Analog sensors

Analog sensors are the simplest and cheapest option if you need to take some measurements. They measure the quantity we need (temperature, current, voltage, etc.) and generate an output signal proportional to the measured quantity. Most often this will be a change in voltage. For example, the zero value of the measured value will correspond to a voltage of 0 V, and the upper limit of measurement will correspond to the maximum permissible voltage (for the simplest DIY systems - 5V or 3.3V)

Due to their simplicity, analog sensors will be the cheapest to manufacture. In this case, there is usually no measurement delay - a change in the measured parameter is almost instantly transmitted to the sensor output. Ease of connection is also important - three lines are enough - power, zero and analog signal output. Moreover, the analog signal is not even necessarily converted to digital - it can be used in an electronic circuit directly to switch relays and as a control signal for other components (transistors, thyristors, etc.) In fact, at an early stage in the development of electronics, the entire system could operate on analog signals, without the need for microprocessors.

At the same time, analog sensors have much less flexibility of use. The range of the measured value must be precisely known, and the sensor must be calibrated for each individual case. After all, the wire with which the sensor is connected itself introduces an error - due to its own resistance or external interference. In fact, two identical sensors may produce different results depending on the connection conditions, wire length and other factors. This problem can be partially solved by shielding the signal wires and calibrating each sensor, but these are additional complications that we would like to avoid.

If we want to use a signal from an analog sensor in a digital system, then we will need an analog-to-digital converter (ADC). It will convert the analog signal into a digital one, understandable to the microprocessor. Some microprocessors (for example Arduino) have built-in ADCs. Some (Raspberry Pi, Orange Pi, etc.) will require a separate ADC. Moreover, the measurement range and accuracy will depend not only on the sensor itself, but also on the ADC parameters. If the ADC, for example, is 10-bit (designed to recognize 1024 signal levels), then even with the most accurate sensor we will not be able to obtain an accuracy better than 1/1000 of the measured value.

Another limitation of the use of analog sensors is the number of inputs to which they can be connected. Microcontrollers usually have a limited number of analog inputs (for example, for a standard Arduino it is 6 inputs, Arduino Mega - 16 inputs). This is sufficient for simple systems using several sensors. If we have many measurement points, then we will need to use an intermediate ADC with the appropriate number of inputs.

Thus, mastering the connection of analog sensors is very desirable when mastering circuit design and creating electronic circuits. For projects using microcontrollers, the use of analog sensors has certain limitations and is used for simple projects.