The aim of the Master's thesis is to make a test circuit, which can carry out the necessary emergency light tests via the Internet. The circuit can perform the functional and battery tests of the emergency light – both required by law. With the obtained results, one can find out the type of error in case of the emergency light failure. For the thesis, the Beghelli's emergency light, model Aestetica, was used. The light uses NiCd battery.
The developed test circuit prototype is meant to be installed inside the housing of the emergency light. It is powered from the emergency light power supply, i.e.: the mains. The test circuit cooperates with the emergency light circuitry that charges the battery and converts the voltage for the light bulb. The main part of the test circuit is the ESP8266 NodeMCU platform. It is designed to control the components during the test and to connect the circuit to the wireless network. Using WiFi, the device is connected to the broker via the MQTT protocol. The test circuit can perform a short or long test. The short test lasts only for a few seconds. The functional test of the emergency light is performed, that is the light bulb and battery voltage are tested. Thus, the basic assessment of the emergency light state can be quickly obtained. The battery voltage is measured using a voltage divider and the analog input of the ESP8266 NodeMCU platform. Besides the basics, the long test also measures battery capacity and determines its SoH value. The integrated circuit LTC4150 is used. Fully charged battery is discharged while the LTC4150 measures the amount of elapsed charge and converts it into pulses. A chain of resistors is used for that purpose. The measurement yields an accurate value of the current battery capacity and consequently its SoH value. Since the discharging current must not be too large, the duration of the long test can be considerable.
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