Device having an optically sensitive input element
The device has an input element, which can be used for resetting the device. The input element has at least one first photodiode arranged in series to at least one second photodiode. A voltage is applied over the photodiodes. When the user blocks light to only the second photodiode, the voltage at the interconnection between the photodiodes changes, which can be used to trigger the input element. The input element has low power consumption and high reliability.
1. A device comprising a housing ( 1 ) and a user-operatable input element ( 14 ), wherein said input element ( 14 ) comprises at least one photodiode (D 1 , D 2 a, D 2 b ), characterized in that said input element ( 14 ) comprises
a sensing circuit ( 15 ) comprising at least one first photodiode (D 1 ) and at least one second photo-diode (D 2 a, D 2 b ), wherein said first photodiode (D 1 ) is arranged in series to said second photodiode (D 2 a, D 2 b ), a voltage source ( 12 ) generating a voltage, wherein said voltage is applied over said sensing circuit ( 15 ),
an amplifier (A 1 ) having an input connected to an intermediate voltage potential at a location ( 16 ) between said first photodiode (D 1 ) and said second photodiode (D 2 a, D 2 b ),
wherein said first photodiode (D 1 ) and said second photodiode (D 2 a , D 2 b ) are spaced apart and are arranged to receive ambient light at least in part through first and second separate areas ( 6 , 7 ) of said housing ( 1 ); and
wherein the input of said amplifier is connected via a low-pass filter ( 17 ) to a location ( 16 ) between the first photodiode (DI) and the second photodiode (D 2 a, D 2 b ), said low-pass filter ( 17 ) comprising a capacitor (CI) and an asymmetric resistor (R 1 , D 3 ), wherein said asymmetric resister (R 1 ,D 3 ) is arranged between said capacitor (CI) and said location ( 16 ) and is oriented to have a higher conductivity for current flowing through said second photodiode (D 2 a, D 2 b ) than for current flowing through said first photodiode (DI).
2. The device of claim 1 wherein said first photodiode (D 1 ) or photodiodes has/have a total first responsivity and said second photodiode (D 2 a, D 2 b ) or photodiodes has/have a total second responsivity, wherein said first responsivity is smaller than said second responsivity, in particular wherein, said first responsivity is no more than 50% of said second responsivity.
3. The device of claim 1 , wherein there are more second photodiodes (D 2 a, D 2 b ) than first photodiodes (D 1 ).
4. The device of claim 1 , wherein there is one first photodiode (D 1 ) and there are two second photodiodes (D 2 a, D 2 b ), wherein said photodiodes are of identical design.
5. The device of claim 1 , wherein there is exactly one first and exactly one second photodiode (D 2 a, D 2 b ), with the first photodiode (D 1 ) having a smaller individual responsivity than the second photodiode (D 2 a, D 2 b ).
6. The device of claim 1 , wherein a center of said first area ( 6 ) is at a distance of at least 0.5 cm, in particular of at least 1 cm, from a center of said second area ( 7 ).
7. The device of claim 1 , wherein a center of said first area ( 6 ) is at a distance of no more than 5 cm, in particular of no more than 2 cm, from a center of said second area ( 7 ).
8. The device of claim 1 , wherein said first area ( 6 ) and said second area ( 7 ) are arranged on a common side of the housing ( 1 ).
9. The device of claim 8 comprising a fixation device for fixing said housing ( 1 ) against a human or animal body with said common side facing said body.
10. The device of claim 1 , further comprising a control unit ( 10 ) for controlling an operation of the device as well as a reset circuit for resetting said control unit, wherein said reset circuit comprises said input element ( 14 ) for triggering a reset.
11. The device of claim 1 , wherein said first photodiode (D 1 ) is at a distance of at least 0.5 cm, in particular of at least 1 cm, from a said second photodiode (D 2 a, D 2 b ).
12. The device of claim 1 , wherein said asymmetric resistor comprises an ohmic resistor and a diode, arranged in parallel to each other.
13. The device of claim 1 , wherein said housing ( 1 ) comprises at least one window, wherein said photodiodes (D 1 ; D 2 a, D 2 b ) are located behind said at least one window.
14. The device of claim 13 , wherein said housing ( 1 ) comprises a first window and a second window, with said at least one first photodiode (D 1 ) located behind the first window and said at least one second photodiode (D 2 a, D 2 b ) arranged behind the second window.
15. The device of claim 1 , wherein said separate areas ( 6 , 7 ) of the housing are provided with at least one visually perceptible marking ( 8 ) allowing a user to distinguish between them.
16. The device of claim 1 , further comprising a shield ( 21 ) optically separating said first and said second photodiodes (D 1 , D 2 a , D 2 b ) and preventing light entering through said first area ( 6 ) from reaching said at least one second photodiode (D 2 a, D 2 b ) and for preventing light entering through said second area ( 7 ) from reaching said at least one first photo-diode (D 1 ).
17. The device of claim 1 , further comprising a non-transparent cover ( 22 ) for preventing light from reaching said at least one second photodiode (D 2 a, D 2 b ).
18. The device of claim 17 , where in said cover ( 22 ) is affixed to said housing ( 1 ) and moveable in respect to said housing ( 1 ) or reversely removable from said housing ( 1 ).
19. The device of claim 17 , wherein said housing ( 1 ) comprises a battery compartment ( 23 ) and wherein said cover ( 22 ) forms a lid of said battery compartment ( 23 ).