These smart audio guide flashlights are used by visitors under the Cathedral Square in Utrecht. By shining the flashlight on archaeological finds in the basement the flashlight automatically selects the correct audio fragment.

With a limited production of 30 smart flashlights, these flaslights are changed from a strong stock consumer model. The lamp and battery used in the stock flashlight are replaced by an efficient LED light and a lightweight lithium polymer battery. Additionally, the stock handle is replaced by a scope. This scope has two functions: to receive directional IR data and to attach a girdle.

For the archaeological remains small sensor points are produced that connect via ethernet to special sensor hubs. The hubs provide an unique ID for the sensor points that is broadcasted by infrared.

On the flashlight an IR transmitter and receiver are placed. By shining on a sensor point, the flashlight knows which audio file to play to the visitor's ear.

Workrange flashlight

0,5 m – 3 m
Longer range possible by changing scope configuration


STM32F407VGT6 microcontroller
32-bit ARM Cortex-M4F core
1 MB Flash
192 KB RAM


Lithium polymer


4500 mAh (2-cel)

Input / Output

1x Trigger
1x IR receiver (scope)
1x IR transmitter
1x LED light
2x LED button
1x ON/OFF switch
1x Volume


SD card for audio files