Pi-A-Sketch

Francois Dion is someone I exchange emails with every now and then. He’s the guy behind the excellent (and multilingual: check the site for posts and tutorials in English, French, Portuguese and Spanish) Raspberry Pi Python Adventures blog. He’s a hackspace member from North Carolina, and he’s been giving lecture-demonstrations of the Raspberry Pi (and lasers) to interested groups, and promoting it in schools locally. Our community would be nothing like as large and colourful as it is without people like Francois, who put their own time and energy into spreading the word about Raspberry Pi with no support from us at the Foundation – we are very, very grateful to Francois and all the other people out there who make so much effort on this project’s behalf. (Seriously; next time I’m in NC, I will be making a studied effort to fill Francois full of gratitude-symbolising food and drink. In as many languages as I can muster.)

Francois has been making something really cool.

circles on a greyscale display

Is it e-ink? No…

A little while ago, he attended a session at PyPTUG (the PYthon Piedmont Triad User Group) about motors. “We did a lot of stuff with motors. DC, servos, H bridges, PWM and steppers. It was a very dense 3 hours. We covered a lot, and it was a lot of fun.” He went away to think deep thoughts about what sort of fun you could have with a Pi and some stepper motors; and he came up with the Pi-A-Sketch.

Pi-a-Sketch set up, stepper motors visible

The stepper motors you can see here have the same diameter as the shaft of the familiar twirly knob they replace.

Equipped with an Etch-a-Sketch, some stepper motors, a battery pack, a Pi, an 8-channel Darlington pair and some leds, wires and headers, Francois has made a device that uses Python to draw all those things on an Etch-a-Sketch that, as kids, had us throwing the things at the floor in frustration at the uselessness of our fat thumbs. Horizontal, vertical and diagonal lines? No problem. And with a bit of help from Bresenham’s algorithm, you can draw circles too. (Eben has a funny story from when he was about 11 which involves Bresenham’s algorithm, a BBC Micro, the days before the internet, inter-library loans and the month’s wait he had to endure before he was able to get his hands on the very simple information he needed to draw a line on the screen. Ask him about it if you see him and you need a reminder of how lucky we are to have the ability to look this stuff up online.)

“What practical use is all this?” I hear you mutter at the screen. Well, so far it’s gone down a treat at talks Francois has been giving about the Pi and programming. This sort of demonstration is exactly the sort of thing that captures the imagination, and opens up the eyes to what you can achieve with a little programming and a little solder flux. Here’s something familiar that you can pass around an audience (thanks to that Kodak battery pack), made magical with the addition of a little science. We love it, and so did the audience at the IEEE in Winston Salem, NC, where Francois first showed this project off.

Circles and lines on Etch-a-Sketch panel

Instructions on how to get the hardware set up are available at Raspberry Pi Python Adventures, and Francois will also be writing a post about the Python that you’ll need to get things working in the next few days. (I’ll update this post when he’s ready – in the meantime, you can find the source code at Bitbucket.) Thanks Francois; we look forward to hearing more from you!

 

14 comments

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Clearly the next step is to make a console framebuffer driver.

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clearly!

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You may be like me and suffer from inkjet printer rage, it’s a more common medical condition than you might think. After you have finished fixing your printer with the hammer you should find you have two useful stepper motors amongst the debris ( paper drive and print head drive ). Stepper motors can be pricey when bought from hobby shops but are very handy for all sorts of projects that need accurate motor control.

To reduce inkjet printer rage, try a colour laser printer and welcome calm back into your life.

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I find it quite odd that steppers motors are so pricey. Don’t floppy drives have stepper motors? They are dirt cheap!

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Ha ha, I remember trying to print some wedding invites on a sailing vessel only to go into printer rage and launched it off the back of the boat. Not good for the greenies but certainly made me feel better. So yes, please recycle the parts although its kind of neat knowing some little fish have made 20th century tech their new home albeit in technicolour.

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Thats my board mounted in that Pi and my stepper motors ! You can see them at MyPiShop.com (Underconstruction) or buy them on ebay (Search “raspberry stepper gpio”).

NICE application.

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Don’t get me started on printers! Immediately raises my blood pressure.
They could be useful but the greedy money grabbers try to squeeze every last penny out of you
(but not from their ink catridges). Best example: My Canon printer refuses to print black-and-white pages if a colour cartridge is empty!
Did you know that most printers use more ink when they are switched on and then perform ‘calibration’ (Ha!) then printing 10 pages! I leave mine on. The electricity cost is a fraction of the ink costs.

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Reminds me of a Dilbert cartoon:

http://dilbert.com/strips/comic/1995-04-03/

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Liz, I also have a funny story about implementing Bresenham’s circle drawing algorithm in the pre-internet era although I didn’t have interlibrary loan available as I didn’t have the luxury of waiting so long for stuff to arrive so it was a quick trip from Leicester to London to spend an hour or two in Foyle’s notebook & pencil in hand that eded up being a right comedy of errors and what was supposed to be a day trip ended up being a week

liz

S’funny – you get so used to being able to look stuff up instantly now, but it was *awful* back in the day when you heard about something useful (like Bresenham’s algorithm) or could’t *quite* remember something, and either had to give up entirely, or rifle through the library (and possibly end up waiting a month for a book). I lived 20 miles away from the nearest decent library when I was a kid. Thank Jimbo for Wikipedia.

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yes. i was lucky because i managed to wangle a reader card from our local uni & poly & on the whole our local library system was pretty good but as some of my interests were a bit weird you’d often find me at Blackwell’s or Foyle’s reading the words off the page & surreptitiously making copious notes for later use. what i wouldn’t have given for a handheld scanner in those days

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Ok, who else would kill for a program that interfaces with this hardware and could take a picture you feed it and put it on the etch-a-sketch?

Ok, maybe not kill, but how completely awesome would it be to give an etch-a-sketch as a gift with someone’s picture on it, or something similar? I swear I’ve seen somewhere on the internet that will do that for you, but it costs a small fortune.

-dave

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Was it Mitchener Algorithm to draw circles/ellipses?

Fun!

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There’s an update video, shot at 1080p instead of 720, but then scaled down to 720p using the computer. Seems that works 1000x better at capturing the black on grey of the Etch-A-Sketch:

improved pi-a-sketch video

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