Plotting Christmas gift tags using a Raspberry Pi and resin.io

On the first weekend of December, the fine folks from resin.io put on an Xmas IoT Hackathon at the London Fab Lab. The Fab Lab is a maker space for digital fabrication and rapid prototyping. They host classes and events (like hackathons) and members can use a variety of tools for wood and metal working as well as 3D printers and a laser cutter, which you can use e.g. to cut a gingerbread house like this one (made from real gingerbread!):

Appropriate to the occassion, the resin folks brought boxes full of hardware:

There was therefore no shortage of Raspberry Pis and all kinds of accessoires. Teams were formed and a range of exciting hacks started taking shape. I teamed up with Mark, a good friend and hackathon buddy, who had brought along a Graphtec Silhouette Portrait cutter/plotter which we were intending to hack:

You’d normally use this to cut out shapes previously created with their proprietary software Silhouette Studio. Of course that’s only the intended use. Replacing the knife by a silver sharpie turns the Silhouette into an electronic circuit plotter - for very simple circuits. Here’s a proof-of-concept circuit used to power an LCD with a button cell:

Our plan was to the Silhouette into a Christmas gift tag plotter, powered by a Raspberry Pi. Using Silhouette Studio to drive the plotter was of course no option. We had to find a pure command line, open source solution to generate the template and feed it to the plotter which also needed to run on the ARM processor of the Pi. After some searching and experimenting we found a Python based driver, which after a little tweaking was able to digest a postscript file and get it plotted. Here are some experimental results:

We generated the gift tags using paper.js: The user puts in five names of friends to create tags for and we place the names, framed each by two automatically generated snowflakes, on a canvas and have paper.js save the canvas as SVG. Now there were only two pieces missing: one was converting from svg to postscript, which inkscape happily does for us, even on the command line. The final piece was then a simple node.js server to put everything together: A form to put the names in, which when submitted generates an SVG string, which is POSTed to the server, where it is saved to a file, converted to postscript via inkscape and then fed to the plotter. Job done! Well, almost, we still had to deploy it to the Pi.

Fortunately resin.io, a deployment service for IoT devices, makes that rather simple: you create an application on the resin.io dashboard, download the base image for your device, flash it on the SD card, pop it into the Pi and boot it. After a few minutes the device comes online at the dashboard. When you then push to the Git repository associated with the project, your new code is deployed on the Pi, heroku-style, but cooler (because of the blue unicorn and cause it run on your device!).

The device is provisioned via docker and resin.io provide a base container (based on Raspbian wheezy) that comes with node.js preinstalled. Python, git and inkscape are easily installed via the apt package manager and we simply git clone the graphtec driver. The container automatically runs npm install and when successful npm start to run our server. So far, so straightforward, but there were two small issues to figure out: one was installing the font we were using for the names and refreshing the font cache and the other was detecting the printer, which required starting udevd manually. Having that sorted, our first test was finally sucessful:

We had a really great weekend at the Fab Lab and even made the 2nd prize with our hack. Thanks to the resin.io folks for putting it on and hopefully until the next one!