Patent GB-275715-A (GB)
Title: Improvements in or relating to keyboard arrangements for automatic or semi-automatic telephone plants
IPC: H04M1/272
Filed: 1926-05-10
Abstract: 275,715. Marks, E. C. R., (Automatische Fernsprech-Anlagen-Baw-Ges.).May 10, 1926. Semi-automatic exchange systems. - A keyboard equipment having a separate row of keys for each digit is provided with a number of starting keys one for each row, the arrangement being such that the keyboard may be employed for numbers having any number of digits less than the maximum the starting key corresponding to the last row of keys used being operated in each case. Thus in the equipment shown with provision for numbers having a maximum of six digits, in order to transmit the number 219, keys t2, t1, t9 and the starting key An3 of the third row are operated. Over the starting key, relays HT, ZT, T, F are operated in parallel, relays HT, F, locking in series over contacts 27, whilst relays ZT, T lock over front contacts of relays HT, ZT, respectively. Relay II of the counting chain now energizes over its upper winding, key t2, and contacts 31, 30, completes a circuit for the upper winding of relay I, and itself locks over its lower winding in series with relays O to contact 39, relays B, C, D being operated in succession by the closure of contacts 32. Relay O closes a circuit for relays J, A, the latter sending a control current over the b-wire whilst the former transmits one impulse over the a-wire. Relay J opens the circuit of relays 0, II and on the release of the latter, a locking circuit for relay I in series with relay M is closed. After an interval the relapse of relay O releases relay J, and terminates the impulse. Relay M now operates in a similar manner in conjunction with relay J to send a second impulse after which relays I, M, J, A, release followed by relays B, C, D. After relay C has released but before relay D has released, relay HT is unlocked and releases. Relay ZT remains locked over contacts 28, 15. Relay I is now operated over key t1 and contacts 59, 29, 30 and a second digit consisting of a single impulse is sent in a similar manner. During this digit, relay U which was previously shortcircuited over contacts 49 operates over contacts 48, 46, 15 opening the locking circuit for relay ZT which however remains temporarily locked over contacts 68. Relay U also holds relay T over contacts 70. At the end of the digit the relapse of relay B releases relay ZT and on the subsequent release of relay C, relay U1 operates. On the release of relay U, relay T remains locked over contacts 27. For the third digit, relay IX operates over key t9 and contacts 72, 29, 30 and circuits are closed in turn for each of the relays VIII - - I. The transmission of nine impulses takes place in a similar manner to that explained above for the first digit, relays M, O operating alternately in the locking circuit of the odd and even counting relays, respectively, and controlling the transmission of impulses and the unlocking of one counting relay per impulse. At the end of this digit relay T is released and the whole equipment has returned to normal. The starting key An6 of the final row may be dispensed with, the starting circuit being closed by the depression of any key in this row. In an alternative arrange. ment, the relays HT - - E may be in series and the keys An1 - - An6 in parallel.