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As the Summer is winding down and the Fall semester is approaching, I'm beginning to think more about how I teach. To start practicing, I've started to produce brief educational videos called "The Short Circuit". The idea is for the videos to be short, instructional, (reasonably) well produced and yet frill free. My intention with the short circuit videos is to cover many topics in electrical engineering, but also keep the material connected. I've identified my definition of "The Learning Cycle," which I'll seek to implement in every video:

The open source phone by Dooba, called "Trill" is awesome. Open source PCB with a 3D printed enclosure. Beautiful little OLED display. Making a cellphone has been my objective for about a year - I even have most of the parts already. Sadly I haven't had the time to sit down and really work on it. But my cellphone is on it's last leg (And I've had it since 2012 - so it can be considered archaic at this point). I really don't want to buy another phone - so Trill is on my wishlist.

A look at the spindle slipping due to low contact friction with the holder, Z axis probing to prevent warpage, and counterweight springs to give a favorable failure mode for the spindle.

Z axis springs used to cancel the force of the spindle's weight
Z axis springs used to cancel the force of the spindle's weight

The demands of graduate school were taking their toll last month and I wasn't able to give OCI the love it deserves. But I'm back to work now! The Z axis was not getting enough current from the stepper driver on the ramps board. This is because the entire spindle assembly weighs 1kg - and is straining out the stepper motors. When moving in small increments, the motors will skip steps and move inconsistently (see data fromĀ Circuit Mill Development Log: Z Slip). Often times the spindle would slip downward while cutting, causing some catastrophic results.

Test geometric patterns and test designs milled with reasonable success

I've noticed that the circuit mill in development is having issues with small adjustments (0.3 mm). During small movements, the axis will do one of two things - it will either not move at all, or it will move too far. For example in the picture below, the left pattern was done keeping the Z axis at a steady height. The right pattern was done with the Z axis adjusting to keep the cut level. As you can see, the mill appears to be "slipping" over time, and the bit cuts further and further into the board.

No Z movement (left) vs Level compensation (right)

Here's a fun video showing all of the work that went in to prototyping, testing, and manufacturing television sets in the 1950's.

When designing any microcontroller (uC) based system, I find it can be a good idea to first plan out what signals are going to go to which pin on a the uC. Sitting down and filling out a document like the one pictured above can be a very efficient way to organize your thoughts and rap your head around your design. Your allocation document will also help when routing your schematic, PCB, when you are writing software, and when you are debugging. This document can be very valuable and is often overlooked!

A pin allocation planner for the Atmega32A

Currently the OCI standard is to use QUCS as a simulation environment, and KiCAD as a design environment. However wouldn't it be nice if everything could all be done with a single tool? Well that may be a possibility worth exploring. The CERN group has put some work into integrating SPICE into KiCAD. Just check out the video below!

Jay Carlson on his site jaycarlson.net has compiled an extremely comparative report of a wide range of 21 microcontrollers that are less than $1 USD. Selecting microcontrollers can be a daunting task and this acts as a great reference. Check out his work below!