Elenco Projects 102-305 - Manual (Page 58)

-57-
Project #261
OBJECTIVE: To build a motion detector that senses an objects
movement.
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.
Motion Detector (II)
Project #259
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 #260
Sound Pulse Oscillator
OBJECTIVE: To build a 0.5Hz - 30Hz oscillator and hear it on a speaker.
Use the circuit from project #259.
Connect a single snap under the speaker (SP) and then connect it across the LED (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.
To learn more about how circuits work, visit www.snapcircuits.net or page 74 to find out about our Student Guides.