US Patent 8082922 Head-up display unit

A head-up display unit 10 comprises a microprocessor 30 which controls four light-emitting diodes (LEDs) which constitute the head-up display 20. The microprocessor 30 and LEDs 20 are powered by a battery 40 and a switch 50 is in series with the battery. A temporary store 60 in the form of a capacitor is in parallel with the battery 40 after the switch 50. A data receiver 32 is connected to the microprocessor 30 and communicates received data 34 to the microprocessor 30. The head-up display unit 10 is located in the face-mask 100 of a self contained breathing apparatus unit. The LEDs 20 are located in the periphery of the viewable region of the face-mask 100 so that they can be seen by the user when the face-mask is worn. The switch 50 comprises two conductive rubber strips which conduct current between them when sufficient pressure is applied. The switch 50 is located on a portion of the face-mask seal 102 such that when the face-mask 100 is worn i.e. held against the face of the wearer, the rubber strips conduct current between them and when the face-mask is not being worn the rubber strips do not conduct. The switch 50 is embedded in the face-mask seal 102 in such a way that a tight seal between the user and the face-mask 100 is still achieved when the face-mask is worn.