Transcript PS 141 Presentation

PS 141 Presentation
By
Gabe, Tanya Mae
Kim, Jaeyoun
Ong, Raymond Carey
PROJECT PLAN
We want to build a light sensitive toy car.
Whenever it detects light, it will move
opposite of that direction in order to
avoid bumping the wall.
MATERIALS USED
Bread board
Light Dependent
Resistor
Diode
NE 555 Timer IC
Resistors
Transistors (2N2222,
2N2907)
SENSOR PART
We connected the LDR to the 555 IC to detect
the Logic ‘0’ and ‘1’. If the surrounding of the
LDR is dark, the resistance of the LDR goes very
high. So, the voltage of the LDR node becomes
lower than 1/3 of the voltage source. So, the
output will be Logic ‘1’. On the other hand, if the
surrounding is bright, the resistance of the LDR
becomes low, the voltage of the LDR node is
higher than 2/3 of the voltage source. That
makes the output (pin 3) of 555 IC to Logic ‘0’.
After that, we connected the pin 3 of 555 IC to
the motor part of our circuit
MOTOR PART
We connected the pin 3 of 555 IC of
the LDR part circuit to this motor
circuit.
DISCUSSION
LDR Part
First of all, we tested LDR
to see its characteristics on
how
it
changes
its
resistance. The resistance
of LDR varies according to
the amount of light that
falls on it. In darkness, its
resistance is much higher
than that of LDR in
brightness.
DISCUSSION
Transistor and Motor Part
We connected a transistor to control the motor. To activate the
transistor, we had to supply a minimum voltage to its base.
When a light falls on the LDR, the resistance of the LDR is
low so that the voltage on the base of the transistor is not
sufficient to drive it into conduction. When we darkened LDR,
the resistance of the LDR increased. So, the potential at the
base of the transistor was raised. The resulting increase in the
current flow at the base of the transistor amplified at the
collector of the transistor to turn the motor on. Moreover,
when the transistor is off, no current flows through the
transistor.
DISCUSSION


Inverter
To run the motor either
clockwise or counterclockwise,
we built the inverter circuit with
the transistor. So, the output of
the inverter is the opposite of
the input.
If the input is 5 volts (Logic 1),
the output will be 0 volts (Logic
0) so that the motor will run.
However, if the input is 0 volts,
the output will be 5 volts.
Therefore, the motor might not
run. We used several
transistors to control the
direction of the motor.
DISCUSSION
Diode
We connected the diode to the DC
motor to prevent the destruction of our
circuit due to the back voltage or
counter electromotive force (EMF).