Astable 555 Timer Projects

How it Works:

The Permanent Magnet DC Motor is the most commonly used type of small direct current motor available producing a continuous rotational speed that can be easily controlled. Small DC motors are ideal for use in applications where speed control is required such as in small toys, models, robots, and other such electronics circuits.

• A DC motor consists basically of two parts, the stationary body of the motor called the “Stator” and the inner part which rotates producing the movement called the “Rotor”. For D.C. machines the rotor is commonly termed the “Armature”.

• Generally in small light-duty DC motors, the stator consists of a pair of fixed permanent magnets producing a uniform and stationary magnetic flux inside the motor giving these types of motors their name of “permanent-magnet direct-current” (PMDC) motors.

• The motor's armature consists of individual electrical coils connected together in a circular configuration around its metallic body producing a North-Pole then a South-Pole then a North-Pole etc, type of field system configuration.

The current flowing within these rotor coils produces the necessary electromagnetic field. The circular magnetic field produced by the armature windings produces both north and south poles around the armature which are repelled or attracted by the stator’s permanent magnets producing a rotational movement around the motor central axis as shown. As the armature rotates electrical current is passed from the motor's terminals to the next set of armature windings via carbon brushes located around the commutator producing another magnetic field and each time the armature rotates a new set of armature windings are energized forcing the armature to rotate more and more and so on. So the rotational speed of a DC motor depends upon the interaction between two magnetic fields, one set up by the stator’s stationary permanent magnets and the other by the armature's rotating electromagnets, and by controlling this interaction we can control the speed of rotation. The magnetic field produced by the stator’s permanent magnets is fixed and therefore can not be changed but if we change the strength of the armatures electromagnetic field by controlling the current flowing through the windings more or less magnetic flux will be produced resulting in a stronger or weaker interaction and therefore a faster or slower speed.

So how do we control the flow of current through the motor? Well many people attempt to control the speed of a DC motor using a large variable resistor (Potentiometer.) While this may work, it generates a lot of heat and wasted power in the resistance. One simple and easy way to control the speed of a motor is to regulate the amount of voltage across its terminals and this can be achieved using “Pulse Width Modulation” or PWM.

Also, the amplitude of the motor voltage remains constant so the motor is always at full strength. The result is that the motor can be rotated much more slowly without it stalling. So how can we produce a pulse width modulation signal to control the motor? Easy, use an Astable 555 Oscillator circuit as shown above.

This simple circuit based around the familiar NE555 or 7555 timer chip is used to produce the required pulse width modulation signal at a fixed frequency output. The timing capacitor C is charged and discharged by current flowing through the timing networks RA and RB as we looked at in the 555 Timer tutorial.

The output signal at pin 3 of the 555 is equal to the supply voltage switching the transistors fully “ON”. The time taken for C to charge or discharge depends upon the values of RA, RB.

The capacitor charges up through the network RA but is diverted around the resistive network RB and through diode D1. As soon as the capacitor is charged, it is immediately discharged through diode D2 and network RB into pin 7. During the discharging process, the output at pin 3 is at 0 V and the transistor is switched “OFF”.

Then the time taken for capacitor, C to go through one complete charge-discharge cycle depends on the values of RA, RB, and C with the time T for one complete cycle being given as:

The Astable frequency is constant at about 256 Hz and the motor is switched “ON” and “OFF” at this rate. Resistor R1 plus the “top” part of the potentiometer, VR1 represents the resistive network of RA. While the “bottom” part of the potentiometer plus R2 represents the resistive network of RB above.

These values can be changed to suit different applications and DC motors but providing that the 555 Astable circuit runs fast enough at a few hundred Hertz minimum, there should be no jerkiness in the rotation of the motor.

Pulse width modulation is a great method of controlling the amount of power delivered to a load without dissipating any wasted power. The above circuit can also be used to control the speed of a fan or to dim the brightness of DC lamps or LEDs. If you need to control it, then use Pulse Width Modulation to do it. 

Questions:

1. What is PWM, and how does it differ from other methods of motor control?

2. How does varying the duty cycle of the PWM signal affect the motor speed?

3. How do you adjust the frequency and duty cycle of the PWM signal?

4. How does PWM contribute to the energy efficiency of the motor controller?

5. How is heat managed in the motor controller, especially during prolonged use? Are there any heat sinks or cooling mechanisms incorporated? When would you need them and how would you apply them?

6. In what practical scenarios or applications could this PWM motor controller be employed?

For more information on Integrated Circuits and the 555 Timer, check out our page on Integrated Circuits.

How it Works:

1. The conditions are met when a capacitor is alternating through charging and discharging cycles. When a capacitor is discharging into pins 6 and 2 it creates high signals for the logic gates within the 555 timer.

2. Those high signals combined with the input from the buttons will increase or decrease the amplitude of the squarewave output. 

3. As you work down the row of buttons, you increase the resistance of the circuit ending at pin 2/6 which lowers the amplitude of the square wave output. 

4. As the square wave amplitude is decreased, the pitch will become lower.

Questions:

1. What is the role of the piezo buzzer in sound production?

2. How are different musical notes achieved in the Piezo Piano?

3. Can you design a more sophisticated keyboard layout for a wider range of notes?

4. What calibration methods can be employed to enhance accuracy?

5. How might you incorporate additional features, such as volume control?

For more information on Integrated Circuits and the 555 Timer, check out our page on Integrated Circuits.

What to Expect:

As you spin POT1, you will change the pitch that the speaker plays. See Piezo Piano above for a more detailed explanation of how resistance and capacitance change the frequency of the 555 duty cycle heard as pitch. 

How it Works:

The Otamatone's unique sound production, facilitated by a Voltage-Controlled Oscillator (VCO) powered by a 555 timer, operates on a straightforward principle. 

1. The 555 timer is configured as a VCO, generating square waves with a frequency determined by the voltage applied to its control pin. In the Otamatone, the potentiometer acts as the voltage input source. As the player manipulates the potentiometer, the varying voltage levels modulate the pitch of the generated sound.

2. When the player rotates the potentiometer, it alters the resistance and, consequently, the voltage reaching the control pin of the 555 timer. This manipulation results in a dynamic change in the frequency of the square waves produced by the VCO. The pitch of the sound corresponds to these variations, allowing the player to create a range of tones and melodies.

3. For more volume, omit POT2 and connect the speaker to ground through a .1uF capacitor

Questions:

1. Why use a speaker compared to a buzzer like the Piezo Piano above?

2. What calibration methods can be employed to enhance accuracy?

3. How might you incorporate additional features, such as volume control?

4. What role does the 555 timer play in the sound production?

5. How can the design of the Otamatone be modified for different aesthetic or functional purposes?

6. Are there alternative components or configurations that can be explored?

For more information on Integrated Circuits and the 555 Timer, check out our page on Integrated Circuits.

How it Works:

1. Inductors are nothing but coils of enameled copper wire that come in different shapes and sizes. Based on various parameters the inductance of an inductor is calculated.

2. In the schematic above, the circuit has an air-cored inductor. They are coils left in the air with nothing in or around them. A medium flow of magnetic field is generated by an air-cored inductor. These inductors have inductances of very little value.

3. When an inductor coil is wound on a core or moved near an object that has a ferrite or an iron core the inductance of the coil increases enormously. This value is much more than the air-cored one of the same size and shape

4. As you increase the inductance on the coil, the resistance it has also increases. This circuit ending at pin 2/6 raises the frequency of the square wave output when the resistance is decreased.

5. As the square wave amplitude is decreased, the pitch will become lower indicating that you have struck gold!

See our page on Magnetism for more details on Electro-Magnetism. 

Questions:

1. How does the metal detector function at a basic level?

2. What components are essential for its operation?

3. How can the sensitivity of the metal detector be adjusted?

4. What considerations are taken into account in choosing the size and shape of the coil?

5. How does the detector differentiate between various types of metals?

6. In a more advanced metal detector, what measures are taken to reduce false alarms?