These gates are called Resistor-Transistor Logic (RTL) because they depend on using transistors as switches with pull-up or pull-down resistors to make the logic functions work properly. In the first part of the lab you will build a circuit to implement your solution to this logic problem using the transistor-based logic gates you learned about in the last lab. Before you come to lab you will be asked to plan out the solution to a logic problem. In this lab we will look at combining the simple logic gates we used in the last lab to build more complicated logic circuits that can evaluate a set of input conditions and decide what action to take. So far, the timer has become a countdown timer.ECE U401/U211-Introduction to Electrical Engineering Lab
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The connection circuit diagram of the above-mentioned Y4, Y3, Y1 conversion specific physical objects is shown in Figure 7.įigure 7. Y 4, Y 3, Y 1 Conversion Specific Physical Connection Diagramįigure 8 shows the actual picture of the countdown timer. Knowing that the XOR gate operation can be completed, the Y3 conversion can be completed. In summary, we can follow the logical relationship as follows: The latter are two four-input NAND gates, which are used to obtain Y4 from the non-reAND of Q4, Q3, and Q2.
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The former are four two-input NAND gates, which are used to complete the conversion of Y1 and generate the negation of Q4, Q3, and Q2. Two kinds of chips 74LS00 and 74LS20 are uesd here. Countdown Circuit Diagram 5.2 Implementation of Scheme Design Timer Circuit Displaying 2 Digitsįigure 5. After adding the above conversion circuit, it becomes the figure 3 shows the countdown circuit.įigure 4. The figure? shows a two-digit timer circuit. Therefore, as long as you choose a circuit that can complete the above logic conversion relationship, you can realize the design from a timer to a countdown timer.
#Nand gate ic 7400 datasheet code#
Corresponding BCD Code Displayed by (Down)Timer
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The result displayed by each digit of the timer is an incremental value, such as 0.1.2.3.4.5.6.7.8.9. Generally, there are two design ideas for turning a timer into a countdown timer: First, change the counting chip in the timer Second, reset the function of the chip.īesides, there is actually another way to achieve this goal: By appliying the 74LS00 and 74LS20 chips to "reverse" the results on the display, so as to achieve the purpose of counting down.
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At this time, the LEDs are individually lit from D16.D1.įrom the above we can see that: the LED lights turn on from D1 to D16, and then back to D1 from D16, and so on.
#Nand gate ic 7400 datasheet generator#
The signal generator mainly uses two TTL integrated circuits (74LS00 and 74LS221). The circuit diagram is shown in Figure 2 and it’s a simple pulse signal generator circuit. NAND gates 1, 2 and external RC time constant components form an oscillator circuitĪs long as the capacity of C is changed, square wave outputs of different frequencies can be obtained.Let’s take a look at the figure below. It’s a square wave generator circuit. This circuit contains a 74LS00 Nand Gate integrated circuit.įigure 1. Square Wave Generator Circuit Diagram This Video is An Introduction of 7400 Logic Devices