Distance sensors and motion detectors in microelectronics
In the standard equipment of every hobbyist at least one motion detector or distance sensor can be found with a pretty high probability. And there is a good reason for this, because this is the only way to realize great projects like a line tracker chassis or an efficient light control within your own four walls.
The function of motion detectors and distance sensors is easily explained. Both sensors use infrared technology, the motion detector registers temperature changes (e.g. due to body heat) within the field of view. If an increase in temperature is detected within the PIR range, the motion detector passes on a signal. The level of the threshold until the signal is output is often calibrated with a trimming potentiometer directly on the module.
Distance sensors function in a similar way: There is an infrared light emitting diode on the sensor, which emits infrared light that is not visible to humans. A photo resistor (LDR) is mounted in the immediate vicinity of the diode. If an object enters the PIR range of the sensor, it reflects the infrared light of the diode. The LDR detects fluctuations in the incidence of light and passes them on in the form of an electronic signal for processing by a logic unit.
Other sensors for measuring distances
A popular module for measuring distances is the HC-SR04 ultrasonic sensor. Unlike the sensor types described above, the HC-SR04 module does not work with an infrared signal, but with ultrasonic waves. The ultrasonic sensor emits waves in any direction and measures the time until they return to the HC-SR04. From this, the distance between an object and the HC-SR04 ultrasonic sensor can be measured in real time and even displayed visually.
The functionality of motion detector, distance sensor and ultrasonic sensor at a glance
Motion detector (PIR sensor) HC-SR05:
- detects temperature differences in the PIR range
Ultrasonic sensor HC-SR04:
- measures the distance to an object using ultrasonic waves
- measures changes in the incidence of light using a photoresistor