## 4 Laboratory Overview  
With the aim of introducing students to biometric acquisition, we have designed a laboratory which simulates the entire acquisition process. In order to take better advantage of practical equipment, we have decided to apply the flipped-classroom approach. This approach inverts the classical approach to lecturing and homework. As stated in [21], when a classroom is \"flipped\", what is usually done for homework is done in class, and what is usually done in class is done for homework. In this way, students can benefit from the help of instructors when solving more complex tasks, like case studies or laboratory exercises. In our case, before each lesson, students were given lecture notes with basic concepts required for the class along with instructions for the following laboratory exercise. Our course consisted of two parts--the acquisition process and the result evaluation. Each part had two lessons. In the acquisition phase, biometric sensors, a temperature sensor, and a humidity sensor were connected to Raspberry Pi 4. Biometric sensors were connected via the USB interface, while the humidity and temperature sensor sent data via the radio connection. The Raspberry Pi, and the sensors and the integrated components create a biometric acquisition surface. In the laboratory, there are several biometric acquisition surfaces. From each surface, the extracted biometric templates with environment metadata are sent over the network to the server application, which stores them in the database. Environmental conditions can be controlled from the central server console provided by the server application. The server application can pass instructions to biometric acquisition surfaces in order to create a desired acquisition environment. For example, the heater can be turned on to raise the temperature to the desired level. Collected data is available for further evaluation, as students can access it with appropriate tools during the second part of the course. The architecture of the fingerprint acquisition laboratory is shown in Figure 1.  
In the acquisition phase, each of the participants provides several samples of the index and middle fingers of both hands in the various environmental conditions. The acquisition phase has three parts. In the first part, participants provide fingerprints in normal environmental conditions, at a temperature between 20 and 24 \({}^{\circ}\)C. In the second part, wet, greasy, and wrinkled fingerprint images are collected, besides the fingerprints taken in normal conditions. The laboratory temperature for the second part of the acquisition is also between 20 and 24 \({}^{\circ}\)C. The final, third part is done in a warmer environment, with a temperature between 35 and 40 \({}^{\circ}\)C. In order to achieve such a higher temperature, a special environment for fingerprint acquisition was created. Other conditions are similar to those in the second acquisition session. For acquiring images in higher temperatures, a Plexiglas box was built. The box has a height of 40 cm, length of 70 cm, and width of 45 cm. There is a round hole with a 15 cm diameter, through which the participants can access the fingerprint sensors. For proper heat isolation, the box was wrapped in Styrofoam. Raspberry Pi was used to control three heaters (RC016-8W) and a power rectifier. The heaters were placed on a metal grid inside the metal box. On the other side of the grid, several ventilators were placed. The ventilators were used to move the heated air to the other parts of the Plexiglas box. Heat sensors were placed on two locations inside the Plexiglas box and connected to the Raspberry Pi. If the temperature falls below the value designated for the acquisition scenario, heaters are turned on. The Plexiglas box and the sensors are shown in Figure 2.  
Figure 1: Fingerprint acquisition laboratory architecture. Figure 2: Fingerprint sensors and other equipment used for the third acquisition session. Depending on the environmental conditions, the quality of the biometric sample can vary.