1,183,572. Calculators; counters. NATIONAL RESEARCH DEVELOPMENT CORP. 4 April, 1967 [4 April, 1966; 23 May, 1966], Nos. 14860/66 and 22770/66. Headings G4A and G4D. Two manual starters are provided in binary arithmetic equipment having three electromagnetic relay registers, the relay contacts forming a parallel adder to add the contents of two of the registers into the third. Fig. 1 shows a stage of the adder, two relays or manual keys respectively controlling the contacts a and b in accordance with the addend and augend bits. IC is the carry-in line, receiving battery + or earth E depending on the carry value. OC is the carry-out line to the next stage. The sum bit is indicated by the lamp ILP. Alternatively, contacts a 7-9 and b 1-3 can be controlled by one relay or key and the other contacts by the other. A calculator for teaching computer operation fundamentals has a 4-stage parallel binary adder, with stages as above, except that the lamps ILP are replaced by sum relays (RLS) forming a bank of four. A second bank of four relays (RLB) is set with one operand by manual switches (I A to I D ) the switch settings being entered into the relays in true or complement form (F 3 ) according as addition or subtraction is required. The other operand is established on a third bank of four (RLA) in accordance with a one-out-of-n decimal key actuation, coded into binary form by a diode matrix, the matrix paths from the 1, 2, 4 and 8 keys to the respective binary relays being coloured differently from the other connections for pedagogic purposes. The second and third banks (RLB, RLA) control contacts as in Fig. 1, the sum relays (RLS) charging associated capacitors so that the sum can be transferred to the third bank (RLA) straight or with shift. The relays are visible and aligned with the corresponding switches and with lamps indicating the relay states. Multiplication and division are performed by repeated addition and subtraction respectively, subtraction being by complemented addition (see above), and end-aroundcarry being provided in the adder when subtraction and division are being performed. If the capacity of the " sum " relays (RLS) is exceeded or a negative result is obtained, the most significant carry line inhibits operation. A machine cycle (e.g. one addition) occurs each time a press-button (P) is pushed. Alternatively, operation can continue automatically as long as a manual switch (Q) is closed and optionally until a binary counter (Figs. 6A-6C), counting the number of cycles, reaches capacity. Since the initial counter reading can be preset manually, the number of cycles can be preselected. Multiplication by repeated addition can thus be done automatically by setting up the multiplicand on the second relay bank (RLB), and the complement of the multiplier in the binary counter. An electromechanical decimal counter, with display of count, also counts the number of machine cycles. Capacitors shunt relays in control circuitry to slow down machine operation. Binary counter (Figs. 6A-6C).-Pulses to be counted each actuate a relay (not shown) to momentarily reverse the movable contact RLY3 (Fig. 6C, right). The first such pulse thus causes charged capacitor CA to actuate relay RLC.A which holds via RLC.A2, allows C A to discharge via RLC.A1 when the count pulse ends, and allows capacitor C B to charge via RLC.A3. The second pulse connects the discharged capacitor C A across RLC.A to cause it to release thus allowing C A to charge and connecting charged capacitor C B across relay RLC.B causing it to actuate &c. The third pulse actuates RLC.A without affecting RLC.B and the fourth releases both and actuates relay RLC.C, and so on, the relays RLC.A to D thus counting in binary fashion. On a count of 15, the circuit across ML (bottom of Figures) is broken. The counter may be preset at any desired value by means of manual switches 1A to 1D and SET.
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