TECHNICAL MANUAL FOR COMPACT VHF DSC RM2042

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RM20425.6 KEYBOARD UNIT (MODULE 6) PART NO. 625636The keyboard consist of a 4 times 8 matrix of which 26 keys are used.The 4 rows are set high alternately and by reading the output at the 8 columns it is possible to determinewhich key has been activated. This scanning of the keyboard takes place 100 times per second.The keyboard can be illuminated by 13 LED’s. The voltage accross the LED’s is controlled by the twotransistors Q2 and Q3, placed at the microprocessor (module 2) and the current in each LED is roughly8.5 mA.This diagram is valid for PCB rev. 25636F9505PAGE 5-27