A blade for mounting to a scraped surface heat exchanger drive shaft by pivotal connection with a mounting pin has a blade body having a first side and a second side, and a scraper edge and a hinge edge. A flexible optical conductor is connected at one end to one of the boards. In a transmission system using such a Viterbi decoder and transmitting equipment, the flexibility relating to the standardization, designing, maintenance, and operation of equipment is increased and reduction in running cost and increase in reliability can be attained without deteriorating the performance or service quality. Each emitting element is connected to the first conducting overlayer and the first conducting overlayer includes vias through which each connecting lead from the emitting element to the switching control circuit extends.