813 Optoelectronics

Open

Open

Photo transistor circuit

LED circuit

Photo transistor circuit

To speedometer cable

Light shielding plate

To speedometer cable

Photocoupler

Fig. 8.25 An optocoupler

Light shielding plate

Photocoupler

Fig. 8.25 An optocoupler the steering position sensor, or a vehicle speed sensor. Light from the LED is directed onto the phototransistor and this affects the output from the transistor. When the light from the LED is interrupted by an opaque object the transistor output changes. The interruption of the light from the LED is achieved by the rotation, between the LED and the transistor, of a disc with holes in it.

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