Three LEDs signal bumper-barrier distance, Infra-red operation, indoor use This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall. All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity. Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc. Circuit diagram: Park-Aid Circuit Diagram Parts: R1_____________10K 1/4W Resistor R2,R5,R6,R9_____1K 1/4W Resistors R3_____________33R 1/4W Resistor R4,R11__________1M 1/4W Resistors R7______________4K7 1/4W Resistor R8______________1K5 1/4W Resistor R10,R12-R14_____1K 1/4W Resistors C1,C4___________1µF 63V ...