2019-08-24 21:17:37, In: Electronics, DIY
The device, a TV Tennis game, has been made using designs from different sources, especially a description in "Radioamator" and images of the prototype. The general rule is similar to "Odyssey" but the signal mixing is simplified while still giving TV-friendly signals. There are only NPN signal transistors and 74 chips, to be exact one 7474 dual flipflop, 7473 as divider and 7493 as additional divider. Other chips are 7400, in many possible configurations. All other things like delays or integrations are made using discrete components. If someone wants to build a similar unit, prepare for a long tuning and selection of components.
This is a general view of the device. It has a power switch, 1/2 player switch and speed setting. Two controllers consist of X/Y pots, serve and "Lift" buttons which changes deflection direction.
The rear side has a composite/RF output, right and left controllers sockets and power connection.
This is the picture in "single" mode, in which one paddle is extended to a whole screen. The ball move is shown.
Inside, the power transformer is on the left. Then modules are present. In front, there are switches and a tuning board. In front, there also is a small high-ohm speaker. The transistor present on a backplane amplifies the digital signal from ball deflection and it is fed to speaker.
A detailed photo shows how the ball is extended in height - there is a 100uF capacitor connected in parallel when 1-player mode is selected. This capacitor increases delay to make the paddle higher. The holes below power transistor have been made later as I saw that there is a good 0.6-0.7A draw from the power unit. Let's review boards.
This is the power supply board. The uA723 chip is a typical linear power supply driver, which drives the power transistor on a heatsink. The Graetz bridge is on the right. The resistors in parallel are for current limiter set to ca. 0.9A.
The board A, frequencies generator, generates signals for a whole circuit. There are generally two signals coming from this module in different forms: Horizontal pulses are a high-frequency 15625Hz pulses. They are generated using a 1MHz oscillator (red part at the top-right), divided until 15625Hz is obtained. The vertical 50Hz signal is generated from power supply sine. The interferences are filtered out by 33pF capacitor (top, above 7400).
To maintain proper signal shape, the signals are filtered to spikes first, then these spikes are extended by RC circuits.
The signals come in different forms. First is a digital form of "spikes", digital form of extended pulses and a composite signal in proper proportions made with resistors.
Presence of this board will produce sync signals well enough to put most of "blue screens" out and show black screen.
The left paddle board consists of two parts: First is a delay circuit which sets a logic state when the voltage rising during delay is the same as voltage set by paddles. Two of these allow to control X/Y of paddle. These signals fire a monostable generators. Another part is related to paddle's shape, which consists of two RC extending circuits for getting width and height.
The right paddle module is exactly the same. The only differences are in paddle controllers. These two modules present in backplane allow to obtain paddles image on screen and throw them here and there. The "serve" buttons work by charging or discharging the capacitor, making paddle shift to the edge of screen and come back, quickly pushing the ball in front of it.
The ball generator module is in fact similar to paddles. The block is generated by delay circuits. Position of the block is changed by voltages on two module's pins. These voltages can be tuned by additional trimmers or ball moving board. Additional transistor circuits produce specific paddings to "lock" the ball in left or right side of the screen.
The most important part: Ball movement board. The board consists of rising/falling generators and a flipflop. The flipflop changes its state when the ball chenges direction. This allows to charge/recharge capacitors, making voltages for ball board. The ball speed can be regulated by resistors using to charge/discharge capacitors.
The tuning board consists of trimmers for setting various values. It sets the following things:
- Left and right curents for ball move "limits".
- Speed max/min values
- Main speed value
- Ball voltage "paddings".
In this photo we can see two additional circuits with transistors. One is an emitter follower to give composite-like output. The second transistor is for speaker signal. The missing board is for TV modulator, not present in current version.