So as we see, sensors are analog devices, if we need to connect some sensor to a microcontroller in some project, we need an analog to digital converter (ADC) to convert it from an analog signal to a digital signal.

Active sensors have its own source of light or illumination. In particular, it actively sends a pulse and measures the backscatter reflected to the sensor. But passive sensors measure reflected sunlight emitted from the sun. When the sun shines, passive sensors measure this energy.

An active sensor is one which transmits a signal into the environment and then measures the response that comes back. One example is an ultrasonic system: A pulse of ultrasound is emitted. The sensor detects it.

Examples of passive components are resistors (R), capacitors (C), inductors (L), transformers, antennas, potentiometers (variable resistors), diodes (one-way conductors) and the like.

The most common form is the LDR. This stands for Light Dependent Resistor. A piezo sensor/transducer is a passive element and works both ways. When a pressure is applied (sound) an electric voltage is generated.

Since the conventional diode has no negative differential resistance it will not be active and since it dissipates electrical energy it can be considered as a passive element.

Example of active transducer is bourdon tube. Example of passive transducer is LVDT (linear variable differential transformer). It generates electric current or voltage directly in response to environmental stimulation.

What kind of sensor is the LDR Sensor? Explanation: The LDR sensor is a passive sensor since it requires no external supply of voltage in order for it to work. It simply acts as a variable resistor and changes the resistance of itself while light of varying intensity falls on it.

Sensor Specifications

Photo resistors, also known as light dependent resistors (LDR), are light sensitive devices most often used to indicate the presence or absence of light, or to measure the light intensity.

LDR advantages

• High sensitivity (due to the large area it can cover).
• Easy employment.
• Low cost.
• There is no union potential.
• High light-dark resistance ratio.

Disadvantages of electrochemical sensors include:

• Narrow or limited temperature range.
• Short or limited shelf life.
• Cross-sensitivity of other gases.
• The greater the exposure to the target gas, the shorter the life span.

Advantages of LDR Sensor ③ The frequency response (the ability of the device to detect the fast changing optical signals) is very low. The internal photoelectric effect has nothing to do with the electrodes (only photodiodes do), that is, DC power supply can be used.