Lanes on roads are traditionally marked in a passive way with reflecting road-studs and high visibility paint, often coupled with other reflectors on short posts at the sides of the highway. However, on busy roads with dipped headlights these “passive road studs” are harder to see, and the range of visibility is dramatically reduced,while in wet conditions they can become completely invisible. Recently some new “powered road-studs” (active road studs) have appeared as options for roadway designers, and a simple approach to the new trend is accounted here.

“Solar LED Road Marker” 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.

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.