Brookhaven's Instrumentation Division and Media & Communications Office invite the Lab community to celebrate the fiftieth anniversary of Tennis for Two

Many of the visitors enjoyed playing a recreated version of Tennis for Two, rebuilt by the Instrumentation Division's Peter Takacs, Gene Von Achen and Paul O'Connor, with Scott Coburn, Condensed Matter Physics & Materials Science Department.

Using Higinbotham's original plans, Takacs and his colleagues rebuilt the game with vintage parts, including mechanical relays and germanium transistors that first became commercially available in the 1950s. The original 1950s model analog computer that was made from vacuum tube circuits had to be simulated using modern integrated circuit chips.

guvcenter@bnl.gov

visitors@bnl.gov

//

The screen display was a side view of a tennis court. It looked like an upside-down " T, " with a shortened stem. This was the "net. " Each player held a prototypical paddle, a small box with a knob and button on it. The knob controlled the angle of the player's return, and the button chose the moment of the hit. A player could hit the ball at any time, providing it was on his side of the net. Gravity, windspeed, and bounce were all portrayed. For example, if you hit a ball into the net, it would bounce lower than a bounce off the "ground," and would eventually die.

The game was simple, but fun to play, and its charm was infectious. Potter remembers the popularity of the game: "The high schoolers liked it best. You couldn't pull them away from it." He's probably remembering young Dave Ahl, staring at the screen with a little voice inside him saying "this could be something important."

The ball and court lines were drawn and redrawn sequentially, at a rate that made for a flicker-free view of ground, net, and ball. This is an approach still used in game playfield display. However the method of ball manipulation was and remains unique.

Without becoming too bogged down in explanation, consider the following. An oscilloscope is capable of generating cartesian coordinate displays. That is to say, a dynamic "graph" can be drawn, plotting the deflection of x or y proportionally to the voltages input as x or y.
 
Higinbotham rigged up a circuit wherein the plot of these functions simulated the trajectory of a bouncing ball. Op-amps from a Donner Labs analog computer were used to generate this trajectory and to sense when the ball had struck the ground. When this occurred, a relay would be thrown, reversing the polarity of another op-amp, so that the ball would reflect its path and "take a bounce." Primitive, but effective.

Other op-amps and relays were used to determine whether or not the ball had hit the net. As mentioned earlier, rebound velocity from the net was lower than from the ground, providing an extra bit of realism.

Velocity, slowed continually by wind-speed, was simulated straightforwardly with a 10 meg. resistor.

A toggle switch allowed players to choose which side to serve from, and net height, as well as court length, were adjustable. There was no way a player could "miss" the ball, as a push of the paddle button would always result in a hit when the ball was on that player's side of the net. Unless the player chose the correct angle and timing for a return, however, the shot would not make it back to the opponent's side.

//

Higinbotham used four of the computer’s operational amplifiers to generate the ball’s motion while the computer’s remaining six amplifiers sensed when the ball hit the ground or net and switched controls to the person in whose court the ball was located. In order to generate the court, net, and ball on screen, it was necessary to time-share these functions.

“The real innovation in this game is the use of those ‘new-fangled’ germanium transistors that were just becoming commercially available in the late 1950s,” said Peter Takacs of Brookhaven Lab’s Instrumentation Division, who is currently working to rebuild a playable Tennis for Two. “Higinbotham used the transistors to build a fast-switching circuit that would take the three outputs from the computer and display them alternately on the oscilloscope screen at a ‘blazing’ fast speed of 36 Hertz. At that display rate, the eye sees the ball, the net, and the court as one image, rather than as three separate images.”

In 1958, when Tennis for Two was first introduced, the oscilloscope display was only five inches in diameter. In 1959, the game was improved. A larger screen between 10 and 17 inches in diameter was used and players could select variations of tennis on the moon, with low gravity, or on Jupiter, with high gravity.

//

#EOF