Red or green? Free Technical Library article. Scheme, description

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Red or green?. Radio - for beginners

Radio - for beginners

This can be conditionally called a slot machine, the scheme of which is shown in Fig. one.

Rice. 1 Slot machine "Red or green?"

It is formed by a rectangular pulse generator on logic elements DD1.1 and DD1.2, included by inverters, a JK flip-flop DD2 and transistors VT1 and VT2 with incandescent lamps HL1 and HL2 in collector circuits. The balloon of one of the incandescent lamps is colored red, the other green.

How does such a machine work and what is the task of the players? While the contacts of the SB1 button are not closed, the generator generates pulses, the repetition rate of which is determined mainly by the capacitance of the capacitor C1. The capacitance can be in the range of 1000 pF ... 1 uF. Pulses are fed to the input C of the JK-flip-flop DD2 and their downturns change its state to the opposite. The frequency of voltage level changes at the trigger outputs is half the frequency of the generator.

At intervals, when a high-level voltage appears at the direct output of the trigger (pin 8), the transistor VT1 opens and the HL1 lamp turns on. Transistor VT2 is closed at this time, since there is a low voltage level at its base. When the voltage is high at the inverse output (pin 6) of the trigger, this transistor opens and the HL2 lamp turns on. The transistor VT1 closes at this time and the lamp HL1 goes out. And so with each period of the generator pulses.

With the capacitor capacitance indicated on the diagram, the opening frequency of the transistors is at least 1 kHz. Therefore, the filaments of both lamps shine dimly. But it is worth pressing the button SB1 and thereby closing the capacitor C1, as the generation of pulses will stop. In this case, one of the incandescent lamps goes out, while the other, on the contrary, shines brighter. But which of them - red or green - will be turned on after pressing the button, it is impossible to say in advance, because it depends on the logical state of the trigger, in which it will be at the time of generation failure. One can only guess what, in fact, the players should do before pressing the generator start button.

The winner is the one who, with an equal number of button presses, say twenty, more times guesses the color of the lamp turned on after the generator stops.

Can the JK-trigger of such a slot machine be replaced by a counting D-trigger? Of course, you can, you just need to connect its input to the inverse output.

See other articles Section Beginner radio amateur.

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