This week I started with the step-response "HelloTxRx" board and wanted to reconfigure it to be able to measure how full a glass of liquid is. I also wanted to improve on the design by adding a crystal for better timing, and use CAD in conjunction with EAGLE. Seemed simple enough....
I started by creating the diagram in EagleCAD and adding in my improvements. This part proved to be the most challenging as there was nowhere to put a generic copper sensor. Since the sensor is just some pads of any shape, EagleCAD doesn't really have tools to approximate that. I got turned around quite a bit with thinking about this project because one of the pads has both 5V+ and GND going to it, and I kept thinking this is a short circuit.
I finally worked it all out and created the upper part of the board. I exported this to Rhino for the cad. The intention was to cut the pads on the vinyl cutter out of a roll of copper to save myself some milling time, then composite that with the board. I had a lot of issues with the vinyl cutter because the Linux partition was down and printing directly from Illustrator to the vinyl cutter left me with relatively zero control.
Here is what it should look like if it was milled on one board all at once. Ideal!
HelloTxRx Program. Language: C
HelloTxRx MakeFile. Language: C
HelloTxRx Python. Language: C
Vinyl Cutter Errors. Going too fast made the traces rip up. This is what made me change the idea to a 2 piece board.
Errors on the cutter again. In theory this should work, but I was not having any luck.
Cutting the copper on the Vinyl Cutter. I used transfer paper to transfer the copper to the backerboard, and placed clear transfer plastic on the backer for insulation. I cut the aluminum backer plate at Autodesk BuildSpace on the waterjet.
Mock-up of the board without the surface mounted components.
Starting to solder the components onto the board.
Here is the completed Beer Coaster! And suprise suprise, it didn't work.
I went back and created two more boards and used the TxRx Step-Response board Niel posted, and it worked.
Glamour Shot. Next steps: Add a battery. Add wifi. Add RGB LED. Add solar top.... The goal would be to have your coaster Tweet when you need a new glass of liquid.