You never notice how often the power goes off until you start fooling around with computers. A great majority of power interruptions go unnoticed in normal every day living. Unfortunately, that computer notices every one. The reaction is always the same. The screen goes blank and back come the opening copyright notice; gone is your program, data, document, or whatever.
With the Timex 2068 the solution to this problem is simple: a battery back-up to the regular wall outlet along with a charging system that keeps the battery fully charged.
Sound complicated? All you need are a few parts from your Radio Shack store and the battery. I happen to use two 6 volt 8.5 A.H. Gel-cell batteries in series (for 12 volts). These are really overkill. These just happened to be on hand and have run the computer for several hours when I forgot to turn the computer off.
I used a Radio Shack plastic case and mounted the female power plug in one end, fed the wires for the male plug through a hole cut in the opposite end, and ran the wires for the battery out the side. All other electronics are mounted in the box. Wiring is as shown in the schematic diagram.
In normal operation, power is supplied from the 2068 power supply, through CR2 to the computer. If the power goes off for any reason, the battery continues to supply power to the computer through CR3. Diode CRI keeps the battery from discharging through the 2068 power supply and provides power through the 120 ohm resistor to keep the battery charged. This resistor will normally run warm. The one watt size was chosen to act as a fuse in case the battery shorts or puts too much load on the 2068 power supply. Better to replace a resistor than the power supply.
Note: This circuit is intended to keep the battery charged and not to recharge a totally dead battery. To attempt to do the latter may destroy the resistor.
