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Cheap dirty trick that gave color graphics to the first home computers

Video game pioneer Alan Elkorn talks about how he showed Steve Wozniak a hack that allowed the Apple II computer to work with colors, and where did the famous “blip” sound come from in Pong



Atari Pong home console, which went on sale to The Sears under the Tele-Games brand in 1975.

We recently published an article on a modern amateur computer using a very old hack: NTSC artifact colors. This hack allowed digital systems that did not have separate graphics cards to issue color images, exploiting the features of decoding a television signal.

The most famous example of using NTSC artifact colors is the 1977 Apple II computer. The use of this hack by Steve Wozniak in this computer attracted wide attention to him. It was later used on IBM PC and TRS-80 Color computers. However, few people knew where this idea came from, so we were very excited when a comment on this topicto that article was left the legend of electronics and video games, Alan Elkorn. It turns out that the ancestor of the first color computer graphics can be considered a cheap test device, which was used in California tele-repair shops in the 1960s. IEEE Spectrum magazine chatted with Elcorn to learn more.


Alan Elkorn with Pong

IEEE : NTSC analogue TVs generate color by tracking the phase of the signal relative to the reference frequency. How did you get this test device in your hands, and how did it work?

Alan Elkorn : When I was 13-14 years old, my neighbor, who lived across the street, kept a repair shop for TVs. I ran to him; and just then my father sent me to RCA radio and TV repair courses. Therefore, by the time I got to Berkeley, I was already working as an itinerant TV repairman, and thus even paid for college. And in one workshop there was a very cheap and dirty color rectangle generator designed to test TVs. Instead of correctly delivering color by synthesizing phases and all that jazz, he simply used a 3.58 MHz crystal (carrier frequency of the color signal), minus 15.750 kHz, horizontal frequency. Therefore, each phase he lagged behind 360 degrees. If you display this signal on the screen, you get a color bar, from the left edge to the right. It was really the cheapest and dirtiest way to achieve this!

IEEE : How did you come up with the idea of ​​using NTSC “not according to instructions”?

AE: I met a cheap dirty way while working as a repairman. And then I got a job at Ampex (at that time - a leader in audio and video technology). In Ampex, I first saw how a picture on a video is obtained using digital technology; they then reached an acceptable speed, and it opened my eyes. And then I switched to Atari. Nolan Bushnell, co-founder of Atari, decided to enter the home consumer electronics market. In 1972, we released the monochrome arcade game Pong, which gave us the opportunity to develop from scratch, but he always wanted to work in the home consumer electronics market. Together with another engineer, we squeezed all the logic of the Pong game to a single N-channel silicon chip. And at some point during the development, Nolan said: "And by the way, the game still has to be color." However, I knewthat he will check such a number, so he has already chosen a crystal at a frequency of 3.58 MHz minus 15.750 kHz.

IEEE : Why did you suspect that he would throw something like that?

AE: Because we had no plan. There were no drafts, no business plan. Everything was in Nolan’s head. I think you are aware that in general, from the beginning, the Pong arcade was started as a test for me, so that I could practice developing the simplest game possible. However, Nolan lied to me, and said that it would be a product for home consumers. As a result, it was rather sad, I could not do it - I stuffed about 70 integrated circuits there, and the device turned out to be expensive for a home game. And then Nolan suddenly decided that it would be suitable for a slot machine! And when we were already finished making Pong for the machine, Nolan said: “Well, where is the sound somewhere?” I ask him: “I mean, sound?” I did not want to add more components there. He said: "I want to hear the roar of the crowd, the applause of thousands of people." Ted Dubney,another company owner said: “I want to hear the sounds of 'buuu' and the whistle.” And I replied to them: “Well then, I’ll be back soon.” I climbed there with the probe, looking for a vertical synchronization scheme with a frequency that would fall into the auditory range. I found such a place, I used the 555 timer (to connect the circuit to the speaker for a short time and give out peeping sounds). I said: “It will be like this, Nolan; and if you don’t like it, then do it yourself. ” And he said, “OK.” And after that I readI said: “It will be like this, Nolan; and if you don’t like it, then do it yourself. ” And he said, “OK.” And after that I readI said: “It will be like this, Nolan; and if you don’t like it, then do it yourself. ” And he said, “OK.” And after that I readarticles where praises were sung to this sound! And the whole idea was to get the most out of the minimum set of components. And it worked. We had $ 500 left in the bank. We had nothing, and we just put our game on the market. Time was running out.

IEEE : And in the home version of Pong, did the graphics just change color from one to the other side of the screen?

AE: Yes, the goal was only to write on the box: “Color!” And this joke happens: the home version of Pong becomes a hit. In the years 1974-75. A big hit. An advertisement is being made for television. Advertisers are trying to record a Pong signal on a videotape. And they called me from some studio and said: “Why can't we make her output the image to a VCR?” I say: “Well this is not really a video! There is no interlacing ... Consider it a PAL. Run it through a regular converter. ”

IEEE : How did Wozniak find out?

AE: At that time in Silicon Valley we had no secrets. I hired Steve Jobs out of luck. He was not even an engineer. And his friend Voz worked at HP, but with us it was much more fun to hang out. We had production, we collected 30-50 slot machines, and they stood in the workshop. Jobs didn’t get along with other employees, so he came to work at night. Woz, it happened, came to play during the hours when Jobs worked, and sometimes Jobs persuaded Woz to do the work for him. And I liked Woz. I want to say, he is just a genius, he was right. Just awesome.

When they made Apple II, I helped them. I lent them my oscilloscope. I had 465 Tektronix, and I still have it. And they developed Apple II with it. I used to do Pong with it. I did something for them, in my opinion, in connection with the storage of data on audio tapes. And then I remember how Woz showed a trick with high resolution color. We sat, I explained the principle to him, and said: “Well, that's how NTSC should work in principle.” And then he said: “Well, actually, if you do everything at such a frequency, and with the help of rectangular pulses ...” And he explained the whole trick. And he took it into service. That was the tradition. It was normal, I kind of boasted to him!

IEEE: When today people are motivated to tinker with electronics, to experiment with it, usually there are such things as Arduino, concentrated on the digital. Don't you think analog electronics are bypassed?

AE : Definitely. There was such a period, it seems to me, somewhere in the 90s, when it came to the point of absurdity, and it was simply impossible to find a good analog engineer. And for certain things, analog engineers are needed. Good analog engineers were paid pretty well at that time. They earned a lot of money because they were few. But most of the kids just want to get rich. And this leads to the path associated with programming something for the iPhone. And that’s it. He got rich and went. However, analog electronics is a very important and valuable area.

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