Roadway lighting systems are now widely accepted as essential for controlling traffic flow in a wide number of applications. 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.
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 Road Stud Circuit Schematic
- 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.
Fabrication of L (the toroid core transformer)
- Take one piece of 30 SWG enamelled copper wire
- Start off by sticking the wire through the middle of the small toroid core
- Wrap the wire around the toroid to make 20 turns
- Repeat the process with the second piece of 30 SWG enamelled copper wire
- Now join the two coils (windings) of the toroid. For this Take one end of the first coil on the one side of the toroid and , one end of the second coil on the other side of the toroid. Now connect them together. These two wires forms the centre pole of the toroid as in the circuit diagram which is connected to the positive terminal of the battery (Note the two black dots next to the toroid windings in the circuit diagram. These two dots indicate the polarity and as you can see the two windings are opposite to each other. Make sure this polarity is in right order).
Please note: The prototype is suitable for lab evaluation/demonstration puproses only. The “real” stud should be fixed to the road in a conventional way, it must be highly visible in all lighting and roadway conditions.To achieve the maximum possible driver acceptability it may necessary to put all the circuitry in the same housing as that now used for conventional reflector studs. It is recommended to use materials like Die Cast Aluminium and High Strength Polycarbonate for making a suitable enclosures. An artistic view is included here (see figure below)!
- Current consumption in idle state (day time – Solar panel working/LEDs OFF ): near 1 mA /from 1.2V battery
- Current consumption in active state (night time – Solar panel not working/LEDs ON ): near 30 mA /from 1.2V battery
- Fabrication of an SMD PCB version is under consideration!
Check our the solar projects category for more related circuits!