Intelligent warning sign system utilising printed functionalities and hybrid integration

The direct medical care cost of all hospital treated injuries in the EU is estimated to be at least 78 billion Euros each year. Therefore, significant savings can be achieved in economical and human resources, when amount of injuries are decreased. Intelligent and active warning sign can prevent accidents more effectively than traditional passive graphical warning sign. Intelligent and active warning sign alerts person approaching potentially dangerous spot using both visual and audible warning. In areas without infrastructure, however, intelligent warning sign need to be autonomous. We have manufactured an intelligent and autonomous warning sign prototype utilising printed functionalities and hybrid integration. Our intelligent warning sign system utilises low energy radio network operating at 2.4 GHz ISM waveband in wireless communication. Radio system provides wireless link to other warning signs nearby and up and down gateway to server. In addition, system retains energy harvesting system based on flexible solar cell and bendable Li-Ion battery. Sensing is based on infrared sensor enabling person detection by emitted thermal radiation from 2 meter distance. Microcontroller decodes sensor signal and controls operations for warning signals based on six blinking LEDs and beeping buzzer. LED flexible substrate was PET foil on which conductive traces were printed using Asahi 411AW silver ink. Miniature high brightness 0402 size μSMD LEDs producing up to 50 mcd in ±65° angle were bonded on PET foil using isotropic conductive adhesive, type EPOTEK H20E. Final measures of the prototype were 75 mm × 220 mm with maximum thickness of 20 mm and weight of 58 grams. System assembly with rigid central part and flexible flanges enabled prototype attachment on flat, angulated or curved surfaces. Implemented warning sign system platform offers also possibility to implement other intelligent guiding and sensing information transmission applications in areas lacking connection to grid and wired Internet.