Elenco Electronics 202 - Manual (Page 88)

-87-
Project #204
OBJECTIVE: To build a motion detector that senses an objects
movement.
Motion Detector (II)
Project #202
Oscillator 0.5 - 30Hz
OBJECTIVE: To build a 0.5Hz - 30Hz oscillator that will light an LED.
Set the adjustable resistor (RV) to the bottom position and then turn the slide
switch (S1) on. The LED (D1) will start flashing at a frequency of 0.5Hz (once
every two seconds). Slowly adjust the adjustable resistor and the LED flashes
faster. As the frequency increases, the LED flashes faster. Eventually, the LED
flashes so fast, it looks like it is on all of the time.
Project #203
Sound-pulse Oscillator
OBJECTIVE: To build a 0.5Hz - 30Hz oscillator and hear it on a speaker.
Use the circuit from project #202. Connect a single snap under the speaker (SP)
and then connect it across the LED (D1) (on level 4). Turn the slide switch (S1)
on and now you can hear the oscillator. Adjust the adjustable resistor (RV) to hear
the different frequencies. Now you can hear and see the frequencies. Note: You
may not hear sounds at all settings of the adjustable resistor.
Turn the slide switch (S1) on and move the adjustable resistor (RV)
control all the way up. The brightness of the LED (D1) is at maximum.
Now, move the adjustable resistor control down until the LED goes out.
Set the control up a little and the LED lights dimly.
Move your hand from side to side over the photoresistor (RP). As your
hand blocks the light, the LED goes out.
The amount of light changes the resistance of the photoresistor and the
current flow to the base of the NPN transistor (Q2). The transistor acts
like a switch. Its base current is supplied through the photoresistor. As
the base current changes, so does the current flow through the LED.
With no base current, the LED goes out.