Circle S M Re Ao Er Service Card

urut containing ihe bank switch). As long as the switch remains in Hank 4, the selector can pull the appropriate lines lou and step through the banks,

I he signals intended for the voice synthesizer arc narrow and rapid, and vary depending upon the frequency to be spoken. They occur in a burM each time you press the voice button so some input signal conditioning is required to prevent false or unreliable triggering of the selector circuit.

In the schematic diagram in Figure I IC I, a 400IB quad NOR gate operates as a monostable multivibrator, or "one shof \ The first pulse, applied to pin 6. fires the one-shot (with R2 and C2 providing the time constant) that remains triggered for the duration of the burst. The result is a single puise of se\eral milliseconds, suitable for triggering IC2.

IC2 is a 40271* dual JK flip-flop, used a* a 2-bit hmary counter. CI and Ri provide a reset pulse when the rig is first turned orit setting the flip-Hop's two NOT-Q outputs to the logic 1 state. Each pulse from IC1, corresponding to a press of the voter button, advances the count one step in its binary sequence. Diodes D1 and D2 permit the ilip-flop to pull the radto s bank switch lines low, but block logic 1 voltages (5 volts) from reaching the radio.

Construction Details

Figure 2 shows a full-sized foil pattern, but any type of construction uill do. The board should be made to the same overall dimensions. though. s<> thai it will fit in the space intended for the voice board.

The radio s connectors are on standard

0 1-inch centers, but the matching sockets are simply not available in the U.S., as far as

1 can tell. Usable connectors can be made from standard male 0.2 5-inch high* header" type pins, available from Jamcco Electronics and Digi-Keyt The pins are a little slim, though, so bend them just a little to insure a good connection. The 2-pin connector should be attached to the selector board by about 5 inches of 2-conductor wire, and can be made from the same type pins, bent at a right angle. You can also use a right-angle header. La> the board solder side down so that the two rows of four holes are facing left, and lay the wire assembly to the left of the hoard, with the pins facing up. Now, connect the wires to the two outermost holes nearest the front of the board, making sure there are no twists in the wire. (See Figure 3-)

When installing CI, Dl and D2< be sure CO observe proper poiarity. And, of course, be careful thai the ICs are correctly insereinstallation and Operation

Disconnect power from the rig and install the board, with the connectors on the left, and screw it down with two screws. (See Figure

3.) Now, locate the radio's tuo connectors, which will be lying 'iear the installation location. (If you're not sure where to install the hoard, see page 44. section 9-5. of the owner's manual. > Install the 8-pin connector with its flanges facing left, and the 3-pin one the same way. Finally, take the selector's 2-pin and press it into the top of the REAR two pins of the four-pin on the right of switch unit F (just to the left of the installation site), gently pulling the existing wires to the left in order to make room for entry. See Figure 4 for connector details.

Close the rig up, reconnect power, set the Kink switch to Bank 4. and fire it up. Press the scroll button until the LCD displays a memory location. The first number should be

4. indicating Bank 4, Press the voice switch, and it should move to Bank 3, Each press will increment it by one. If the order is incorrect, you may have wired the selector "s 2-pin backwards. The easiest way to correct it is to reverse the wires going to the board, and leave the connector alone. Be sure to completely remove it from the radio first, to avoid any potential static problems or short circuits.

A Bonus

The selector resets to Bank 4 upon power up, effectively making it disappear. The bank switch still works and can be used to preset the rig to a specific bank for timer recording of shortwave broadcasts. Don't forget, though, to set it back to Bank 4 for normal operation. If you leave it in another barik the banks won't step properly, but no damage will be done. Just reset the switch and all will be fine. Enjoy the other memories in your ■■.m'lH

Michael Jay Geier KBl UM invented ihe Memory Bank Selector in ¡986L It was marketed b\ Invent ran Labs as Vie Banker '' in ¡987. KB!UM h 73'% troubleshooting "Ask Kahoom' columnist. You can reach him at PO Box 64766. & Burlington VT05406.

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CIRCLÉ 382 ON READER SERVICE CARD

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