DIY Pong - Part 2 of 4 -The Paddles

The Paddles

The two paddles (or bats) are identical. The paddle is dead simple. For each paddle, we need to define its horizontal position on the screen and how thick it is. These two values are fixed and will be set by two monostable multivibrators. Then we need to show its current vertical position controlled by the player's control pot. For this we again use a pair of monostable multivibrators, the second half being used to determine the size of the paddle which will be fixed.

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The first monstable U5A is triggered at the start of the horizontal scan. The duration of this monostable, determined by C5-R5 combination will fix the horizontal position of the paddle. For the Left Paddle, we set this to about 15μs into the scan line. For the Right Paddle, this is set by C10-R10, for about 50μs.

The second half of the CD4538 monostables U5B and U7B will set the thickness of the paddle. This is determined by C6-R6 and C8-R8. Both are set for about 1μs.

The second pair of monostables, U6A and U6B determines the play position and width of the Left Paddle. U6A is triggered from the start of the vertical scan. The player controls the variable resistor R9 in order to move the paddle up and down. The width of the paddle is set for about 2ms, determined by C8-R8.

This section is identical for the Right Paddle.

The only difference between the Left Paddle circuit and Right Paddle circuit is the value of R5 and R10, that is, the position of the paddle across the screen.

The AND result of the horizontal and vertical position information of each paddle defines the rectangular shape of the paddle on the screen.



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Here is a screen shot of the Right Paddle:
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DIY Pong - Part 1 of 4 - Getting Started
DIY Pong - Part 3 of 4 - The Ball
DIY Pong - Part 4 of 4 - The Play

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