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#Post#: 33--------------------------------------------------
LDR Connection
DIR By: Dioni
Date: August 13, 2016, 12:47 am
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Please state your reason why.
#Post#: 38--------------------------------------------------
Re: LDR Connection
DIR By: cefresto
Date: August 13, 2016, 3:03 am
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The base of the transistor acts as the "gate" where the
electrical supply enters and the one who is the lead responsible
for activating the transistor. And because of that the LDR
should be connected to it.
For example, we are using NPN transistor and we connected the
LDR to its base, when it’s light, the LDR has low resistance.
This makes the voltage at the base of the transistor higher.
High enough to turn the transistor ON. Because the transistor is
turned on, current flows through the transistor. It flows from
the positive battery terminal, through R1, the LED, and the
transistor down to the negative battery terminal. This makes the
LED light up. And when its dark, the oppposite happens.
HTML http://www.build-electronic-circuits.com/ldr-circuit-diagram/
:)))
#Post#: 41--------------------------------------------------
Re: LDR Connection
DIR By: Junaimah
Date: August 13, 2016, 10:49 am
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In creating our circuit the base part of the transistor are we
usually connect to the LDR. Because base part of the transistor
is the gate controller device for the larger elecrical supply.
By sending varying levels of current from the base, the amount
of current flowing through the gate from the collector may be
regulated.
#Post#: 52--------------------------------------------------
Re: LDR Connection
DIR By: butihenmy
Date: August 14, 2016, 4:29 am
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In creating a circuit the base part of the transistor is
connected to the LDR. Where the base of the transistor is act as
a gate gate controlle r device. This example is what i've read
on some sites. When it’s dark, the LDR has high resistance. This
makes the voltage at the base of the transistor too low to turn
the transistor ON. Therefore, no current will go from the
collector to the emitter of the transistor. All the current will
instead pass through the LDR and the potentiometer. When it’s
light, the LDR has low resistance. This makes the voltage at the
base of the transistor higher. High enough to turn the
transistor ON. Because the transistor is turned on, current
flows through the transistor. It flows from the positive battery
terminal, through R1, the LED, and the transistor down to the
negative battery terminal. :) :) :)
#Post#: 61--------------------------------------------------
Re: LDR Connection
DIR By: cha sarmiento
Date: August 14, 2016, 10:34 am
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Weusually connect the LDR to the base part of the transistor
because mostly in the way of constructing a circuit that turns
on the LED when it goes dark. In the LDR and the other Resistor
form a simple 'Potential Divider' circuit, where the centre
point of the Potential Divider is fed to the Base of the NPN
Transistor.
#Post#: 66--------------------------------------------------
Re: LDR Connection
DIR By: darlyn
Date: August 14, 2016, 12:09 pm
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Mostly, we connect the LDR of the BASE part of the transistor.
#Post#: 83--------------------------------------------------
Re: LDR Connection
DIR By: justine
Date: August 14, 2016, 9:44 pm
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We usually connect the LDR to the Base of the resistor.
It is said that when the light level is low the resistance of
the LDR is high. This prevents current from flowing to the BASE
of the transistors. Consequently the LED does not light. ;D
#Post#: 87--------------------------------------------------
Re: LDR Connection
DIR By: Kayla Jem Juliano
Date: August 14, 2016, 9:51 pm
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We usually connect the LDR to the base part of the resistor.
Because the LDR has high resistance. This makes the voltage at
the base of the transistor too low to turn the transistor ON.
:)
#Post#: 91--------------------------------------------------
Re: LDR Connection
DIR By: jaylenebarias
Date: August 14, 2016, 10:00 pm
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This LDR circuit diagram shows how you can make a light
detector. An LDR or “Light Dependent Resistor” is a resistor
where the resistance decreases with the strength of the light.
Light Dependent Resistors (LDR) are also called photoresistors.
They are made of high resistance semiconductor material. When
light hits the device, the photons give electrons energy. This
makes them jump into the conductive band and thereby conduct
electricity.
When it’s dark, the LDR has high resistance. This makes the
voltage at the base of the transistor too low to turn the
transistor ON.
Therefore, no current will go from the collector to the emitter
of the transistor. All the current will instead pass through the
LDR and the potentiometer.
When it’s light, the LDR has low resistance. This makes the
voltage at the base of the transistor higher. High enough to
turn the transistor ON.
Because the transistor is turned on, current flows through the
transistor. It flows from the positive battery terminal, through
R1, the LED, and the transistor down to the negative battery
terminal.
This makes the LED light up.
The Components Used In The Light Detector Circuit
The resistor R1 controls the amount of current going through the
LED. It’s simple to calculate. I have written an article on how
to calculate the resistor value for an LED.
If you are using an LED with 2V voltage drop, you will have a 7V
voltage drop over the resistor when the transistor is ON. By
using Ohm’s law we can find the current:
I = \frac{U}{R} = \frac{7V}{390 \Omega} = 18 mA
And 18 mA is usually a good current value for common LEDs.
What if you want to power the circuit with something other than
a 9V battery? Then you need to change the resistor value to get
the right amount of current flowing through the LED.
The variable resistor R2 is used to change the trigger point for
the LED. That is, how much light that is needed for the LED to
turn ON and OFF.
You can probably get away with a 10k potentiometer. It depends
on the resistance of your LDR. But with a 100k potentiometer you
will have room for a wider range of LDR values
Making The LED Turn ON When it’s Dark
You can also make the LED turn ON when it is dark instead of
when it is light.
replace the NPN transistor with a PNP transistor
#Post#: 100--------------------------------------------------
Re: LDR Connection
DIR By: carrenjoy
Date: August 15, 2016, 8:26 am
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When it’s dark, the LDR has high resistance. This makes the
voltage at the base of the transistor too low to turn the
transistor ON.
Therefore, no current will go from the collector to the emitter
of the transistor. All the current will instead pass through the
LDR and the potentiometerWhen it’s light, the LDR has low
resistance. This makes the voltage at the base of the transistor
higher. High enough to turn the transistor ON.
Because the transistor is turned on, current flows through the
transistor. It flows from the positive battery terminal, through
R1, the LED, and the transistor down to the negative battery
terminal.
And also,
Transistors can be regarded as a type of switch, as can many
electronic components. They are used in a variety of circuits
and you will find that it is rare that a circuit built in a
school Technology Department does not contain at least one
transistor. They are central to electronics and there are two
main types; NPN and PNP. Most circuits tend to use NPN. There
are hundreds of transistors which work at different voltages but
all of them fall into these two categories.
TWO EXAMPLES OF DIFFERENT SHAPES OF TRANSISTOR
Transistors are manufactured in different shapes but they have
three leads (legs).
The BASE - which is the lead responsible for activating the
transistor.
The COLLECTOR - which is the positive lead.
The EMITTER - which is the negative lead.
The diagram below shows the symbol of an NPN transistor. They
are not always set out as shown in the diagrams to the left and
right, although the ‘tab’ on the type shown to the left is
usually next to the ‘emitter’
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