Solar cat eye road stud are widely used to assist controlling traffic flow and roadway security. In practice, such systems operate well above the road surface and use a number of well known and widely accepted colours, with lights in particular orientations to make the message to a driver clear and univocal thereby improving the outturn of the road while enhancing safety aspects. A solar cat eye road stud is nothing but an “Active Road Stud” with automatic switching function, realized using the combination of a small solar panel, re-chargeable cell, and LED driver circuitry. To make a solar cat eye road stud in Lab, following materials are needed. Solar Panel: A 3V/100 mA (0.3W) rated solar panel is used here. Such panels are widely available at a cost less than $2. Output of the solar panel (SP1) is directly connected to the re-chargeable cell (B1) through an ordinary silicon diode 1N4007 (D1).
Re-chargeable Battery: The power back-up mechanism is realized using a single 1.2V/820 mAh Ni-Mh battery (B1) . For compactness, an AAA type is used here.
LED Driver Circuitry: This section is nothing, but a replica of the popular “JouleThief” circuit. Here the LED driver circuitry drives two 5mm Red LEDs (LED1&LED2) only during night time. For automatic switching operation, one BC547 transistor (T1) is wired with the joule-thief. Associated 4K7 Preset pot (P1) can be used to alter the sensitivity of this automatic switching (day/night detector) circuit.
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