Chris over at poweredbynerd.com speaks for all of us cash strapped gadget freaks:
Have the cash to snag yourself a fancy new CNC milling machine? Neither do I. Upon this sad realization, I’ve devised the means to explore the functions of a real CNC machine in my own lab, and more importantly, on the cheap.
Chris took one slightly battered Etch-a-Sketch, two unipolar stepper motors, and a handful of electronics and turned them into a virtual CNC machine called step-a-sketch.
The stepper motors are connected to the Etch-a-Sketch with short pieces of rubber fuel line which cleverly allows them to be easily connected and disconnected. They are in turn driven by a PIC processor via Motorola power MOSFETs. The PIC serves as the interface between a PC parallel port and the stepper motors. This PIC interface is as simple as possible. From the PC, the PIC receives a step and a direction signal for both X and Y, 4 wires total. The PIC firmware receives these signals and sequences them into the necessary signals for the stepper motor windings.
Improvements
Every gadget can be tweaked in some way… Here are a few ideas I had for this one.
The software on the PC that generates the step and direction data is unspecified. I recently wrote about RepRap, which is an open hardware 3D printer. The software for that project could possibly be ported and used here.
The PIC could be replaced, almost directly, with a stepper motor driver IC such as the L297.
If the microcontroller is kept, it could get new firmware that allows it to process GCODE or otherwise operate at a higher level, and interface directly with CAD software.
A good sized hobby motor with an off center weight attached to the shaft could serve as an automatic shaker to erase the last drawing before starting the next.
This project could be a novel new type of scope: GSO (graphite storage oscilloscope). While it would have very low bandwidth, the semi-nonvolatile storage it offers may prove useful in some niche applications.
Go take a look and be sure to watch the video.
Best regards,
Steve Ravet
EDN Gadgeteer
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