“I love the idea of using bumper stickers as a form of self-expression, but I got to thinking about how ‘permanent’ they are, and how my own style, mood and taste tends to change relatively quickly,” he says. “I wanted to see how I could resolve those things – could I make a bumper sticker that was always up to date? Would it still be interesting if it wasn’t permanent?”
On track
Figuring a changeable bumper sticker would be both practical and fun, he initially decided to experiment by connecting a Raspberry Pi Zero 2 W computer to a 5-volt HDMI display before working out a way to gather and share information about the song he was currently listening to in near real-time. He figured the best method would be to connect the Raspberry Pi device to the internet and make use of the online music service Last.fm. “It’s a ‘scrobbling’ tool that you can use to keep track of everything you listen to, regardless of where you’re listening from,” Guy explains.
By connecting Spotify to his Last.fm account, Guy had a way of grabbing details about his most recently played tune. Raspberry Pi could then pull that information and send it to the display for others to view. Since he wanted his project to look like a bumper sticker, this entailed creating an easily updated graphic – one with black text on a yellow background – that could be easily updated with new details – and Guy came up with the idea of using an image file that could be produced and rendered just before it was shown.
To enable this, Guy turned to a social website called Val Town which allows developers to code in the cloud. He wrote a small chunk of code – referred to as a val – that would access and fetch his Last.fm profile to gather details of the last song he was listening to. He then, with the assistance of Val Town’s AI, wrote another val to use a Javascript HTML5 canvas library to lay out the bumper sticker using the information gathered. This involved a lot of trial and error to make the text fit correctly, but he was able to successfully create, export and display a PNG image without any manual intervention.
Driving forward
With the nuts and bolts of the project in place, it was time to start refining. “I always start with components I already have or already know how to use,” Guy says. “I then quickly get as close as I can to a finished version, and then I see if there are any deal-breakers or cheap and obvious ways to improve the design. I find that momentum, as well as the ability to see and feel a project early on, really helps me stay on track, even if I know I’m going to have to revise things.
Given the idea was to create a device that looked as much like a real bumper sticker as possible, Dupont swapped out the display for an 11.3-inch strip LCD. “Size, shape, and readability came before anything else,” he explained. Figuring he’d be drawing power from a 12-volt car battery, he also grabbed a couple of breakout connectors and a buck converter to knock the power down to five volts.
Initial plans to connect the Raspberry Pi computer to the internet using a hotspot on his phone were revised as well. Dupont realised that he’d need to manually connect Raspberry Pi to the hotspot every time he got into his car and he knew, in his heart of hearts, that he would eventually tire of doing this, causing him to eventually consign the project to a drawer. To avoid this situation, he utilised a Particle Baron IoT development board which he also happened to have lying around.
“The main advantage of the board versus using the phone as a hotspot is that I never have to touch it or remember to turn it on,” he says. The board connects to Raspberry Pi and uses cellular data, the bonus being there are no monthly fees. The data is limited in quantity, but there’s more than enough for Guy’s intended use which makes for a perfect fit. With everything working, it was then a case of installing it, which required a spot of in-car wiring – and some dismantling of the vehicle’s interior panels.
The right path
The Raspberry Pi and other components were affixed to the back of the display panel which was also fitted with magnets to allow the device to be easily secured to the back of the car. For a neat finish, the device was placed in a heat-shrink sleeve that happened to be the perfect size. A bit of cutting was then required to allow the screen to show through, and Guy used some glue around the cuts for weatherproofing.
It works well. Powered by the car battery as soon as the vehicle is turned on, it immediately connects to the internet, grabs the required information and displays it. “Honestly, everything went pretty smoothly with this build,” Guy said. “It’s funny, but the thing that held me up the most was trying to figure out which HDMI settings would make this oddball display show what I wanted it to!”
Guy particularly likes the fact that it’s entirely automated so he always knows that it’ll be displaying his songs when he tootling down the road. “It lives with the car, which also means the sticker continues to work even if my wife is driving,” he laughs. “I’m afraid to ask whether she thinks that’s a bug or feature!”
