“Hee Haw” Siren Circuit

The “Hee Haw” Siren Circuit is a fun sound project that makes a high and low noise like “Hee Haw” instead of one long sound.

It is made using simple electronic parts like resistors, capacitors and transistors or sometimes ICs.

The pitch of the sound goes up and down again and again.

We can find it in toys, alarms or fun DIY projects.

It sounds like a cartoon siren and gets its name because it sounds like someone saying “Hee Haw” like a funny donkey noise.

Circuit Working:

Parts List:

This circuit uses two astable multivibrators also called oscillators that create signals without needing outside input.

One oscillator runs slower and controls the faster one and this changes in speed that creates the “Hee Haw” sound.

How it works:

The first part uses two BC547 transistors Q1 and Q2, two 100uF capacitors C1 and C2, three resistors 3.9k, 5.6k and 220Ω, and an LED.

Capacitor C1 sets the speed of this low-frequency oscillator.

When Q1 turns ON it charges C1 through the 5.6k resistor.

As C1 charges the Q1 turns OFF and Q2 turns ON.

C1 then discharges through the 220Ω resistor and LED, by making the LED blink.

This cycle keeps repeating, creating a slow flashing signal.

The second part uses two more BC547 transistors Q3 and Q4, two 100nF capacitors C3 and C4, and two 220Ω resistors.

This part runs faster and creates the siren sound.

The slow oscillator controls Q3 which changes the sound frequency.

A speaker is connected to Q4 through an 8Ω resistor.

The changing voltage at Q4 makes the “Hee Haw” sound.

We can change how the siren sounds by using different capacitor or resistor values.

Even though the circuit is simple, always be careful with electronics.

Use a proper power supply and avoid electric shock.

If anyone is unsure then ask someone who is experienced to help.

Formulas:

The frequency and timing of an astable multivibrator can be calculated using formulas.

Main Formulas:

1. Frequency (f):

f =1​ / T

where,

• T is the total time of one full cycle.

2. Time Periods T1 and T2:

T1 = 0.693 × (R1 + R2) × C

Time capacitor charges through R1 and R2

T2 = 0.693 × R2 × C

Time capacitor discharges through R2

3. Total Time (T):

T=T1+T2

This is the total period of the oscillation.

4. Duty Cycle (D):

D = T1 / T

This shows the ratio of ON time T1 to the full period.

These formulas are used when building the multivibrator using basic parts like transistors, resistors and capacitors.

Keep in mind the real circuit values and design can affect the exact frequency and duty cycle and these formulas give us a good starting point.

How to Build:

To build a “Hee Haw” Siren Circuit follow the below mentioned connections steps:

Q1 Transistor Connection:

• Connect the collector to the positive side using LED1 and a 220Ω resistor.
• Connect the base to the end side of the 5.6k resistor.
• Connect the emitter to ground.

Q2 Transistor Connection:

• Connect the collector to the positive side using LED2 and a 220Ω resistor.
• Connect the base to the starting side of the 5.6k resistor.
• Connect the emitter to ground.

Q3 Transistor Connection:

• Connect the collector to a 3.9k resistor.
• Connect the base to the end side of a 100k resistor.
• Connect the emitter to ground.

Q4 Transistor Connection:

• Connect the collector to the other side of the 3.9k resistor.
• Connect the base to the starting side of the 100k resistor.
• Connect the emitter to ground.

Q5 Transistor Connection:

• Connect the collector to ground.
• Connect the base between Q4s collector and the 3.9k resistor.
• Connect the emitter to one end of the speaker.

Safety Tip:

• This circuit uses low voltage but still we need be careful.
• Check all connections before turning it on.
• Use a power supply with the right voltage.

Conclusion:

The “Hee Haw” Siren Circuit is a fun project that makes a two-tone sound like a funny siren.

It works using oscillators that control the sound.

It is not for real emergencies, but it is a great way to learn electronics and have fun.

Always stay safe when working with circuits.

References:

Hee Haw