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 PartWe 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

DiodeWe connected the diode to the DC motor to prevent the destruction of our circuit due to the back voltage or counter electromotive force (EMF).