Ac operated version, rear view.
corrected in the included a 33k Ohm resistor with an template drawing). SPST switch in parallel to add
The illumination control is or subtract the 33k to or from the circuit. If desired, the switch and resistor may be replaced with either a 30k Ohm variable resistor or a photocell control of about 30k Ohms maximum resistance.
At this writing, it has been determined that the battery-operated unit is hard on 9 V transistor lotteries, in spite of its low drain in the "low" or "blanked" conditions. A Duracell™ only lasted about 20 hours under a 26 m A load; a regular carbon-zinc battery lasted about 18 hours (both new batteries). Although the clock works satisfactorily on a 9 V battery charger, I learned that the circuit "loads" the charger to about 7.8 volts, and a new battery
inside the unit will supply power to the clock, in parallel, until it is at or below-the input voltage from the charger.
When the clock is on the internal battery, it will continue to function (blanked or low) at terminal voltages below 70 volts, but disturbing the input power (paralleling the battery or applying an external supply) can and does cause glitches, if not done carefully. When glitches are introduced, the displays become random like showing 65 seconds, or a 3 in the tens-of-hours column, or beeping the alarm tone when the alarm is turned off. Under these conditions, the best cure is to remove power completely and restore the correct voltage level; the clock needed resetting anyway, if it is desired to use the pm indicator in the 12-hour mode (rather than display 3 bars), the 12/24-hour selector will have to be a DPDT (center-off) switch, and the date format will have to be the American style (month/ day). Similarly, if only the I 2-hour option is desired, the month/day format must be used in order to access the pm indicator, as the 3-bar output required for a 2 or a 3 is also the pm indicator in the 12-hour mode, and no digit greater than a f<1" can be hrs set mtn set from 6 a tt. 5 or ckrgr
19-uv dc 6-iOV AC
* via blank sw, if desired via alarm om/off switch
Fig, J5(b)L Auxiliary board - battery version — component layout„
alarm SELECT to (7 sparc
INHIBIT TO (3
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