Prototype for an Outdoor sensor interface


This is our latest adventure from the Blue Mountains, Australia. It’s such an exciting project we decided to blog about it.

We’re making an outdoor interactive sound installation that will locate five separate sensor interfaces hidden in and around the trees in a public location. In essence, we’re surrounding various trees with some great technology to tell (whisper) a story whenever someone passes by. Our blogging for now is about the technicalities of prototyping this project.

Here is a signal flow & component chart for the prototype so far.


So what are we trying to do …..

What are we trying to do? We’re aiming to surprise and inspire the passer-by (accidental or otherwise). To engage them in a somewhat heightened awareness of their immediate surroundings and the stories they hold, as if the trees or the nature in their world has a voice … It’s also a variation of the old thought experiment “If a tree falls in a forest and no one is around to hear it, does it make a sound?”. If no one walks past the tree, does it make a sound ? ….

Technically there’s nothing unusual about the project except that we want the random passer-by to trigger high quality audio from an invisible source, which is something we’ve never done before. The challenge for us is that the installation is outdoors, not very far from traffic, and needs to be somewhat self-sufficient for the duration (somewhat being the loose operative word here).

The installation will be up for three weeks. All of the technical components will be powered by just one Lithium battery, which needs to remain charged for at least 3 to 4 days, so we can pop in discretely and replace it, or alternatively, use a small solar panel so it’s truly self-sufficient, but then it gets harder to make the unit invisible, or at least discrete. Apart from the outdoor speaker (and possibly solar panel) all of the technology will be housed in a small waterproof case and installed in a moist, urban, late autumn, mountain environment for up to three weeks.

While we’re prototyping the interface(s) we want to blog about the process, (meet Post 1), and we want to share the results of our experience.

Prototyping Project components

We’re working with the Wave Shield v1.1 kit from the excellent Adafruit Industries, to add the audio playback to an Arduino Uno R3  (Arduino), which will then be triggered by the sensor.  What we really like about the Wave Shield is that it’s powered via the Arduino, unlike other audio shields that require their own separate power (and yep, power is our challenge here). The audio level  from the waveshield is too low for our purposes, but adding a 2.5W mono amp makes a major difference and is totally adequate. It’s a really small component so well within our physical space requirements.

At the moment, we’re experimenting with 4 sensors; two long range IF SHARP 2Y0A02 F 4Y & GP2Y0A710K0F distance sensors, an Ultrasonic ranging module HC-SR04 and an Ultrasonic range finder – Maxbotix LV-Maxsonar-EZ1. Fortunately, us lot in the antipodes of all things Adafruit / Arduino have some excellent suppliers in our neck of the woods: Tronixlabs, Little Bird Electronics and Radio Parts.

The first two sensors we’ve tried (the first Sharp IF and the HC-SR04) are working with the Wave Shield and Arduino Uno but are the wrong sensors for this project. The IF triggers from unexpected light variation and the HC-SR04 triggers from too wide an angle. Our next step is to test the Ultrasonic range finder – Maxbotix LV-MaxSonar-EZ Series (the EZ1) (so far so fantastic) and another Sharp GP2Y0A710K Distance Sensor (100 – 550cm).

Next step is to get a bigger Lithium battery, make another Wave Shield, hook up the solar panel, put everything in the box and test it outside.

More to come …

There’s a lot more info about the Adafruit Wave Shield and building the board for a project like ours out there. We found this link really useful, it’s from the Digital + Media Rhode Island School of Design website, and Adafruit have an excellent forum.

Here are some images of the prototype so far …

1) The first test with the SHARP 2Y0A02 F 4Y Infra Red Sensor


2) The second test with the Ultrasonic ranging module HC-SR04 (nice carpet right?)


3) The third and most successful and accurate test with Maxbotix LV-Maxsonar-EZ1


One thought on “Prototype for an Outdoor sensor interface”

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