Make-It-Yourself projects
Radio Electronics, june 1976

This project concerns an analog circuit which offers a strange PONG variant. The basic project has no sound and no on-screen scoring, and differs from PONG by the presence of a large square used as "bumper" in the middle of the screen (the ball bounces on it).

This article explains the basic version of the project. The july 1976 issue has the sound and digital on-screen scoring add-on circuits. As we don't have this issue, we couldn't include it here, but the most important part is there. However, it is interesting to see how the on-screen scoring part was done in this projet since it is digital, which is very rare for early projects like this one. Back in 1976, scoring was simply made using moving squares or lines. Here, it is done with real numbers. This requires the use of a character generator, which is mainly a ROM memory chip which contains the data to form the numbers. These memories are very small but contain sufficient space to store the numbers' data. Here is an example of how a number is stored in memory (we have replaced the 0's by dots for better reading):

    ...11111 -> #1F
    .......1 -> #01
    ...11111 -> #1F
    ...1.... -> #10
    ...11111 -> #1F

Therefore, 5 bytes are required for each number, hence a total of 50 bytes. It that case, a 64-bytes memory could be used (or two 32-bytes memories). Special character generators contain only the space needed by the data. Of course, this is only an example, but it shows how the bitmaps of the numbers were stored to be displayed. To finish, it is important to remember that these memory chips were not used like in modern computers. Instead of being driven by a processor (or other advanced component), they were drived by simple logic gates.

Click the photos to see them in large scale.

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