Grove - force sensors and limit switchers

How do pressure sensors work and what are they for?

Regardless of the application, limit switches and pressure sensors in practice are only responsible for two main functions: switching on and off electric circuits. To illustrate how such sensors work, it is worth giving an example of a refrigerator. When you open the refrigerator, the bulb inside lights up. Similarly, the bulb will go out when it is closing. The light inside the refrigerator will turn off because the lighting inside the refrigerator is only needed when you look inside. How was this effect achieved?

This process is carried out just by the limit switch. The pressure sensor receives information that the refrigerator is opened (pressure released) and the refrigerator closed (pressure applied). A properly programmed device simply performs a simple action automatically: it turns the light on or off.

The use of pressure sensors is very common. In practice, you will find them in a multitude of devices that you have around you, both at home and at work. For example, in washing machines and in microwave ovens, the sensor turns off the voltage of the control and operating circuits of these devices when the door opening is identified. One of the most important functions of this type of device, responsible for our safety, works in this way. The limit switch serves as a protection against damage to the device and from injury to the user.

Pressure sensors – they are all around us!

The use of pressure sensors is not limited to household appliances and audio / video devices. However, in large factory machines and on production lines in industry, limit sensors perform similar functions as in household appliances. When the industrial robot encounters a breakdown and malfunctions, the limit switch disconnects the power to the control system and the robot's drive. Thanks to this, it ensures the safety of employees and manufactured products that could be damaged.

In construction machinery such as dump trucks or excavators (and even in city buses and public transport), the sensor will activate the acoustic generator of a cyclic warning signal while the vehicle moves backwards. This signal is designed to warn outsiders that the vehicle is reversing - certainly we all know it, because it is not one of the most pleasant. In this category you will find various similar force and pressure sensors. They are compatible with programmable electronics such as Arduino or Raspberry Pi. For example, the Grove limit sensor, when changing the position of the contact lever, sends a binary signal to the digital input in Arduino, informing about switching the circuit on or off.

Resistive pressure sensors – application examples

A variation of the presented devices are the FSR resistance force sensors. FSR sensors use in their construction a surface element with a variable resistance value. The resistance varies with the force of pressure. The surface of the FSR sensor is made of two layers - conductive and dielectric - separated by air. Applying pressure to the sensor will cause its conductive layer to deform, which will further reduce its resistance. Similarly, after removing the load from the sensor, the resistance level of the conductive layer will increase. Resistive pressure sensors are used in electric musical instruments (drums, keyboards), as well as in car control systems.

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