The post explains a simple circuit that will enable car drivers to stop their car at an exact safe distance from the wall without the risks of colliding with the garage walls.
A new use of solar cells allows you to position your car in the garage way more easily than making use of old tires, a mirror, or a chalk mark etc.
How the Circuit Works
There are six solar cells shown is figure below. Those cells serve not only power supply but also as proximity sensor. They are commercially available in comparatively lesser price.
The voltage is developed in potentiometer P1. The voltage is mainly dependent on the brightness of light falling onto the solar cells.
The garage stop light circuit gets actuated as soon as the main beam of one of the headlight of the car falls directly onto the solar cells from a distance nearly of 200 mm or 8 inches. The distance can differ slightly with P1.
Under those circumstances, the voltage developed across C1 is nearly 3V. The voltage is enough to trigger the N1 relaxation oscillator.
The BC547B is then turned on via buffer N2, so that D3 starts to flash the light. Diodes D1 and D2 gives an extra rise in the threshold limit of the circuit. The total voltage decrease of 1.2 V across them ensures at pin 1 of the 4093, every time 1.2 V below the voltage developed by those cells.
As the trip level of N1 remains nearly about 50% of the supply voltage, the oscillator will only start working when the supply voltage is more than 2.4 V.
The circuits, including the solar cells can be best developed on a small veroboard.
The stop light circuit is then fitted in a translucent or transparent fibre case which is man-made. On the garage wall the case is being fitted in such a way so that the beams from the car’s headlight shine directly onto it. This is shown in the following figure.
On the same wall, the LED is fitted, but a little higher so that the driver can easily see this. When entering the garage, the driver must switch on the main beam of the car’s headlight.