This is the basic dark and light sensor which using photoresistor as sensing component.

The transistor act like as a switch, when the “switch” in on condition then the relay will be activated.

This is the color sensor circuit diagram. This circuit will sense eight colors that are: , green, red and blue (as primary colours); magenta, cyan and yellow (as secondary colours); and black and white. It’s will be very useful for robotics project.

The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered.

Turn on and turn off your electrical devices using touch switch, so you can “play” your electronic devices more fun.. . Touch switch don’t need mechanical part, so they will not worn out due to mechanical contact. Touch switches can be used in places where regular switches would not last, such as wet or very dusty areas. You just need to add some relay to switch your devices which require high voltage supply.

Here the schematic diagram:

Component part list:

Part      Total Qty.    Description

C1         1          10uF 16V     Electrolytic Capacitor
R1, R2     2          100K 1/4 Watt Resistor
R3         1          10 Meg 1/4 Watt Resistor
U1         1          4011 CMOS NAND Gate IC
MISC       1          Board, Wire, Socket For U1

This is a simple fire alarm circuit based NE555 timer and use thermistor as temperature sensor. This sensor will activate the transistor when the temperature is in high value.

The thermistor offers a low resistance at high temperature and high resistance at low imperature. This phenomenon is employed here for sensing the fire.

The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2.

This is alternate wireless switching using ultrasonic sensor. The distance of switching range should be more than 10 meters.

Please visit this page for more explanation.