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KNS130
Complete all wiring connections as indicated in the sequence. Switch on the main switch. The motor will
spin. If you reverse the connection polarity of the diode by changing the wiring connection a bit, 17
connect to 44 and 2 connect to 45, then this time you will find that the circuit does not work. This is
because the diode does not allow current to follow through it in a reverse direction. Therefore the circuit
does not work this time.
12.18 A simple demonstration of the light sensor
Wiring Sequence
4-14, 13-49, 48-17, 18-3
18
17
4
3
14
13
49
48
Complete all wiring connections as indicated in the sequence. Switch on the main switch. You may notice
that the LED lights up very dimly. This indicates only a very small amount of current is flowing through it.
It depends on the intensity of light falling onto the light sensor. If you perform this experiment in a
darker place, the LED may not light up at all. If you use a torch to shine on the light sensor, you can see
that the LED light up brightly. This is because when there is more light, more current will be able to pass
through the light sensor and light up the LED.
12.19 A practical example: Light triggered LED
Wiring Sequence
4-23, 22-14, 24-49, 48-13-17, 18-3
14
13
22
4
3
18
17
24
23
48
49
Complete all wiring connections as indicated in the sequence. Switch on the main switch. This time, even
with a small amount of light, the LED will light up brightly! It is because in this circuit, the PNP transistor
is the real gateway to the LED, and the light sensor is only acting as a switch for opening the gateway!
When the upper part of the circuit is not connected, no current is flowing through the "Emitter" to the
"Base" of the transistor. So the gateway of the "Emitter" to the "Collector" is shut. When light falls on the
light sensor, the upper circuit is connected; a very small amount of current passes through the "Emitter"
to the "Base", and then the gateway of the "Emitter" to the "Collector" is opened! Electric current from
the battery can then flow through the transistor to the LED, and therefore the LED will light up brightly!
This circuit makes the light sensor to become a sensitive switch to detect light.
V. 01 – 01/02/2024
18
©Velleman nv
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