ZX hardware - Backup Power for the ZX Spectrum

BACKUP POWER FOR THE ZX SPECTRUM

The mains power may fail while you are typing in a long program. In that situation, you could lose the results of several hours’ work, and perhaps even a program of your own that you are just finishing.

To prevent mishaps like this, you need to provide backup power for when the electricity is off.

This is not complicated or difficult to do, and the effort will certainly pay off. There are several ways to solve the problem. We showed one in issue 2 of ZX REVIJA, and now we will present two more. The first uses NICKEL-CADMIUM batteries, and the second a lead-acid car battery. Here is the circuit for the first option:

1. ZX Spectrum power supply; 2. battery holder and, of course, batteries (R14 or R20).

If you choose this option, buy the more expensive NICKEL-CADMIUM batteries, since they can be recharged and used for many years. With this solution, you can preserve the program in memory for a few minutes. That is a relatively short time, but at least you will not have to type the same program in again, even if it took several hours.

The second option uses a lead-acid car battery, which has a much greater capacity than the batteries mentioned above.

The program will remain in memory for several hours, or even days, depending on the battery. The battery does not have to be new for your needs, but it must be in good working order.

The circuit is the same as in the previous example, with one resistor added. The battery is trickle-charged through it with a current of a few milliamps. It will remain charged and ready for use if needed.

You can use any diode in place of the specified type, provided it can carry a current of at least 2 amperes.

1. Spectrum power supply; 2. battery (12 V).

Pay attention to the polarity: the diode must be connected the right way round.

Depending on which option you choose, you can install one of these simple circuits in a case together with the batteries or accumulator. You could also install the power supply in the same case.