Turning plants into capacitive sensors with tinyAVR

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A young Maker duo experiments with plants as a capacitive material.

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Copenhagen Institute of Interaction Design students Francesca Desmarais and Paula Te recently used tinyAVR microcontrollers to turn plants into capacitive sensors.

Using an ATTiny MCU with Arduino’s Capacitive Sensing Library, the Maker duo built a circuit that could be clipped onto plants. The closer another capacitive object got to the pot, such as one’s hand, the faster the LED would blink.

“We started out clipping the circuit to non-organic sensors like aluminum foil and metal cans to discover that surface area positively correlates with sensitivity. As we continued our experiments, we learned the importance of grounding both the to earth, so that both sensors share the same ground.”

Experimenting with plants as a capacitive material allowed the students to better understand capacitance and basic electronics on the atomic level. Interested in learning more? Head over to the project’s official page here.

Capacitive sensing with ancient keyboards

The Model M keyboard is a designation for a group of computer keyboards manufactured by IBM, Lexmark, Unicomp and MaxiSwitch, starting in 1984.

According to Wikipedia, the many variations of the keyboard have their own distinct characteristics, with the vast majority boasting a buckling spring key design and many having fully swappable keycaps.

As the venerable M keyboards are understandably ancient, there really is no easy method of connecting the device to a modern system. This unfortunate fact prompted a modder by the name of xwhatsit to ultimately build his own controller.

According to Hackaday’s Brian Benchoff, the beam spring keyboards use capacitive switches.

“With 122 keys, the usual method of reading capacitance – putting a capacitor in an oscillator – would be far too slow to be of any use in a keyboard. There is another method of reading capacitance: measuring the current going through the capacitive switch. This can easily be accomplished with an LM339 comparator,” he explained.

“xwhatsit‘s keyboard controller uses this capacitive sensing circuit to read the four rows of keys, with a few shift registers taking care of the columns. Atmel’s ATMega32u2 MCU is the brains of the outfit, running LUFA to translate the key presses to USB.”

Interested in learning more? Well, you’re in luck, because xwhatsit is selling Atmel based controllers for the Model M as well as the Model F using the same basic circuit.

Day 2: Atmel @ Embedded World

Day 2 of Embedded World 2014 in Nuremberg, Germany has drawn to a successful close. Our jam-packed booth hosted numerous journalists, analysts and industry insiders throughout an exciting day.

Atmel’s booth was also the site of several technical sessions, including embedded Internet technologies, web services and cloud computing, intelligent lighting control networks and ultra-low power system design.

In addition, we showcased a plethora of demos, including a lighting system with secure communication and cryptographic information exchange, capacitive sensing with dual functionality per button, car access systems, embedded microprocessors based on the ARM Cortex core, a battery-powered drill and anti-cloning protection.

Stay tuned for more Atmel Embedded World 2014 updates!

We’ll be back tomorrow for Day 3 of Embedded World in Nuremberg, Germany.