This is a simple train whistle circuit. We have many ways to generate a two-tone sound circuit. I love to collect a basic or small circuit.
This circuit may be useful for you. When we press SW1, the speaker will emit the sound like a train whistle. It is suitable for sound alarms and other.
The main component of this circuit is NE556, a great integrated circuit.
This advantage of this circuit is small and cheap. Because it uses a single IC. Working out sound speakers directly.
How this circuit works
When we take the 9v power supply(9V battery) to the circuit. It will start to generate low frequency out of pin 5. A separate section to the pin 9 to the speaker driver. This Frequency depends on the R2 and C2.
The signal from the pin 5 comes to pin 8. And there is R6 and C1 to reset with a delay circuit.
When it is reset, pin 8 gets the signal and this circuit will generate a high frequency signal comes out of pin 9 of IC1. Which there is R3, R4, C5 to set this signal.
Thus, the characteristic of the sound is to start the high-frequency sound. Then change to low frequency.
Parts you will need
IC1—NE556 Dual Precision Timer; Quantity:1
D1,D2—1N4001 1A, 50V Diodes; Quantity:2
C3—0.1uF 50V; Quantity:1
C5—0.047uF 50V; Quantity:1
C1—4.7uF 50V; Quantity:1
C2—2.2uF 50V; Quantity:1
C4—220uF 16V; Quantity:1
—0.25W Resistors, tolerance: 5%
SP1—8 ohms speaker
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