A controller is required to monitor the natural illumination of a sports stadium and, when the ambient light is below a pre-set level, to switch on external lighting.
The system is required to be of high integrity, and various monitoring indicators are to be incorporated as specified below. Furthermore, the status of the light (Large white LED) is to be monitored, and if this should fail, when the lighting should in fact be on, a warning signal is to be given in the form of a flashing orange LED.
Circuit Requirements
1. A light dependent resistor (LDR) is to be used to determine ambient light levels.
2. A red light emitting diode (LED) should illuminate whenever the ambient light level is below the pre-set value.
3. A green LED should be illuminated if the ambient light is above the predetermined level. Note, the use of two LEDs in this manner serves to indicate that power is applied to the system, as one LED will always be on.
4. An orange LED is to flash on and off repeatedly, in the case that the ambient light level is low, and the white LED is not illuminated, i.e., it has failed.
5. Individual functional blocks of the circuit should be constructed and operation verified on breadboard. One example of such a component block may be the LDR and comparator light detection circuit.
Circuit Design Suggestions The following points are suggestions as to the circuitry you might choose to use, and are based on the material covered in recent lectorials and introductory practicals which assumes a knowledge of operational amplifiers, NAND gates, light dependent resistors (LDR), 555 timer and transistors. However, other circuitry may be used, but you should discuss this with the class tutors and/or technicians before
implementation.
1. A single 12-volt power supply may be employed.
2. The circuit may be built in a logical form, that is, one functional block at a time, in order that each stage may be built and tested before the following block is constructed.
3. An operational amplifier may be used as a comparator to “digitise” the voltage across the LDR light sensor.
4. A transistor may be used to switch power to the large white LED.
5. The voltage across the LDR may be monitored by an operational amplifier configured as a comparator.
6. A NAND gate may be used to gate the “white LED” signal with the ambient light status.
7. A NAND gate or a 555 timer may form the basis of the oscillator required to drive the orange LED.
here is my ATTEMPT
