Night Light Circuit Components Flashcards
What is an LDR’s maximum resistance?
About 1M ohms
What is a Light Dependant Resistor or LDR (Sometimes simply called a light sensor)?
An input component which converts brightness (light) to resistance. Made from cadmium sulphide (CDS) and the resistance decreases as the brightness of the light falling on the LDR increases.
What is an LDR’s minimum resistance?
About 100 ohms.
What is a Transistor?
It behaves like an electronic switch. It is a control component. It has three legs; the BASE, COLLECTOR and EMITTER.
Explain about fitting the Light Emitting Diode (LED)
It must be connected the right way round. A diagram of it may be labelled A or + for Anode and K or - for Cathode. The cathode is the short lead and there may be a slight flat on the body of round LEDs. Inside an LED the cathode is the larger electrode.
How can an LED be damaged during soldering?
If too much heat is conducted from the soldering iron, but this won’t happen unless you are very slow.
What colours are LEDs available in?
Red, orange, amber, yellow, green, blue and white.
Which colours of LED are the most expensive?
Blue and white
What changes the colour of LEDs?
The semiconductor material and not the adding body around the LED.
What are the 7 components in the night light circuit?
The LED, 9V battery, variable resister, LDR, 330 ohm resistor, 1K ohm resistor and the transistor.
What is the role of the variable resistor?
To make the circuit sensitive to a particular level of light.
How does the circuit work?
A low light level is sensed by the LDR. The LDR sends a signal to the transistor to indicate that light level is low and it responds by switching on the LED.
How do you prepare before soldering?
Moisten the sponge and heat up the soldering iron.
How do make a soldered joint?
Place the soldering iron on the wire and hold it over the joint’s loose end then cut the excess joint.
How do you check the soldered joint?
Try it with the battery or test to see if it’s loose
