Coin Toss Circuit

Posted on Feb 6, 2014

In this project you will build a coin toss circuit. It has three sections: a square-wave oscillator, a JK flip flop, and two LEDs (red & green). It uses CMOS digital ICs and MOSFET transistors. The schematic does not show the power and ground connections for the ICs. When powered from a 9V battery, both LEDs will light. When you press the switch, one LED shuts off and the other stays lit; but which one There`s

Coin Toss Circuit
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a 50-50 chance for either color. The square-wave oscillator uses one gate in the CD4093 IC. The IC contains four 2-input NAND gates as shown in figure 2. Digital signals are either high (+V) or low (0V). The output of a gate will switch between high and low depending on its inputs. The input-output behavior of a gate is defined by its truth-table. Table 1 is the truth-table for a 2-input NAND gate where A and B are the inputs and X is the output. A 0 represents low (0V) while a 1 represents high (+V). Mistakes happen, and unsoldering an IC is tedious. So in this project we will use IC sockets. Refer to figure 6 to see how the parts are arranged on the board, including jumper wires. Figure 7 shows how the parts and jumpers are soldered. Note that the leads of the switch need to be adjusted slightly to fit the holes in the board. Figure 7 shows the two strips of copper that run along the top and bottom of the board. They are used for +9V (red wire on battery clip) and ground (black wire). Drill a 1/8 inch hole between the two existing holes. Then feed the battery clip wires through and make a small knot. Then feed the black and red wires through the other two holes as shown. In figure 6 you can see the red and black wires inserted into holes and soldered on the copper side. Note the bare-wire jumpers, including the one between the two ICs which brings +9V to pins 5 & 6 of the CD4027. Since I cut the board down, it turned out...

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