Printer Sharing Box

03 PRINTER SHARING BOX This simple circuit makes it possible to connect two computers to a single printer. Toggle switch Sz selects the rel- evant computer by applying the appro- priate logic level to the enable inputs, G, of octal bus transceivers Type 74LS641 (ICI. IC4 incl.). The direction input, DIR, of these is hard-wired to +5 V, so that the data direction is from An to Bn. When G is logic high, the buffers are switched to the high impedance state, so that chip outputs can be con- nected to form a bus structure. With this in mind it is relatively simple to see that the circuit is the electronic equivalent of a 16-way toggle switch. Parts list Resistors (±5%): R ;112;115;118= 10K 83;84;86;R7= 8-way SIL resistor network 10K 89=1K01 Capacitors: C1;C2;C3 = 22n Semiconductors: IC1 . . .IC4 incl. =74LS641 Miscellaneous: Si = miniature toggle switch. S2 = miniature toggle switch. K1;K2;K3= 36-way terminal strip block. PCB Type 884030 (not available ready-made through the Readers S...