Digital Water Level Indicator using XOR Gates

Each LED is in place of of a single Seven Segment Display with each LED representing the first letter of the value it represents. CONSTANT represents the three pins of the Seven Segment Display which will always be on, therefore reducing the number of jumpers needed following each resistor/diode from the output of the XOR Gates. This is a college project. My tutor told me I would need signal diodes to stop the back flow of the current but I believe the XOR Gates to render the use of the diodes obsolete. I have tested this theory within the emulator & have had the expected result. I haven't put this theory into practice as I'm too lazy to de-solder & move components & jumpers around on my Vero board.