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23.4 Circuit Explanation
To understand this circuit, let’s partition it in two parts, the first one is in the green square, and
the second one is in the blue square.
We used NE555(2) to generate high frequency, but it will not work until TR1 gets in the
saturation mode, the base of TR1 is connected to the output of NE555(1).
The first part is a delay circuit, when you press on the push button you are activating TR3, so
you will connect pic 2 to GND, therefore the output will be high, until C3 gets fully charged the
output will turn OFF.
Indeed you get two different frequencies on the output of NE555(2), the first one when you click
on the push button, you are activating NE555(1) therefore NE555(2), and connecting pin 5 of
NE555(2) to 5V through TR2, so we get a different frequency, but when you release the push
button, it will continue in the other frequency, so you will get two different sounds.
23.5 Example Picture
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