Understanding the characteristics of digital electronics
In our previous articles, we discussed the mechanisms of a voltage amplifier and analogue signals in general. Now, in this article, we’re going to switch focus a little and look at digital electronics.
The binary number system (Base2)
Before we look at digital electronics, we need to understand the binary number system. A computer can only understand the “on” and “off” states of a switch. These two states are represented by 1 and 0, and the combination of these form binary numbers. These numbers represent data, and as there are two digits used, it’s called a binary or base 2 system.
The binary system works under similar principles to the decimal system. However, it operates in base 2 rather than base 10. In other words, instead of columns being:
102|101|100
they are:
22 | 21 | 20
Instead of using the digits 0–9 we only use 0-1. Any number larger needs to go into the next column; for example, with 3 we need more than one column. The first column we fill is the right-most column, which is 20, or 1. Since 3 > 1, we need to use an extra column to the left. 3 is written as “11” in binary (1×21) + (1×20).
We can carry out the same mathematical calculations in binary that we do with decimal. We can carry out adding, subtracting, multiplication and division. We also can convert between binary and decimal. These calculations would be a whole article on their own, so we won’t go into that here.
Representation of a binary number
The table below shows a representation of binary numbers. LSB means left most bit, as binary represents data in numbers of bits. MSB means the right most bit.
| MSB | Binary Digit | LSB | ||||||
| 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 |
| 256 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
The first digit has a weight of 1 ( 20 ), the second digit has a weight of 2 ( 21 ), the third a weight of 4 ( 22 ), the fourth a weight of 8 ( 23 ) and so on.
Input and output devices
In order for an electronic circuit to perform any useful task or function, it needs to be able to communicate with the “real world,” whether this is by reading an input signal from an “ON/OFF” switch or by activating an output device to illuminate a light.
An Electronic System or circuit must be able or capable to “do” something and Sensors and Transducers are the perfect components for doing this. The word “Transducer” is the term used for both Sensors, which can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, and more, and Actuators, which can be used to switch voltages or currents.
The type of input or output transducer being used depends on the type of signal or process being “Sensed” or “Controlled,” but sensors and transducers are devices that convert one physical quantity into another.
Electrical Transducers
Devices which perform an “Input” function are commonly called Sensors because they “sense” a physical change in some characteristic that changes in response to some excitation, for example heat or force and convert that into an electrical signal. Devices which perform an “Output” function are generally called Actuators and are used to control some external device, for example, movement or sound.
Electrical Transducers are used to convert energy of one kind into energy of another kind, so for example, a microphone (an input device) converts sound waves into electrical signals for the amplifier to amplify (a process), and a loudspeaker (an output device) converts these electrical signals back into sound waves. An example of this type of simple Input/Output (I/O) system is shown below:
The table below shows common sensors and transducers.
| Quantity beingMeasured | Input Device(Sensor) | Output Device(Actuator) |
| Light Level | Light Dependant Resistor (LDR)PhotodiodePhoto-transistorSolar Cell | Lights & LampsLED’s & DisplaysFibre Optics |
| Temperature | ThermocoupleThermistorThermostatResistive Temperature Detectors | HeaterFan |
| Force/Pressure | Strain GaugePressure SwitchLoad Cells | Lifts & JacksElectromagnetVibration |
| Position | PotentiometerEncodersReflective/Slotted Opto-switchLVDT | MotorSolenoidPanel Meters |
| Speed | Tacho-generatorReflective/Slotted Opto-couplerDoppler Effect Sensors | AC and DC MotorsStepper MotorBrake |
| Sound | Carbon MicrophonePiezo-electric Crystal | BellBuzzerLoudspeaker |
Generally, all types of sensors can be classified as two kinds, either Passive Sensors or Active Sensors. Active sensors need external power, while a passive sensor does not need any additional power source or excitation voltage.
Keep an eye out for our next articles, where we dive even further into analogue and digital electronics.
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