Two-variable-led-matrix-display

  
This matrix can show the values of two variables, for example, frequency and voltage. The display is a graph made from a matrix of LEDs. The LEDs on each axis are color coded, red for out of tolerance and green for in, fanning a red band around the inner green rectangle. The two input voltages proportional to the functions being measured are presented to the two columns of comparators. The other comparator input is a reference voltage derived from resistor ladder Rl to Rx. The output of each row of comparators is processed with an inverted and an AND gate to allow only one active output for any input value.
Two-variable-led-matrix-display - schematic

The LED at the intersection of the active drives shows the relationship of the two inputs. The advantage of this display is the ease in reading, modification, and also its small size. All comparators are LM339 quads.




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