Infu T

Ftg. i Power supply, total count 3s eight, and two counts are used for a space, the six remaining counts are reserved for the dash with a ratio ot two to six (one to three),

7493 Truth Tabte count C B A

6 110 7 111

The dot generator is a simplification of the dash generator, requiring only the outputs QA and QB to generate [he dots. As long as the paddle is held in the dot position. U3 pin 3 wilj be forced high, resulting in a low on pin 12 of U3 If the dash generator has completed its cycle, pin 11 of U3 w ill also be low I he resultant high on pin 13 ol U3 will result in pin 6 of U6 being hekl high, blocking the dash generator, and pin 9 of U3 being driven low, allowing the < lock pulse to toggle U2. Since the1 output is taken from QB, the dot-to-space ratio will be two to two (one to one). The dots will continue until the paddle is released and QA and QEi are both high (i e . the last dot is completed),

The pulse generator (Fig. 2) is a standard 555 circuit with minor exceptions. When varying the frequency in the normal manner, the resistance in >enes Aith the capacitor (the time-constant RC) is varied, which causes a nonlinear change in the charging current of the capacitor, forcing most of the frequency change to take place on one end of the control By use of the potentiometer placed between the 12A suppl\ and the 5 \ supply the current supplied to the RC network will be lin ear The frequency change will no longer have all of its change on only one end of the control. A decoupling capacitor (about 10 uF) can be connected to the center arm of the potentiometer to ensure maximum linearity, it so desired. Switch S1 can be used if desired to obtain a wider speed range With the switch incorporated, the speed is about 5 wpm to JO wpm m slov, (S1 open), and about 10 wpm to 40 wpm tn high (S1 closed),

The keying circuit: is the output NAND gate, U4, the 10k resistor, and the 2N3904 transistor This circuit was chosen to drive my Heath-kit® HW-104 transceiver. If your transmitter requires a different ke\ mg method you may redesign the out put or insert a relay.

The 5-V supply (Fig. 3) is a 7805 regulator from the 12-V supply (most modern equip ment is solid state and designed to run from 12 V), The ,33-uF capacitor and the 1-uF capacitor are those recommended b\ the many facturer when using the regulator.

As with all digital circuitry, a liberal sprinkling of decoupling capacitors should be used on the 5-V supply (one 1-uF capacitor at each device should be sufficient) Construction can be printed circuit if you cane to lay out a board, or wire-wrap as mine is. I used 100-rntf-spacing perfboard and wire-wrap sockets (both from Radio Shack) and wire-wrapped the circuit (using the little hand tool that Radio Shack sold me) when I was watch ing TV one night The dis rrete components I mounted on a DIP header, I wire-wrapped a socket for them also The cabinet is one oi the small metal cabinets from the same source You can either purchase a paddle or make your own as I did If you have a surplus store in your area, look for a telephone polar reiav. After the coii is removed, the remaining met hanical makes

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