| 摘要 |
<p>1370221 Impulse transmitters STANDARD TELEPHONES & CABLES Ltd 16 March 1972 12354/72 Heading H4K [Also in Division G4] In a selective signalling apparatus, e.g. a push button operated telephone, a set of contacts forming at least some of the contacts operated by pushbuttons to provide a coded condition are connected such that when operated a strobe signal is activated to connect the coded condition to a signal generator. In the instrument shown sixteen buttons are provided with common column contacts X1-X4 and common row contacts Y1-Y4 so that operation of each pushbutton is uniquely signalled to a coding circuit by closure of a respective pair of contacts. A strobe signal is provided for transmitting on the output of the coding circuit and this strobe signal is generated when any one of contacts X1-X4 are operated. Since one of these contacts will always need to be operated a separate common strobe signal contact can be dispensed with. Preferably the contacts X1- X4 close after the contacts Y1-Y4. In a modification each pushbutton controls its own pair of contacts one of which is connected additionally to the strobe signal supply, Fig. 3 (not shown). Diodes are used to ensure that spurious operation does not occur.</p> |
