GB1410811A - Keyboard apparatus - Google Patents

Abstract

1410811 Keyboards PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 14 Nov 1972 [17 Nov 1971] 52505/72 Heading G4H Keyboard apparatus comprises an array of keys and an individual bi-stable element associated with each, and an interrogation unit which repetitively and successively interrogates the keys to produce an output corresponding to each key after actuation thereof and set the corresponding bi-stable to block further output from the key, and reset the bi-stable when the key has been de-actuated. In Fig. 1, a counter T driven by a clock Cl interrogates in turn the columns of the matrix of keys K11 &c. shown. If, for example, K11 is depressed, interrogation of its column produces an output from AND A11, via AND N11 enabled by the reset state of bi-stable FF11, to output B11, this output being fed back to set bi-stable F11, preventing further output at B11 until the column is interrogated at a time when the key K11 is not depressed. When this happens the absence of an output from AND A11 enables AND G11 via inverter I11 to reset bi-stable FF11. The output at B11 &c. can be encoded into serial or parallel binary form. The row conductors R1, R2, R3 are redundant unless the array of key switches is separate from the rest of the circuit, the latter being provided in integrated circuit form connected to the key array only by the row and column conductors. The diodes D11 &c. can be dispensed with if the attenuation at a closed key switch prevents incorrect enabling of an AND such as All when two switches are closed together.