Step 6: Problems

Occasionally problems creep up.  A big problem popped up in this project when the first board was made.  No matter what was tried, the original design of having the board powered by button cell batteries with an on/off switch couldn’t work properly when finally assembled.  One of the problems wound up being an unacceptable voltage drop that made the battery source incompatible with one of the transistors chosen for the power circuit.  Many changes were tried to get the design to work, but nothing could be figured out without having to redesign the board, and since all of these boards were fabricated already, the decision had to be made to leave out the power circuit, give up on battery-sourced power, and requiring USB.  Very unfortunate, but this is why typically you order a small number of boards and work through some more testing.  Being short on time both because of the school year and free time led to the decision to hope it would work and get all the boards at once, and that gamble did not pay off.  The good news is that it works fine when plugged in to a power source via USB, so at least there is something to show for the project, even if it’s not 100% what the original design was for.  So as a result on the back of the board there are two pads for batteries and several smaller pads for the switch and other components (two transistors, two resistors, two diodes, and a capacitor).

Step 5: Testing

After the boards are made and programmed and any rework happens to fix any bugs, we’re good to go!  Testing along all points of the process is essential.  This last point came back to bite us, as explained next.

Step 4: Fabrication

Once the design is finalized we send that design off to be fabricated.  We use OSH Park for our board fabrication.  It takes a few weeks to produce the boards, and then you’ll get them in the mail.  At the same time we went and ordered all of the other components from Mouser, an electronics supplier.  Then the tedious task of making all of the boards happens.

Step 3: Technical Design

After it works, it needs to be translated into something that can be produced.  We used the Eagle CAD program to build our circuit and lay out our board.  It’s free for personal and educational use, so long as you don’t sell your work product.  There’s a bit of a learning curve, but there are also great tutorials out there. Once you’ve got an idea of the circuit, you create that circuit in the schematic view in Eagle.  Moving to the board view, it takes the schematic and drops those components into a space where you can move everything around to get the placement you want, and then draw the traces, or electrical connections, between all of the components.  Eagle contains a number of great troubleshooting tools that will tell you if your design violates rules that the board fabrication facility might have, and it will let you know if your finished product might not work as expected because things you don’t anticipate touching might accidentally touch.

Step 1: Design Idea

First a project needs to start with an idea. For this project, the idea was getting students interested in this process by showing how it’s possible to come up with an idea and turn it into a working product.  LCDS does a great job of instilling that concept in our students, this was an attempt to enhance that and give the students something they could program by themselves if they wanted, something tangible and easy to observe and experiment with.