Matt circuit

This is basically a Schmitt Trigger circuit which receives input from a cadmium sulfide photo cell and controls a relay that can be used to switch off and on a street lamp at dawn and dusk. I have built the circuit with a 120 ohm/12 volt relay and monitored performance using a lamp dimmer, but did not connect the relay to an outside light. The photo cell should be shielded from the lamp to prevent feedback and is usually mounted above the light on top of a reflector and pointed upward at the sky so the lamp light does not strike the photo cell and switch off the lamp. Photo Electric Street Light Circuit Diagram The photo cell is wired in series with a potentiometer so the voltage at the junction (and base of transistor) can be adjusted to about half the supply, at the desired ambient light level. The two PNP transistors are connected with a common emitter resistor for positive feedback so as one transistor turns on, the other will turn off, and visa versa. Under dark conditions, the ph...

Most PN-junction diodes can be used as photodiodes. While not optimized for this application, they do work. When the diode is reverse biased, it will produce a small photovoltaic output as the light level is increased. LEDs are particularly suited for this task because their housings are transparent. You can construct a simple circuit that will assess the condition of ambient lighting and, because many LEDs’ packages are tinted to enhance their emitted color, may even yield a reasonable evaluation of the detected color. The results are not as effective as those obtained using a high-quality optical filter, which typically has narrow bandpass characteristics, but they can be quite acceptable. Though the design described here does not produce the accuracy of designs with laboratory-grade photodetectors and transimpedance amplifiers, it can be quickly assembled and will produce usable results at a low cost. Three LEDs are used; experimentation will indicate which device has the best sensi...