Many people are irritated by the superfluous zero that precede a number on, for instance, a liquid crystal (Lc) display. To them ‘1’ is clearer than ‘001’. In systems where the ICL7106 display is used, this irritation may be removed by the present suppress.
Both the backplane (BP) and the segment of a 1CL7106 arc driven by a rectangular signal. When the segment is actuated, the drive _signals are in antiphase: when the segment is inactive. the display remains dark because the drive signals are in phase.
Suppressing superfluous zeros is, therefore the fairly simple matter of finding these zeros and inverting the signal that drives the segment.
A 3 1/2 digit display has three complete digits numbered 1, 2, and 3. The fourth (half) digit is driven via output AB and can only show 1.
Whether digit 3 has a leading 0 is easily found out, because if digit 4 is not used (AB is off) and a digit, 3 segment g is off While segment e is on, there is a leading 0 on the display. In that case, the drive signal to the segments for digit 3 may be inverted with XNOR gates, whereupon the digit goes out.
In the case of digit 2, it must be checked whether digit 3 is off and whether a 0 is displayed via digit 2. The latter may be determined from the state of segments e and g. If it is the case the drive signals for digit 2 must be inverted.
Opamp IC 9a buffers the level of the test output so that this may serve as the earth level for all connected circuits.