Several approaches to re-using Digital Scales rely on intercepting the LCD driving signals and then decoding the display. This method has some advantages since it leverages the design skill of the scale designers and re-uses all the analogue stages leaving the problem as essentially a digital one. So let’s have a look at the signals going to the LCD. If we number the top pin of the LCD connector as Pin 0 and the bottom pin Pin 15. (Looking at the PCB with the LCD connector on the left hand side) we can turn the scales on and let them settle on a display of “0.00 kg”.. we then scope the signals.
For clarity we choose one signal to be a baseline (I randomly chose Pin 0) and make this CH1 of the scope; the other channel then becomes CH2. We incrementally move through Pins 15 to 1. (With Pin 0’s trace being in all images).
Let’s see what we get…
Pin 15 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 14 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 13 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 12 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 11 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 10 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 9 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 8 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 7 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 6 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 5 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 4 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 3 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 2 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
Pin 1 (CH2 Lower Trace) with Pin 0 (CH1 Upper Trace)
