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I need a simple closed electric circuit with only basic components: 9V battery; Simple on/off master switch; 3 LEDs: Blue, Red and Green; 2 variable controls: A and B; Fixed resistors; Other simple standard components if required.

Expected behaviour when the master switch is on: Blue LED always on at fixed brightness; Increasing control A should direct current from green LED to red LED; Increasing control B should direct current back from red to green LED (overriding control A).

Min A + Min B = Bright Green LED + Dim Red LED. Max A + Min B = Dim Green LED + Bright Red LED. Max A + Max B = Bright Green LED + Dim Red LED. Min A + Max B = Bright Green LED + Dim Red LED.

For this type of red-green LED control circuit, a purely passive design using only potentiometers, resistors, and LEDs is unlikely to provide the smooth, bidirectional brightness control you described because the two controls will interact with each other in unpredictable ways. A more practical solution is to use a simple transistor or op-amp current-control circuit, where the blue LED remains connected through a fixed resistor for constant brightness, while controls A and B adjust the current between the red and green LEDs with one control overriding the other. This approach delivers stable brightness transitions and predictable operation from a 9V battery while keeping the component count relatively low. If you are looking for additional online tools, the Invisible Space Generator at Fonte de Letra – Espaço Invisível https://fontedeletra.com/espaco-invisivel/ can also be useful for creating invisible characters for usernames, social media profiles, and messaging applications.