Elenco Basic Electronic Experiments - Manual (Page 58)

58
EXPERIMENT #41: NOISY BLINKER
This circuit is similar to the last one. Connect the circuit (noting that the transistor bases are not connected although their
wires cross in the schematic). Press the switch and hold it down. The LED lights and you hear sound from the speaker.
Turn the knob on the variable resistor and the frequency of the sound changes. Can you tell what the LED is really doing?
It is actually blinking about 500 times a second, but to your eyes it appears as a blur or just dim. (This is why we told you
not to replace the large capacitors with small ones like these in the last experiment).
You can experiment with changing component values if you like. The 470
Ω resistor limits the sound loudness, replace it
with a wire to make the sound louder and replace it with a 10k
Ω to make the sound softer. Swapping the two capacitors
in the circuit will make the sound frequency higher, replacing them with the 10
μF or 100μF will make the frequency much
lower. You can also change some of the other resistors.
+9V
100k
Ω 1k
Ω
3.3k
Ω
470
Ω
S
P
473
502
.005 μF