Board Design Sanity Check

So things have been a bit quiet lately while I was focused on designing an Arduino shield based on my stripboard prototype. This includes:

  • Arduino shield pattern for easy mounting
  • 25-key matrix with diodes on all switches to minimize ghosting problems
  • headers and trimpot for connecting a standard parallel LCD
  • header for encoder +5V, GND, PhaseA, PhaseB

I decided not to incorporate any encoder-specific circuitry so people could pick their own. There’s a wide variety and this design pretty much just provides power and the two Arduino interrupt pins on a header so you can roll however you want. My Grayhill encoder needs a couple resistors which can be attached on any little bit of stripboard.

I’ve attached a couple of PDFs with the schematic and board layout. If anyone finds any bugs, please leave a comment. I’m going to order one or two boards this week to verify the design, and then I’m planning to order a small batch of a dozen or so which should sell for ~$15-20 or so just to cover my costs. Any commenters will get dibs on the first boards of course!

Looking towards a final version, I’m seeing a cost breakdown something like this, based on single-piece retail pricing for the components:

  • Arduino board: $30
  • Encoder: $26
  • LCD Module: $18
  • Raw PCB: $17
  • Small components: $15 (switches, pin headers, resistors, diodes, etc.)

That gets you to a total price of $106. The Arduino is optional if you have one already, and you could omit the LCD as well, but it’s pretty cheap for what it gives you. If there’s demand, though, I might do a different design either with more keys or with LEDs for more simple feedback. Another option is to go with either a cheaper encoder (I’m testing a $3 Panasonic one now) or a more expensive one made for use as an MPG.

I’m also starting to design out an enclosure strategy for this. One lesson I’ve learned over and over is that the least fun part of most electronics projects is finding a place to put the $#@! board. This project by its intended use really demands a well thought-out approach in order to be usable. I’ve seen some nice “grabber” hand-held instrument cases for about $30.

Where all this gets interesting is if demand is decent, I might look to offer complete parts kits. As it is, the parts for this come from at least three different places, so you’re going to get hit with close to $30 in shipping and handling charges. If I could order in quantities to do at least 25 at a time, it would make it possible to do a full kit for the same or less than buying all the parts yourself, and of course save the hassle of navigating the Mouser and Digikey ordering systems. So if you’re interested, please leave a comment–no commitment!

Schematic (PDF)
Board (PDF)

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4 responses to “Board Design Sanity Check

  1. Bill December 29, 2010 at 9:10 pm

    I would be interested in buying one, preferably a complete kit, but I can do the digikey thing just as easy. Sorry I can’t comment on the schematic, that’s not my forte, but soldering up a kit is no problem.

  2. Phil January 12, 2011 at 2:33 pm

    I am definitely interested. I’ll have to bookmark you blog and keep up on your progress.

  3. Mike McPherson February 14, 2011 at 5:51 am

    I wonder if it’s worth adding smoothing capacitor(s) across the supply to the encoder?

    nice design though!

    cheers
    Mike

  4. Mike McPherson February 14, 2011 at 5:55 am

    PS
    meant to add
    I already have an Arduino UNO gcode interpreter running
    It’s based on the RepRap and its friends but I have made it more robust and added a gcode feeder program that passes the code over USB with parity checking and error correction
    it also has a PCB milling front end so you can visualise what’s (meane to be) happening!
    happy to post it if you like

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