This circuit explains a special type of volume control for electronics that uses digital parts instead of a knob.
Regular volume knobs use resistors to control the loudness, but this type uses tiny computer chips to do the same thing.
This can be more precise and offer other features.
Circuit Operation:
Parts List:
| Category | Type | Quantity |
|---|---|---|
| Resistors | ||
| R1, R2, R20, R32 22k | 1/4 watt | 4 |
| R3 18k, R4 15k, R5 10k, R6 8.2k, R7 5.6k, R8 4.7k, R9 1k, R10 300Ω | 1/4 watt | 1 each |
| R11 1Ω, R12 300Ω, R13 1k, R14 15k, R16 8.2k, R17 10k, R18 15k, R19 18k | 1/4 watt | 1 each |
| R21 47k | 1/4 watt | 1 |
| R22 to R31, R33 to R43 10k | 1/4 watt | 21 |
| Preset VR1 47k | 1 | |
| Capacitors | ||
| C2 0.1μF | Ceramic | 1 |
| C1 10μF 25V | Electrolytic | 1 |
| C3 to C12 1μF 25V | Electrolytic | 10 |
| Semiconductors | ||
| Red LED1 to LED10 | 5mm 20mA | 10 |
| Transistors | ||
| T1 to T10 | BC547 | 10 |
| IC1 555, IC2 4017 | 1 each | |
| S1 Push-to-on switch | 1 | |
| S2 1 pole 2-way switch | 1 |
This functionality is achieved through a combination of a decade counter IC 4017 and various transistors.
Input is applied at the collectors and the output is extracted from the emitters of the transistors.
Depending on the IC 4017 output the corresponding transistor becomes saturated.
The emitter output, passed through a coupling capacitor to eliminate DC components, allows the signal to reach the amplifier.
When pin 4 of IC 4017 goes high, the associated transistor T2 saturates enabling the direct transmission of the input signal to the output via the collector resistance.
Initiate the process by pressing switch S1.
The timer IC 555 generates pulses at regular intervals, feeding them to IC2.
The transistor selection depends on the output of IC 4017.
Once the desired volume is achieved release the switch.
To reset the counter switch S2 is positioned at A.
The time period of the output pulses can be adjusted using the following formula:
Formula:
The below mentioned formula explains a circuits time constant Td, which is probably utilized in a timer circuit:
Td = 0.693(R1 + 2√R1 + 2R3²) C1 seconds
here,
- Td: This is the circuits time constant expressed in seconds.
- It is the amount of time that, when connected to a voltage source via a resistor, the voltage across a capacitor C1 charges to around 63.2% (1 – 1/e) of its ultimate value.
- 0.693: Based on the mathematical characteristics of capacitors charging over time, this constant value was determined.
- R1: This represents the resistance of resistor R1 in ohms.
- √R1: This represents the square root of resistor R1.
- 2R3²: This is equivalent to resistor R3 multiplied by itself twice, or two times the square of its resistance.
- C1: This represents the capacitance of capacitor C1 in farads.
How formula functions:
In essence, the formula determines how long it will take the circuits capacitor C1 to charge.
The charging speed is influenced by resistors R1 and R3.
This is a condensed explanation:
Greater Resistance R1 or R3: A higher resistance causes the capacitor to take longer to charge, which raises the time constant Td.
Greater Capacitance C1: A greater capacitor has a larger time constant because it can hold more charge and takes longer to reach its ultimate voltage.
How to Build:
Building the described circuit involves several components, including transistors, ICs, resistors, capacitors, and switches.
Schematic Design:
- Create a schematic diagram based on the provided information.
- Place components on a breadboard or design a PCB layout.
Connect ICs:
- Connect the IC 4017 and IC 555 to the appropriate power supply Vcc and GND.
- Connect pin 4 of IC 4017 to the transistor base or any other appropriate input.
Transistor Connections:
- Connect transistors T1, T2 to the circuit based on their roles in the switching mechanism.
Resistor Placement:
- Connect resistors R1, R2, R3 to the circuit according to their specified values.
Capacitor Connections:
- Connect capacitors C1, coupling capacitor to block DC components and ensure proper signal transmission.
Switch Wiring:
- Connect switches S1, S2 to control the circuit’s operation with S1 initiating the process and S2 resetting the counter.
Preamplifier and Amplifier:
- Connect the preamplifier output and amplifier input appropriately.
Power Supply:
- Provide the necessary power supply voltage Vcc to the circuit.
- Carefully inspect the connections.
- Power up the circuit and test its functionality.
- Use an oscilloscope or other measuring tools to ensure the desired behavior.
Adjustments:
- Fine tune the circuit, if necessary based on the desired volume control and switching actions.
Caution:
It is important to refer to the datasheets of the specific components you are using and double check the connections to avoid any mistakes.
If you are not experienced with electronics consider seeking assistance from someone with expertise or consulting with professionals in the field.
Conclusion:
Digital volume controllers offer advantages such as precise control, remote operation, and the ability to integrate with digital audio processing systems.
They are commonly used in audio amplifiers, home theater systems, multimedia speakers, and other audio equipment where digital control and automation are desired.