Circle On Reader Service Card

TION SELECT switch. Consult Table 1 for the resistor values. Just to make sure thai those values fit your meter» connect

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Photo Ft. The finished Box.

Meter driver

The meter step function resistors and the meter flip-flop are in the lower left side of Photo A. A piece of multicolored cable connects ihc resistors to the FUNC-

one resistor, the meter anil a hattery, 1-1/2 or 3 volts. in series. It lakes just a couple of minutes to do these suggested pre-construction tests, but it can save a loi of time il >ou have an undesirable value. It takes me longer lo remove wrong parts from a hoard than it did lo put them on the board in the first place.

LED driver

The LED driver circuit is on the right side of the board. Note thai the transistors Q5 and Q6 are rotated I St) degrees from each other. That makes it easier 10 connect their emitters together. I did the same thing on the other two circuits that use a flip-flop.

You will want to pre-tesl the LEDs. This will tell you which lead goes to the plus side of the batterv. It will also tell you iJ you have the right si/.e current-limit resistor; With loo small a resistor, the LHD w ill get quite bright and prob-ablv quit working. With loo large a resistor, the LHD will not give off enough liiiht.

Speaker driver

The sound generator is on the top right side of the board. The smaller capacitors in it allowed a tighter layout, After >ou wire it. you can lest it with anything from 1-1/2 to 9 volts. The loudness and the lone will change with the voltage. When you conned the bat-terv. if it gives just a loud click in the speaker, remove the haliery and recheck the wiring. A missinn L>r wronjj f v C

value resistor or capacitor can cause that problem, as can an incorrectly connected transistor.

Auto-Off switch

File Aulo-Oft switch is on the back left side of the board. The complementary output stage uses TIP series transistors because the\ give lower voltage p -w w drnp than 2N3900 scries transistors in this application.

To lest the switch, vou can connect a baiters and a voltmeter—or better yet. one of the other circuits from the Box— in the collector of Q3 and bauerv minus. Battery plus goes lo the collector of Q! and the emitter of Q3.

Ii you have switch I wired you mav push it. or momentarily conncct CI and 38 73 Amateur Radio Today • November 1997


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