Multi-contact brush type fish detecting sonar

A multi-contact brush type fish detecting sonar, comprising

• a. a plurality of cascaded delay circuits each having an input terminal, a transistor, a differentiating circuit connecting said input terminal to a base of said transistor, and an output terminal connected to a collector of the transistor the output terminal of each delay circuit being connected to the input terminal of the next succeeding delay circuit;
• b. a plurality of holding circuits each having two diodes, a signal input terminal of each holding circuit connected to one of said two diodes, means connecting the other of said two diodes to the corresponding output terminal of one of said delay circuits, a holding signal output terminal, a capacitor means for coupling a terminal of said capacitor to the anodes of said two diodes for holding a sonar return signal to be recorded when a delay output pulse from said corresponding delay circuit and the reflected sonar signal applied to said signal input terminal are concurrently applied to said two diodes;
• and
• c. recorder means with a plurality of contacts connected to the output terminals of said holding circuits, respectively, a slidable brush, and a recording pen slidable over a recording sheet in unison with said brush which slides over said contacts.