Solar Powered Light and Temperature
Sensitive Interactive Sculpture


(click images for better view)


A blend of technology and art, this is not just any blinking light. The Picaxe microcontroller constantly records room temperature as detected by the DS18B20 onewire temperature sensor. An array of recently recorded temperatures is used to determine the minimum and maximum values over the last few minutes. From this, the most recent value is autoscaled and the bi-color LED eyes pulsate with an indicative color somewhere between green (coolest) and red (warmest).

To make the sculpture more interesting (both electronically, and to the viewer), the LEDs are also used for continuous detection of ambient light. You read that right... In addition to generating light in this circuit, the LEDs are also used to sense light. When the detected light change is above a threshold, the sculpture pulsates faster and uses a smaller recorded temperature array. Shade the eyes for a second and the sculpture starts pulsating at 1 second intervals. Now the viewer can easily control the eye color by heating or cooling the temperature sensor slightly by simply blowing on it or touching it. A 0.1 degree change is sufficient to make the complete eye color transition. After a period of disuse, the blinking slows back down to a slower rate (approx once every 15 seconds) to preserve battery power.

The robot body is constructed of old UV sensitive EPROMS with a really nice clear-windowed chip for the thorax. Viewers usually don’t appreciate the layers of engineering which allow something like this to be built (e.g. digital logic, microcontrollers, ADCs, etc.). However, I’ve been told that the sculpture body is cute (well, cuter than a real robot) and the fact that the eye color actually means something is icing on the cake. Explaining that the sculpture is in-circuit programmable hasn’t been worth the hassle except to the EE minded, since the shock and awe of a blinking light on a humanoid shaped body usually seems sufficient.

Power is supplied by 2 rechargeable AA’s which are constantly charging via a small 3.6V solar cell supported by connecting wire; simple but adequate. Who wants to have to change batteries in a sculpture?

Parts List:

Picaxe 08M microcontroller
DS18B20 temperature sensor
3-Lead Bi-color LEDs (2)
220K resistors (2) - to current limit the LEDs
3 pin programming header
10K resistor
220K resistor
AAAx2 battery holder
AAA NiMH battery (2)
3.6v solar cell


The thing I love about these picaxe projects is that the design and assembly is pretty minimalist. As the schematic shows, just hook the bi-color LEDs and the DS18B20 to the Picaxe, program the chip, and you're done. Use your imagination for the body. Old computer ICs hotglued together in any configuration could be interesting.

The software for this sculpture is fairly straightforward. Recording a continuous loop of data in such a limited chip took a bit of planning. Code memory is pretty limited, so I find myself constantly rewriting bits of code in order to squeeze just one more feature into the device. Since software allows for infinite flexibility, coding is never complete; it just reaches ever higher plateaus of acceptability.

And this software uses the same circuit for a slightly different behavior. It pulses a random color between red and green, and occasionally indicates the temperature in morse-code encoded flashing.

This code is explicitly released under the GPL. And this page is licensed under a Creative Commons Attribution 2.5 License.  

Write me if you find this project interesting. Link to this page if you find it relevant.

Warning, warmly greet new renewably powered interactive autonomous electromechanical overlords. This project is provided without any warranty and probably isn't suitable for anything.

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