Recent advances in the development of Internet-of-Things (IoT) devices have enabled researchers to apply such on building automation systems (BAS). Especially in existing BAS, one big challenge is the diversity of communication methods. In such systems, gateways are required to connect various devices. However, while there are very few IoT-gateways able to interface a wide variety of common sensors and actuators, those often implicate high costs, entailing inacceptable investments for larger field tests. To overcome this issue, we prototyped a low-cost plug-and-play and freely programmable IoT-gateway, which supports common analog signal interfaces like 0-10 V or 0-20 mA current loop, and digital ones via RS-485 serial communication. The gateway is based on the ESP32-PICO-KIT development board, a fully functional board with a microcontroller and embedded WiFi. Accordingly, we enhanced this board by adding custom-designed peripherals and developing the required firmware for acquiring sensor data and driving actuators. In order to validate the functionality of the interfaces, we conducted an experimental test series. The experiments comprise measurements of inputs and outputs for either the IoT-gateway or the connected sensors and actuators. The results show an average relative error for analog interfaces of 7 %, hence being sufficient for building automation applications. The RS-485 was successfully tested with a Modbus RTU slave device. Therefore, the prototyped IoT-gateway is directly applicable to both analog and Modbus-based sensors and actuators, shows acceptable errors in analog readings and can be manufactured at a relatively low price, facilitating test benches containing several plug-and-play gateways.