Elenco Projects 306-511 - Manual (Page 32)

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Project #384
OBJECTIVE: To build a circuit that lights an LED to indicate
the recording mode.
Recording LED
Indicator
Project #385
OBJECTIVE: To add a volt meter to the playback and record
circuit.
When recording, if the input signal into the microphone (X1) is too
high, distortion can occur. To monitor the level, a meter (M2) is placed
in series with the microphone.
Set the meter to the LOW (or 10mA) scale. Turn on the slide switch
(S1) and the meter defects to the right. As you speak into the
microphone, the meter indicates the change in current. Turn the switch
off and then on to record again, but this time speak louder. You will find
that the louder you speak, the more the meter deflects. The lamp (L2)
is used to limit current and will not light.
Playback & Record
with Meter
The circuit uses sound (beep) and light (LED) to indicate that you are
recording. Build the circuit; the red (D1) and green (D2) LED’s should
light. Now turn on the slide switch (S1). You hear one beep and the
green LED turns off. Speak into the microphone (X1) to record a
message. When you turn off the slide switch, or the circuit beeps twice
(indicating the recording is finished), the green LED turns on again.
Make sure that the slide switch is turned off. Press the press switch to
hear your recording followed by a song. The lamp (L2) is used to limit
current and will not light.