekend I spent some time getting re-acquainted with Eagle, which has had several new versions since I last used it. It’s a powerful and full-featured software tool for designing circuit boards, and best of all there are versions of it that are free for hobby and non-profit use. When you combine that program with online Printed Circuit Board (PCB) services like OSH Park, it is extremely easy for someone to design custom electronics like my BrewzNET stuff. I’ll try not to make this post too technical in the off chance you want to read more than just the first paragraph.

LCD SchematicPCB design starts with a “schematic”. These are basically abstract drawings that show the various components in your circuit and how they are hooked together. The first one I tackled was the board that interfaces my liquid crystal display (LCD) with the microcontroller. The heart of the circuit is the MCP23017 digital input/output expander chip. This component connects to several different points where I can attach switches (all of the GPA* pins), as well as to the LCD screen (all of the GPB* pins). There are a couple of resistors here and there to keep signals trued up to the correct voltage. There is also an additional chip called an EEPROM that is used to store system settings. The EEPROM is sitting on this board with the LCD because it shares the same communication protocol with the microcontroller, called I2C. The schematic is created by selecting components out of the Eagle component libraries and then wiring them together using the green lines.

LCD BoardOnce the schematic is complete it can be converted over to a PCB board using a menu item. Initially the board is blank and all the components are set off to the side, and it is up to you to drag them on to the board, position them the way you want, and begin “wiring” the components up. There is even an “Autorouter” tool that will do most of the routing work for you, and you can go back after to clean things up if required. The red lines are the “traces” (wires) on the top of the board, while the blue ones are on the bottom side of the board. The white and gray colored shapes show the orientation of the various components, and the green circles and ovals are the “pads” where the components are soldered on. I’ve also added some text in places to help identify the intended use of the components.

LCD TopLCD BottomWhen the PCB layout is all done, you’ve double-checked all the connections against your prototype circuit and the datasheets, and you want to get a prototype made – that’s where outfits like OSH Park come in. They will take the output from Eagle (and in the case of OSH Park, they use the Eagle 6.5 board file directly) and convert it into the information they require to manufacture your circuit. For my LCD interface board it’s less than $20 and I get 3 copies. They professionally etch and silkscreen the board in a large “panel” with many other designs, cut the panel into the individual pieces, and send you your copies in 2-3 weeks. The reason for the long turnaround I believe is that they are being manufactured in Asia and take a little while to find their way back to the US. In my case, I submitted them this morning (Feb 17) and they should be back sometime around March 1 (plus a couple days for USPS to deliver them to me).

I really hope this first run with OSH Park goes well. Getting low-cost professional boards (even if it takes some time) beats the heck of wrestling with printing the traces, etching boards, ironing on silkscreen layers, cutting the boards down, drilling all of the holes out by hand… I did that for the first version of BrewzNET back in 2008 and while it worked, it was very laborious and was not pretty. It also has health hazards associated with it (fiberglass dust from drilling the holes, the corrosive etchant used to make the boards…) so a commercial avenue to have this work done for me sounds much more appealing for multiple reasons.

Categories: BrewzNET 2.0, Tech geeks
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  1. March 14, 2014 at 6:24 pm
  2. March 15, 2014 at 7:56 pm

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