Arduino is an open-source platform intended for the purpose of creating various electronic circuits and devices. From some simpler measuring instruments (since it is very compatible with various types of sensors and has the ability to measure almost all physical quantities) to some more complex robots. The main parts of an Arduino are microprocessor (type of a microprocessor depends on type of Arduino board), analog and digital inputs and outputs, power pins, a USB connector, and a power connector. The input signal can be analog or digital, while the signal from the Arduino outputs can be a digital or PWM digital signal intended to perform the functions of the analog signal since mean value of the signal can be controlled with PWM method. The signal that is fed to the analog input of the Arduino, through a 10-bit ADC, is converted to the appropriate digital level at each clock cycle (one of the possible 1024 since the 10-bit resolution allows 210 different levels). The only physical quantity that the Arduino has the ability to read directly through the analog inputs is the DC voltage so measuring the voltage using an Arduino is no problem. Since the topic of this final thesis is the production of an ammeter, that is, an instrument used to measure the amount of direct current, it was necessary to somehow convert value of the current into the appropriate voltage amount. In order to achieve a linear dependence of voltage on current, shunts (resistors of large dimensions with small amounts of resistance) were used because the passage of current through them creates a voltage drop whose value linearly depends on the amount of current, as stated by the Ohm's law. Two versions of the ammeter were created, one using a shunt with a nominal resistance of 1 mΩ for measuring currents up to 100 A and the other with a shunt of a resistance of 10 mΩ for measuring smaller currents, but with greater precision. The ammeters, which were made as part of this final work, consisted of four basic stages. The first stage is a sensor, ie a shunt that converts current into voltage. The second stage consists of an operational amplifier in a non-inverting design for the purpose of amplifying the signal generated by the sensor to achieve the possibility of a more accurate reading. The third stage is the Arduino, which reads the signal, executes the calculations and forwards the calculated current to the fourth stage, or LCD display that allows you to display the amount of measured current at any time. However, before the instrument can be created and code written, it was necessary to calibrate the shunt values (using the linest function in MS Excel after measuring the voltage drops for different currents) and the voltage amplification of the operational amplifier because there was a problem of voltage amplification-input voltage dependance. Only after calibration was it possible to write code using the Arduino IDE environment. After the code is written and both ammeters are physically created, the only thing left is to make a few measurements for both ammeters at different currents and for each measurement calculate the percentage error over which the accuracy class of the instruments will be determined. After all the errors were calculated, it was concluded that the error is smaller while measuring larger currents rather than smaller. Ignoring measurements at low currents, it could be concluded that an ammeter realized with a shunt of resistance of 1 mΩ, just like the other ammpeter that uses shunt of resistance of 10 mΩ, belongs to the accuracy class 2.5 which does not make them the most accurate measuring instruments, but still can be precise enough for rough measurements.