In the column, row scanning and detection circuit of digital computer LED writing board
, a subgroup coding scanning frame is used, with its operating principles and the wiring shown in FIGS. 11 and 12. The sub-group electrode lines on PVDF piezoelectric film are divided into several high groups while the frequency of scanning clock (approx. 4 MHz) is divided by a binary counter, also divided into high and low groups for pushing the multiplexer of high group (collective group I to 1 multiplexer on FIG. 12) and low group (dispersed group J to 1 multiplexer on FIG. 12) to scan fine electrode line group.